WO2025213233A1

WO2025213233A1 - Electroactive materials

Info

Publication number: WO2025213233A1
Application number: PCT/AU2025/050356
Authority: WO
Inventors: Udo Bach; Muhammad Kalim Kashif
Original assignee: Monash University
Current assignee: Monash University
Priority date: 2024-04-12
Filing date: 2025-04-11
Publication date: 2025-10-16
Anticipated expiration: 2026-10-12

Abstract

The present invention provides an electrically conducting metal phenolic network (MPN) comprising (i) metal cations coordinated by deprotonated polyphenol, wherein the metal cations are cations of the same metal element in different oxidation states, or are cations of different metal elements, and (ii) a counter-ion.

Description

ELECTROACTIVE MATERIALS

FIELD OF THE INVENTION

The application relates generally to electroactive materials, and in particular to coordination materials and methods of making them.

BACKGROUND OF THE INVENTION

Electrically conductive materials are omnipresent in our everyday life. Typical examples include metals such as silver, copper, and aluminium, carbon allotropes such as graphite, graphene and carbon nanotubes and conductive polymers such as poly aniline or poly (3,4- ethylenedioxy thiophene). These materials differ greatly from each other in their physical properties and specific electrical conductivity.

Applications for these materials and coatings are manifold and include electromagnetic shielding, electronics (printed circuit boards), electrocatalysis, fuel cells and electrical storage devices (capacitors, supercapacitors, batteries) and bioelectronics. Each of these applications relies on the intrinsic electrical conductivity of these materials, with vastly different requirements towards their general physical properties.

A convenient way to produce conductive films and coatings is via solution-processing methods such as printing and painting. Wet-chemical deposition has previously been demonstrated for films which owe their electrical conductivity from the presence of either metal particles, carbon allotropes, conducting polymers or a mixture of those. Examples include silver paints, graphite-based paints and conductive polymer-based paints. Each of these films have their specific strengths and weaknesses.

Silver-based paints are highly conductive but comparatively expensive due to the material cost of silver. Silver particles also typically don’t form strong adhesive bonds between each other or other surfaces. This necessitates the addition of binders (typically polymers) to form adhesive films. Silver can be replaced with lower cost materials such as nickel, albeit with a significantly lower corrosion resistance.

The fabrication of conductive coatings based on graphite, graphene or carbon nanotubes has also been widely reported. Graphite is widely abundant. Graphite however is a material with a 2D structure and low adhesion between its structural graphite plains. This makes graphite an excellent material for lubrication but also causes issues with the mechanical strength of graphite-based films or the adhesion of these materials onto other surfaces.

Some carbon allotropes such carbon nanotubes are also of concern due to their potential risk to the human health. Conducting polymers such as poly (3, 4-ethylenedioxy thiophene) (PEDOT) can be used to produce electrically conductive films which at the same time can show some optical transparency. These materials are however relatively expensive to produce, suffer from weak adhesion to substrates such as ITO-coated glass, while also showing reduced electrochemical stability over time.

Conductive films used in charge storage devices such as supercapacitors or batteries often require a high internal surface area and porous structure. Carbon based films are often used here. The range of applications and operation conditions is extremely diverse, defining a need for an equally diverse selection of materials to choose from. Electrocatalysis typically is a heterogeneous process which requires materials that can conduct electricity directly to the catalytically active sites. High porosity is again beneficial as the rate of the heterogenous catalytic reaction typically scales with the internal surface area of the electrode.

This clearly defines a need for materials that are easy to chemically tune and combine intrinsic electrical conductivity with catalytic activity and a high internal surface area.

SUMMARY OF THE INVENTION

From a structural standpoint, the MPN of the invention (also referred to herein interchangeably as "EMPN") is a coordination compound in which the cations are coordinated to the polyphenol as a result of a donor-acceptor mechanism or Lewis acid-base interaction between the cations (acting as the acceptors) and ionic or radical centres in the polyphenol (acting as the donors). By their own nature, polyphenols can act as multi-dentate chelating ligands. By “chelating ligand” is meant a ligand that coordinates a cation simultaneously at two or more locations. Depending upon the number of coordination sites, the polyphenol can offer bidentate, tridentate and tetradentate coordination sites, which in turn can alter the redox potential of the ligated cation.

Structurally, and without wishing to be limited by theory, the MPN is believed to present as a polyphenol framework having intercalated counter-ion(s).

The MPNs described herein comprise at least one polyphenolic compound (also referred herein as "PPC") and cations of at least one metal element, which together have the ability to form an MPN. If cations of only one metal element are present, they have said element present in different oxidation states. Due to the presence of redox active species during the synthesis and post-synthesis processes the redox states of the metal cations in the final product can be different to the redox states of the starting materials from which it is formed.

MPNs as described in this invention can also comprise cations from different metallic elements and/or more than one type of PPC. Additional components may be present in the MPN other than the metal cations and PPCs, however those may be side products formed during the chemical synthesis or post-processing steps, for example steps of the kind described herein.

A wide range of metals can be used to form the MPN of the invention. This offers a range of opportunities to fine-tune the electrochemical and structural properties of the MPN, which can be synthesised with characteristics tailored to the intended application.

Advantageously, co-existence of different oxidation states of the same metal or the presence of cations of different metallic elements can induce or enhance the electrical conductivity of the material. Accordingly, the MPN is electrically conductive. As used herein, the expression "electrically conductive" means conductivity higher than, for example least lOx, that of pure tannic acid (4.37xl0^-11 S-cm^-1). Accordingly, in some embodiments the MPN has an electric conductivity larger than 4.37xl0^-11 S-cm^-1.

Polyphenols are aromatic compounds which carry more than one phenolic group. Polyphenolic compounds (also referred herein as "PPCs") may be any polyphenol that can coordinate at least two cations having different oxidation state or alternatively metal cations of 2 different elements. Accordingly, as used herein the term "polyphenol" refers to a phenol having at least two hydroxy groups in the same molecule, also known as a "multivalent phenol". Depending on the number of the hydroxy groups, the polyphenol may be referred to as dihydric polyphenol, trihydric polyphenol, tetrahydric polyphenol, etc.

Examples of suitable PPCs which can form the MPNs of the invention include flavonoids, phenolic acids, stilbenes, coumarins, and a combination thereof. In some embodiments, the polyphenol is a flavonoid for which basic structure is a carbon skeleton built of 2 phenyl rings (Ce) bridged by a chain of 3 carbon atoms (C3) forming a heterocyclic 6-membered ring with oxygen and 2 carbon atoms from an adjacent phenyl ring: C6-C3-C6. Suitable examples of such flavonoids include flavonols, flavones, flavanones, flavan-3-ols, anthocyanidins, isoflavones, and a combination thereof.

In some embodiments, the polyphenol has a phenolic acid structure selected from hydroxybenzoic acid (Ce-Ci), cinnamic acid (C6-C3), and a combination thereof. Suitable examples of hydroxylbenzoic acids include, tannins, gallic acid, tannic acid, albumin tannate, epigallocatechin, salicylic acid, vanillic acid, dopamin and a combination thereof. Suitable examples of cinnamic acid include caffeic acid, ferulic acid, and a combination thereof. In some embodiments, the polyphenol is a phenolic acid which is selected from gallic acid, tannic acid, and a combination thereof.

In some embodiments, the polyphenol is selected from stilbenes (C6-C2-C6 structure, such as resveratrol), lignans (C6-C3-C3-C6), coumarins (C6-C3), and a combination thereof.

The polyphenol may be any naturally occurring or chemically synthesised polyphenol. Due to the abundance of polyphenols in nature, the MPN of the invention can be derived from readily available natural, renewable resources. This ensures that the MPNs of the invention are environmentally benign and can be produced at low cost using cheap and abundant raw materials. It can be envisaged that one or several of the PPC starting materials are naturally occurring PPCs which have been chemically modified.

In some embodiments, the polyphenol is selected from a synthetic or plant polyphenolic material, tannins, tannic acid, gallic acid, a catechin, a flavonoid, a chaicone, a procyanidin, and an anthocyanidin.

In some embodiments, the EMPN presents as a solid. By EMPN presenting “as a solid” it is meant that the EMPN as a whole is characterised under a given set of ambient conditions (e.g. room temperature) by sufficient structural rigidity to support its own weight and maintain its shape in the absence of external factors such as constrictions (e.g. a container) or applied forces. For instance, EMPNs that present as a solid in the context of the invention may comprise a liquid solvent content of 10% or less by volume.

In some embodiments, the EMPN is in the form of a film, gel, or powder.

The MPNs of the invention are intrinsically electrically conductive. The MPNs of the present invention possess intrinsic electrical conductivity which can be at least 10 times higher than conductivity reported for tannic acid itself (4.37xl0^-11 S-cm^-1). In one specific embodiment, the MPN films can reach conductivities of up to 28 S-cm ¹. Given the intrinsic electric conductivity of the MPNs of the invention, the terms "MPN" and "EMPN" are herein used interchangeably. Accordingly, "EMPNs" (electrically conducting metal polyphenolic networks) in the context of the present invention are considered "electrically conductive" metal phenolic networks if their specific electrical conductivity is at least 10 times higher than the conductivity of a pure tannic acid film.

There is also provided a composite comprising an electrically conducting metal phenolic network (EMPN) as described herein, wherein the EMPN is mixed or layered with a topcoat. Said topcoat may comprise polyacrylic or polyurethane.

There is further provided a method of making an electrically conducting metal phenolic network (EMPN) of the kind described herein, the method comprising the steps of: a) combining at least one metal cation source and the polyphenol in a solution, wherein the polyphenol is deprotonated to obtain a cation/polyphenol coordination compound, the cation/polyphenol coordination compound comprising the one or more metal cations, and b) combining the cation/polyphenol compound with a counter-ion salt in a solution to obtain the EMPN.

The EMPNs of the invention can be implemented in a wide range of applications. The following list provides examples of salient applications that have been demonstrated with examples as well those that could be envisaged on the basis of the knowledge about invention:

• Applications with provided examples include electrically conductive materials that can be applied as a coating on top of a substrate of choice, to form strongly adhesive, electrically conductive films. In particular materials where such films can be produced via solution-processing or painting techniques or via a spray or powder coating process,

• Electrically conductive materials that can be produced as self-standing films,

• Electrically conductive materials that could be used to mitigate electromagnetic radiations,

• Electrically conductive materials with a large internal surface area, i.e. for the fabrication of supercapacitors,

• Electrically conductive materials that allow for the transmission of light,

• Electrically conductive materials which are environmentally benign and not harmful to the human health,

• Electrically conductive materials which can be synthesises at least partially from abundant low-cost renewable resources,

• Following applications are envisaged,

• Electrically conductive materials with catalytic properties, including photocatalytic and electrocatalytic properties, and

• Electrically conductive materials that are stable towards corrosion or other decomposition pathways and maintain their conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be now described with reference to the following nonlimiting drawings, in which:

Figure 1 shows attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectrum of pure tannic acid (solid line) and an electrically conducting EMPN (dashed line) obtained in accordance with Example 4,

Figure 2 shows voltage and current read-out of a 4-point probe (1 mm probe spacing) conductivity meter in contact with an EMPN film, obtained in accordance with Example 5,

Figure 3 shows performance of EMPNs as charge storage device. 3a) Cyclovoltammogram of an EMPN compared to carbon black. Black curve: Cyclovoltammogram of a 25 micron thick solid EMPN film deposited onto indium-doped tin oxide coated glass comprising Nickel based EMPN. Starred black curve: Cyclovoltammogram of a 25 micron thick film of carbon black, measured on a film obtained in accordance with Example 6. In Fig 6a, 2.0 mg mass of electroactive active material is used. The electrolyte contained 100 mM LiOH dissolved in a 1: 1 mixture of acetonitrile and valeronitrile. Scan rate: 10 mV/s,

Figure 4 shows data of a chemiresistive ammonia sensor using EMPN as the active sensing layer in accordance with Example 7,

Figure 5 shows the optical absorbance spectrum of a 0.5 micron thick EMPN film, obtained in accordance with Example 8,

Figure 6 shows optical transmittances at a wavelength of 550 nm as a function of sheetresistance for EMPN films obtained in accordance with Example 9, and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) films of various thicknesses. The comparative data points for PEDOT:PSS have been replotted from data published by Seongho Jo et al., Materials Today: Proceedings 10 (2019) 448-455,

Figure 7 a) and 7b) show differential pore volume as a function of pore width for an EMPN powder sample obtained in accordance with Example 10. This data is derived from the analysis of Brunauer-Emmett-Teller (BET) nitrogen (a) and carbon dioxide (b) adsorption isotherms. The analysis yielded a BET surface area of 104.7 m²/g and 161.5 m²/g for nitrogen and carbon dioxide, respectively,

Figure 8 shows powder x-ray diffraction (XRD) data of two different EMPN films obtained in accordance with the procedure of Example 11,

Figure 9 shows high resolution scanning electron micrograph of an iron based EMPN film deposited on fluorine doped tin-oxide glass slide at high temperature (100-110°C) using DMSO as solvent, obtained in accordance with the procedure of Example 12,

Figure 10 shows Raman spectra of an EMPN and an EMPN film drop casted on glass obtained in accordance with the procedure of Example 13, using wavelength of excitation light source of 510 nm, Figure 11 shows thermoelectric voltage response of EMPN film obtained in accordance with the procedure of Example 14,

Figure 12a shows electromagnetic transmission spectra depicted by S21 parameters of the absorber films (iron and vanadium based EMPN mixed with 5 wt % carbon obtained with Network Analyzer connected with an APC-7 connector. Figure 12(b-c) show the electromagnetic interference shielding depicted by a freestanding EMPN based composite film in accordance with the procedure of Example 15,

Figures 13 a)-c) show XPS spectra of an Fe-EMPN film obtained in accordance with the procedure of Example 16,

Figures 14 a)-c) show XPS spectra of a Ti-EMPN film obtained in accordance with the procedure of Example 17,

Figure 15 shows capacitive touch sensor device obtained in accordance with the procedure of Example 18, and

Figure 16 shows current density (/^-potential (V) characteristics of the best-performing dye- sensitized solar cell (DSC) fabricated using Fe based EMPN as hole transport material, obtained in accordance with the procedure of Example 19.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an electrically conducting metal phenolic network (EMPN).

The EMPN of the invention is a coordination compound in which the cations are coordinated to the polyphenol as a result of a donor- acceptor mechanism or Lewis acid-base interaction between the cations (acting as the acceptors) and ionic or radical centres in the polyphenol (acting as the donors). These EMPNs are coordination compounds containing polyphenolic compounds (PPCs) and metal cations, in particular transition metal cations.

By their own nature, polyphenols can act as multi-dentate chelating ligands. By “chelating ligand” is meant a ligand that coordinates a cation simultaneously at two or more locations. Depending upon the number of coordination sites, the polyphenol can offer bidentate, tridentate and tetradentate coordination sites, which in turn can alter the redox potential of the ligated cation. The structure of metal-phenolic networks may be highly variable. The fraction of the phenolic groups which has established chelate-type bonds to metal cations is variable and might vary from molecule to molecule within the EMPN. Phenol groups which did not establish chelate bonds to a neighbouring metal centre remain either in their phenolic state or could be de-protonated depending on previous processing steps.

The coordination number for every metal cation can also be variable. Also, the ratio of intra- to intermolecular crosslinking can vary. Depending on the nature and oxidation state of the metal cation(s) and the average number of established chelate-type bonds the metal-phenolic networks will also contain additional ionic compounds to maintain charge neutrality. This may be better understood with reference to an example. An arrangement of one Fe²⁺ cation which established 2 chelate type bonds with 2 neighbouring polyphenols will carry two negative charges. These charges need to be compensated by the presence of two excess cationic charges inside the metal-phenolic network. An arrangement of one V⁵⁺ cation which established 2 chelate type bonds with 2 neighbouring polyphenols will carry 1 positive charge. This needs to be compensated by the presence of one excess anionic charge inside the metal-phenolic network.

Without wanting to be limited by theory, it is believed that in presence of transition metal cations PPCs can act as either antioxidants or prooxidants. This means that they can potentially be partially oxidised or reduced during the EMPN synthesis or any of the postsynthesis processes. This partial oxidation or reduction might either occur accidentally as a result of the preparation conditions or could be induced deliberately.

Due to the redox activity of the polyphenol, or any of the other compounds present during the synthesis of the metal-phenolic network or any of the post-processing steps, the oxidation state(s) of the metals used as precursors to form the metal-phenolic network can differ from the oxidation stage(s) of the metal cations present in the resulting metal-phenolic network.

In the EMPN of the invention, the metal cations are cations of the same metal element in different oxidation states or are cations of different metal elements.

In some embodiments, the metal cations are cations of the same metal element in different oxidation states.

In some embodiments, the metal cations are cations of different metal elements. In those instances, the metal cations may or may not have same oxidation state.

There is no actual limitation on the number of different metal elements present in the EMPN, provided the EMPN is an EMPN of the kind described herein. For instance, the EMPN may comprise metal cations which are actions of at least 2 metal elements. In some embodiments, the EMPN comprises metal cations that are cations of at least 3 metals elements, at least 4 metal elements, and so on.

The metal element(s) may be any metal element(s) that can be coordinated in cation form by a polyphenol. The metal element(s) may be selected from one or more alkali earth metals, transition metals, and lanthanide metals. In some embodiments, the metal element(s) is selected from one or more of magnesium, calcium, cadmium, strontium, barium, iron, aluminium, ruthenium, rhodium, terbium, vanadium, chromium, manganese, zinc, copper, cobalt, nickel, molybdenum, titanium, zirconium, cerium, europium, and gadolinium.

In some embodiments, the metal cations are selected from one or more of Fe⁶⁺, Fe⁴⁺, Fe³⁺, Fe²⁺, Fe⁺, Fe, Cu⁴⁺, Cu³⁺, Cu²⁺, Cu⁺, Cu, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Sc³⁺, Sc²⁺, Sc⁺, Y³⁺, Y²⁺, Y⁺, Ti⁴⁺, Ti³⁺, Ti²⁺, Zr⁴⁺, Zr³⁺, Zr²⁺, Hf⁴⁺, Hf³⁺, V⁵⁺, V⁴⁺, V³⁺, V²⁺, Nb⁵⁺, Nb⁴⁺, Nb³⁺, Nb²⁺, Ta⁵⁺, Ta⁴⁺, Ta³⁺, Ta²⁺, Cr⁶⁺, C ⁺, Cr⁴⁺, Cr³⁺, Cr²⁺, Cr⁺, Cr, Mo⁶⁺, MO⁵⁺, MO⁴⁺, MO³⁺, MO²⁺, MO⁺, MO, W⁶⁺, W⁵⁺, W⁴⁺, W³⁺, W²⁺, W⁺, Mn⁷⁺, Mn⁶⁺, Mn⁵⁺, Mn⁴⁺, Mn³⁺, Mn²⁺, Mn⁺, Re⁷⁺, Re⁶⁺, Re⁵⁺, Re⁴⁺, Re³⁺, Re²⁺, Re⁺, Re, Ru⁸⁺, Ru⁷⁺, Ru⁶⁺, Ru⁴⁺, Ru³⁺, RU²⁺, OS⁸⁺, OS⁷⁺, OS⁶⁺, OS⁵⁺, OS⁴⁺, OS³⁺, OS²⁺, OS⁺, OS, CO⁵⁺, CO⁴⁺, CO³⁺, CO²⁺, CO⁺, Rh⁶⁺, Rh⁵⁺, Rh⁴⁺, Rh³⁺, Rh²⁺, Rh⁺, Ir⁶⁺, Ir⁵⁺, Ir⁴⁺, Ir³⁺, Ir²⁺, Ir⁺, Ir, Ni³⁺, Ni²⁺, Ni⁺, Ni, Pd⁶⁺, Pd⁴⁺, Pd²⁺, Pd⁺, Pd, Pt⁶⁺, Pt⁵⁺, Pt⁴⁺, Pt³⁺, Pt²⁺, Pt⁺, Ag³⁺, Ag²⁺, Ag⁺, AU⁵⁺, AU⁴⁺, AU³⁺, AU²⁺, AU⁺, Zn²⁺, Zn⁺, Zn, Cd²⁺, Cd⁺, Hg⁴⁺, Hg²⁺, Hg⁺, B³⁺, B²⁺, B⁺, Al³⁺, Al²⁺, Al⁺, Ga³⁺, Ga²⁺, Ga⁺, In³⁺, In²⁺, In¹⁺, Tl³⁺, Tl⁺, Si⁴⁺, Si³⁺, Si²⁺, Si⁺, Ge⁴⁺, Ge³⁺, Ge²⁺, Ge⁺, Ge, Sn⁴⁺, Sn²⁺, Pb⁴⁺, Pb²⁺, AS⁵⁺, AS³⁺, AS²⁺, AS⁺, Sb⁵⁺, Sb³⁺, Bi⁵⁺, Bi³⁺, Te⁶⁺, Te⁵⁺, Te⁴⁺, Te²⁺, La³⁺, La²⁺, Ce⁴⁺, Ce³⁺, Ce²⁺, Pr⁴⁺, Pr³⁺, Pr²⁺, Nd³⁺, Nd²⁺, Sm³⁺, Sm²⁺, Eu³⁺, Eu²⁺, Gd³⁺, Gd²⁺, Gd⁺, Tb⁴⁺, Tb³⁺, Tb²⁺, Tb⁺, Db³⁺, Db²⁺, Ho³⁺, Er³⁺, Tm⁴⁺, Tm³⁺, Tm²⁺, Yb³⁺, Yb²⁺, and Lu³⁺.

In some embodiments, the metal cations are selected from one or more of Fe²⁺, Fe³⁺, Cu¹⁺, Cu²⁺, Co²⁺, Ni²⁺, RU²⁺, Zr²⁺, Mn²⁺, Eu³⁺, V³⁺, Zn²⁺, B³⁺, Be²⁺, Mg²⁺, Ca²⁺, Ba²⁺, Al²⁺, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Sc²⁺, Y²⁺, Ti²⁺, Zr²⁺, V²⁺, Nb²⁺, Ta²⁺, Cr²⁺, Mo²⁺, W²⁺, Mn²⁺, Re²⁺, Li¹⁺, Cs¹⁺,Os²⁺, Co²⁺, Rh²⁺, Ir²⁺, Ni²⁺, Pd²⁺, Pt²⁺, Cu²⁺, Ag²⁺, Au²⁺, Zn²⁺, Cd²⁺, B²⁺, Al²⁺, Ga²⁺, Si²⁺, Sn²⁺, Pb²⁺, Hg²⁺, As²⁺, Te²⁺, La²⁺, Ce²⁺, Pr²⁺, Sm²⁺, Gd²⁺, Nd²⁺, Db²⁺, Tb²⁺, Tm²⁺, and Yb²⁺.

The polyphenol may be any polyphenol that can coordinate at least two cations having different oxidation state. Accordingly, as used herein the term "polyphenol" refers to a phenol having at least two hydroxy groups in the same molecule, also known as a "multivalent phenol". Depending on the number of the hydroxy groups, the polyphenol may be referred to as dihydric polyphenol, trihydric polyphenol, tetrahydric polyphenol, etc.

Examples of suitable polyphenols making the EMPN of the invention include flavonoids, phenolic acids, stilbenes, coumarins, and a combination thereof.

In some embodiments, the polyphenol is a flavonoid which basic structure is a carbon skeleton built of 2 phenyl rings (Ce) bridged by a chain of 3 carbon atoms (C3) forming a heterocyclic 6-membered ring with oxygen and 2 carbon atoms from an adjacent phenyl ring: C6-C3-C6. Suitable examples of such flavonoids include flavonols, flavones, flavanones, flavan-3-ols, anthocyanidins, isoflavones, and a combination thereof. In some embodiments, the polyphenol has a phenolic acid structure selected from hydroxybenzoic acid (Ce-Ci), cinnamic acid (C6-C3), and a combination thereof. Suitable examples of hydroxylbenzoic acids include, tannins, gallic acid, tannic acid, albumin tannate, epigallocatechin, salicylic acid, vanillic acid, and a combination thereof. Suitable examples of cinnamic acid include caffeic acid, ferulic acid, and a combination thereof.

In some embodiments, the phenolic acid is selected from gallic acid, tannic acid, and a combination thereof. In some embodiments, the polyphenol is tannic acid.

When the first metal cation and the second metal cation are cations of the same metal elements, the EMPN of the invention has a structure that can be represented by the following formula (I): n P(OH)_m + a M l¹'- + b M2^r+ + (nx-aq-br)

P(OH)_m polyphenol with m hydroxy groups

Ml^q+ First coordinating metal cation q charge of first cation Ml

M2^r+ Second coordinating metal cation (Ml and M2 can be the same element or different elements)

R charge of second cation M2

C^z+ Non-coordinating cation (metallic or non-metallic) with charge ‘z’ x average number of phenol groups of every polyphenol which formed a chelate bond to a coordinating metal and accordingly were deprotonated nx-aq-br number of balancing positive charges required: negative charges from the partially deprotonated phenol minus positive charges of the coordinating metal cations Ml and M2 (when this number is negative, balancing anions are needed). The EMPN of the invention comprises a counter-ion. Without wishing to be limited by theory, it is believed the counter-ion plays a dual role. On the one hand, presence of the counter-ion ensures the EMPN is, macroscopically, electrically neutral such that the first and second metal cations can coexist in coordination with the polyphenol having different oxidation states. On the other hand, the counter-ion ensures mobility of the charges embedded within the EMPN, which derive from charge imbalance linked to the different oxidation states of the cations.

Different from the metal cations coordinated by deprotonated polyphenol, the counter-ion is not involved in the coordination structure of the EMPN. Without wishing to be limited by theory, from the structural standpoint the counter-ion is believed to exist within the EMPN as an intercalated ionic species within the structural matrix formed by the cations/polyphenol framework to ensure the overall neutrality of the framework.

Accordingly, the counter-ion may be any ionic compound that can exist as intercalate filling species within the structural matrix formed by the cations/polyphenol framework. The following examples are included to help clarify how said counter-ion in the EMPN can achieve charge neutrality.

Reaction equation examples for EMPN formation:

Reaction of tannic acid with 2 mole equivalents of FeCh and FeCh respectively, assuming that the average number of chelate-like bonds with every iron center is 2 (every Fe is coordinated with an average of 4 phenolate oxygens):

C76H₂7O2i(OH)25 + 2 FeCh + 2 FeCh+ 6 FAC1 [C76H27O2i(OH)₉Oi6Fe₄]FA6 + 16 HC1

Reaction of tannic acid with FeCh and TiCh respectively, assuming that the average number of chelate-like bonds with every iron center is 2 (Fe and Ti are coordinated with an average of 4 phenolate oxygens): C76H₂7O2i(OH)25 + 2 FeCl₂ + 2 TiCl₄+ 4 FAC1 [C76H27O2i(OH)₉Oi6Fe₂Ti2]FA₄ + 16 HC1

Reaction of tannic acid with V⁵⁺ and V⁴⁺ respectively, assuming that the average number of chelate-like bonds with every iron centre is 2 (V is coordinated with an average of 4 phenolate oxygens):

C76H₂7O21(OH)25 + 2 V⁵⁺ + 2 V⁴⁺ + 18 Cl [C₇6H27O21(OH)₉O16V₄]C12 + 16 HC1

The examples show that the resulting EMPNs have a net positive charge which needs to be balanced with anionic counter ions.

Below is also a general formula describing the reaction of one metal salt with tannic acid:

C76H27C>21(OH)25 + X MCly + (XZ-Xy) FAQ —> [C76H27O21(OH)(25 -xz) OxzM_x]FA_{xz xy} + xz HC1 in which: x = mole equivalents of metal ions per mole of tannic acid y = effective oxidation state of the metal (example 1 : 1 ratio of Fe(II) and Fe(III) would have an effective oxidation state of 2.5) z = average number of metal- oxygen coordinative bonds in the network.

Schematic 1 also assist to visualise a general structure of the EMPNs depicted by the example of polyphenol-iron complexes demonstrating changes in the overall charge of the metal phenolic complex requiring opposite charge of the counter ion depending on the extent of metal intercalation with oxygen anion.

Schematic 1 - general structure of the EMPNs depicted by the example of polyphenol-iron complexes.

In some embodiments, the counter-ion is selected from a metal counter-ion, an organic counter-ion, and a combination thereof.

In some embodiments, the counter-ion is an organic counter-ion.

An "organic" counter-ion will be understood to be an ion which chemical structure contains at least one carbon atom. In some embodiments, the organic counter-ion is a fluorinated ionic polymer, a fluorinated non-ionic polymer, a polyol, or a polyacrylic. In some embodiments, the counter-ion is an organic counter-ion selected from formamidinium, guanidinium, ethidium, tetrabutylammonium, imidazolium, phosphonium, sulfonium, pyrrolidinium, pyridinium, polyethyleneimine, polyallylamine, polylysine, poly[(l-vinyl-3- ethylimidazolium), Poly[(n-methyl pyridinium) salts, zwitterions like 2-(tert-butoxy)-N-(2- (methacryloyloxy)ethyl)-N,N-dimethyl-2- oxoethanaminium, functionalized ammonium salts like dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, functionalized polyamidines and polysunccinmides, cationic organic dyes (e.g. methylene blue), and a mixture thereof.

Achievable conductivity of the final product can vary based on the structure of the counterion. For example, use of guanidinium as counterion may afford final thin film conductivity of orders of magnitude lower than that of using formamidinium cation. In some embodiments, the counter-ion is a metal counter ion. For example, the counter-ion may be selected from Zn²⁺, B³⁺, Be²⁺, Mg²⁺, Cs¹⁺, Li¹⁺, Ca²⁺, Ba²⁺, Al³⁺, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Sc²⁺, Y²⁺, Ti²⁺, Zr²⁺, v²⁺, Nb²⁺, Ta²⁺, Cr²⁺, Mo²⁺, W²⁺, Mn²⁺, Re²⁺, Fe²⁺, Ru²⁺, Os²⁺, Co²⁺, Rh²⁺, Ir²⁺, Ni²⁺, Pd²⁺, Pt²⁺, Cu²⁺, Ag²⁺, Au²⁺, Zn²⁺, Cd²⁺, B²⁺, Al²⁺, Ga²⁺, Si²⁺, Sn²⁺, Pb²⁺, Hg²⁺, AS²⁺, Te²⁺, La²⁺, Ce²⁺, Pr²⁺, Sm²⁺, Gd²⁺, Nd²⁺, Db²⁺, Tb²⁺, Tm²⁺ and Yb²⁺ Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, and a combination thereof.

In some embodiments, the counter-ion is a metal oxide ion. Suitable examples in that regard include VO²⁺ and VO⁺.

In some embodiments, the counter-ion is a polycation. By "polycation" is meant herein a molecule having two or more cationic sites. Suitable examples of polycations for use in the EMPN of the invention include polyethyleneimine, polyallylamine, polylysine, poly[(l- vinyl-3-ethylimidazolium), Poly[(n-methyl pyridinium) salts, zwitterions like 2-(tert- butoxy)-N-(2- (methacryloyloxy )ethyl)-N,N-dimethyl-2- oxoethanaminium, functionalized polyamidines and polysunccinmides, poly(styrenesulfonate).

Examples of suitable polycations salts are also shown in Schematic 2 below.

Schematic 2 - Examples of a polycation salt which may be used as counter-ions. Where NTF2 corresponds to (bis(trifluoromethane)sulfonimide)

In some embodiments, the EMPN comprises a functional silane. Suitable examples of functional silanes include monofunctional and polyfunctional, mono or poly methoxysilanes. Accordingly, in some embodiments the EMPN comprises at least one of a monofunctional and bifunctional trimethoxysilane.

In some embodiments, the EMPN further can form molecular or non-molecular composites with organic non-conducting polymers like polymethyl methacrylate, polycarbonate, polyvinyl chloride, polyester, polyvinyl acetate, polyvinyl alcohol etc. in powder or solid state.

In some embodiments, the EMPN further comprises a conductor or semiconductor.

For example, the EMPN may comprise an organic conductor or semiconductor. In this context, an organic "conductor" would be understood to encompass organic compounds showing electrical conductivity or semi-conductivity. Typically, organic conductors used in the invention would have an electrical conductivity of at least 10~⁷S/cm. By the conductor being "organic", the conductor has a chemical structure that includes at least one carbon atom. Presence of the organic conductor or semiconductor facilitates charge mobility within the EMPN, resulting in an improvement of its electrochemical characteristics.

Examples of suitable organic conductors for use in the EMPN of the invention include intrinsically conducting polymers (ICPs), such as poly (3, 4-ethylenedioxy thiophene) (PEDOT)), poly aniline, their pyrolyzed analogues and inorganic conductors such as graphite, graphene, reduced graphene oxide (rGO), carbon black, carbon nanotubes (CNTs) inorganic polymers, carbonyl iron, MXenes and their pyrolyzed analogues

In some embodiments, the organic conductor is an ICP selected from a polythiophene, a polypyrrole, a polyaniline, a polycyclic aromatic polymer or copolymer thereof, and a mixture thereof. The term "polycyclic aromatic" refers herein to compounds having more than one aromatic ring. The rings may be joined by one or more bonds, or they may be fused together. The term "aromatic ring" is intended to include hetero aromatic rings. A "polycyclic heteroaromatic" compound has at least one heteroaromatic ring. In some embodiments, the organic conductor is selected from polydioxythiophene, poly aniline, polypyrrole, poly(thienothiophene), a copolymer thereof, and a mixture thereof. In some embodiments, the organic conductor comprises poly (3, 4-ethyenedioxy thiophene) (PEDOT) or a combination thereof.

In some embodiments, the ICP is a substituted ICP. Exemplary substituents include groups such as alkyl (-R)l aryl (-Ar), alkoxy (-OR), hydroxy (-OH), alcohol (-ROH), carboxylate (-RCO2H or -RCO2M, M= alkali or alkaline earth metal), and sulfonate (-RSO3H or - RSO3M).

In some embodiments, the organic conductor comprises graphene. The term “graphene” is used to indicate an allotrope of carbon having a one-atom thick planar sheet structure of typically sp²-bonded carbon atoms that are densely packed in a honeycomb two-dimensional crystal lattice. The covalently bonded carbon atoms typically form repeating units that comprise 6-membered rings but can also form 5-membered rings and/or 7-membered rings. A layer of such covalently bonded carbon atoms is commonly referred to as a graphene "sheet". Owing to the thickness in the order of atoms, graphene has a high surface area-to- volume ratio and high elasticity.

For the purpose of the invention, graphene may be synthesised according to any procedure known to the skilled person, for example known top-down or bottom-up synthesis procedures. Top-down procedures include, for example, micromechanical cleavage of graphite, mechanical or micromechanical exfoliation of graphite, electrochemical exfoliation of graphite, graphite intercalation, sonication nanotube slicing, ball milling, radiation-based methods, pyrolysis, and reduction of graphite oxide. Bottom-up approaches include, for example, growth of graphene from metal-carbon melts, chemical vapor deposition from C-containing gases on catalytic metal surfaces, graphitization of hexagonal SiC crystals during annealing at high temperatures under vacuum conditions, dry ice method, supersonic spray, and electron beam irradiation. In some embodiments, the organic conductor comprises reduced graphene oxide (rGO). The term "rGO" refers herein to a reduced form of graphene oxide. “Graphene oxide” (or “GO”) refers to a compound of carbon, oxygen and hydrogen obtained by oxidizing graphite, in which oxygen-containing groups are attached to the basal plane of stacked graphene sheets. Accordingly, "rGO" will be understood to be the compound resulting from at least partially reducing GO to eliminate at least a fraction of the oxygen-containing groups. For example, suitable rGO for use in the EMPN of the invention is rGO obtained by at least partially reducing GO by eliminating less at least about 25 %, at least about 50 %, at least about 75 %, at least about 90 % of the oxygen-containing functional groups of the GO.

When the EMPN is doped with an organic conductor, the organic conductor would be typically blended at a molecular level (<5 %) within the cations/-polyphenol coordination framework of the EMPN.

Alternatively (or additionally), an organic or inorganic conductor may also be used as a discrete entity in combination with the EMPN to form a molecular or non-molecular composite structure. Accordingly, certain aspects of the invention also relate to a composite comprising a EMPN of the kind described herein in electrical contact with an organic conductor of the kind described herein. By the EMPN and the organic conductor being in "electrical contact", electrical charges can travel from one to the other. Accordingly, provided charges can travel between the EMPN and the organic conductor, the EMPN and the organic conductor may or may not be in physical contact. In some embodiments, the composite comprises the EMPN on an organic conductor which is provided in film form. In those instances, the EMPN itself may or may not be provided in film form.

In its dry form the EMPN of the invention may present as a powdery substance. The EMPN can be dispersed to some extent in a range of solvents or can form a colloidal solution in solvents. Suitable solvents in that regard include polar solvents, such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), water, alcohol based solvents, pyridine based solvents, methyl ethyl ketone, dimethyl acetamide, N,N '-Dimethylpropyleneurea (DMPU), n-methyl- 2 -pyrrolidone, dimethylacetamide. By modulating the amount of solvent, the EMPN can be provided in forms that can range from a kneadable, self-supporting paste to a liquid or colloidal solution.

When in the form of a kneadable, self-supporting paste, the EMPN can be directly deposited in its bulk form on a suitable substrate by mechanically applying the paste onto the desired substrate. As such, the EMPN of the invention can be readily implemented into a device without requiring complex deposition systems.

When in liquid solution/dispersion form, the EMPN of the invention can be solution- processible. Advantageously, solutions/dispersions containing the EMPN of the invention can be used to deposit the EMPN onto a surface of suitable substrates in film form. This may be achieved in accordance with any wet deposition procedures known to a skilled person, which typically involve the deposition of a layer of the liquid solution onto a surface followed by solvent removal. For example, a liquid solution of EMPN may be used to deposit a film of EMPN on a surface of a substrate by spin-coating, dip-coating, knife-coating, spraycoating, meniscus coating, etc.

The EMPN of the invention is an electrically conductive material. The expression "electrically conductive" is used herein in a broad sense to encompass conductivity and semiconductivity. Compared to conventional metal-polyphenol coordination compounds, such as conventional Fe^IIZ-tannic acid coordination compounds, the EMPN of the invention has significantly enhanced electrical conductivity thanks to the inclusion of coordinated metal cations in different oxidation states. Typically, the EMPN of the invention would have an electrical conductivity of at least 10’³ S/cm. In some embodiments, the EMPN has an electrical conductivity of at least about 10’² S/cm, at least about 10 ¹ S/cm, at least about 10 S/cm, or at least about 100 S/cm. In some embodiments, the EMPN has an electrical conductivity of up to 1,000 S/cm, corresponding to an electrical resistivity of down to 10’³ ohm/cm.

The EMPN of the invention may also be provided with para-magnetic characteristics. As a person skilled in the art would know, a material having "para-magnetic" characteristics is one that is weakly attracted by an externally applied magnetic field, and form internal, temporarily induced magnetic fields in the direction of the applied magnetic field. Using a magnetic susceptibility balance a magnetic moment of 6.73 B.M was calculated for iron based EMPN.

The present invention also relates to a method of making an amorphous Cation-Organic Framework (EMPN) of the kind described herein.

The method comprises a step a) of combining at least one metal cation source and the polyphenol in a solution.

As used herein, the term "metal cation source" refers to a compound which can dissociate in ionic form to provide a cation of formula Mⁿ⁺, in which M is a metal element of the kind described herein, and n is an integer between 1 and 8. For example, Mⁿ⁺ may be Fe⁶⁺, Fe⁴⁺, Fe³⁺, Fe²⁺, Fe⁺, Cu⁴⁺, Cu³⁺, Cu²⁺, Cu⁺, Li⁺, Rb⁺, Cs⁺, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Sc³⁺, Sc²⁺, Sc⁺, Y³⁺, Y²⁺, Y⁺, Ti⁴⁺, Ti³⁺, Ti²⁺, Zr⁴⁺, Zr³⁺, Zr²⁺, Hf⁴⁺, Hf³⁺, V⁵⁺, V⁴⁺, V³⁺, V²⁺, Nb⁵⁺, Nb⁴⁺, Nb³⁺, Nb²⁺, Ta⁵⁺, Ta⁴⁺, Ta³⁺, Ta²⁺, Cr⁶⁺, Cr⁵⁺, Cr⁴⁺, Cr³⁺, Cr²⁺, Cr⁺, Cr, Mo'⁴, Mo⁵⁺, Mo⁴⁺, MO³⁺, MO²⁺, MO⁺, MO, W⁶⁺, W⁵⁺, W⁴⁺, W³⁺, W²⁺, W⁺, Mn⁷⁺, Mn⁶⁺, Mn⁵⁺, Mn⁴⁺, Mn³⁺, Mn²⁺, Mn⁺, Re⁷⁺, Re⁶⁺, Re⁵⁺, Re⁴⁺, Re³⁺, Re²⁺, Re⁺, Ru⁸⁺, Ru⁷⁺, Ru⁶⁺, Ru⁴⁺, Ru³⁺, Ru²⁺, Os⁸⁺, Os⁷⁺, Os⁶⁺, Os⁵⁺, Os⁴⁺, Os³⁺, Os²⁺, Os⁺, Os, Co⁵⁺, Co⁴⁺, Co³⁺, Co²⁺, Co⁺, Rh⁶⁺, Rh⁵⁺, Rh⁴⁺, Rh³⁺, Rh²⁺, Rh⁺, Ir⁶⁺, Ir⁵⁺, Ir⁴⁺, Ir³⁺, Ir²⁺, Ir⁺, Ir, Ni³⁺, Ni²⁺, Ni⁺, Ni, Pd⁶⁺, Pd⁴⁺, Pd²⁺, Pd⁺, Pd, Pt⁶⁺, Pt⁵⁺, Pt⁴⁺, Pt³⁺, Pt²⁺, Pt⁺, Ag³⁺, Ag²⁺, Ag⁺, AU⁵⁺, AU⁴⁺, AU³⁺, AU²⁺, AU⁺, Zn²⁺, Zn⁺, Zn, Cd²⁺, Cd⁺, Hg⁴⁺, Hg²⁺, Hg⁺, B³⁺, B²⁺, B⁺, Al³⁺, Al²⁺, Al⁺, Ga³⁺, Ga²⁺, Ga⁺, In³⁺, In²⁺, In¹⁺, Tl³⁺, Tl⁺, Si⁴⁺, Si³⁺, Si²⁺, Si⁺, Ge⁴⁺, Ge³⁺, Ge²⁺, Ge⁺, Ge, Sn⁴⁺, Sn²⁺, Pb⁴⁺, Pb²⁺, As⁵⁺, As³⁺, As²⁺, As⁺, Sb⁵⁺, Sb³⁺, Bi⁵⁺, Bi³⁺, Te⁶⁺, Te⁵⁺, Te⁴⁺, Te²⁺, La³⁺, La²⁺, Ce⁴⁺, Ce³⁺, Ce²⁺, Pr⁴⁺, Pr³⁺, Pr²⁺, Nd³⁺, Nd²⁺, Sm³⁺, Sm²⁺, Eu³⁺, Eu²⁺, Gd³⁺, Gd²⁺, Gd⁺, Tb⁴⁺, Tb³⁺, Tb²⁺, Tb⁺, Db³⁺, Db²⁺, HO³⁺, Er³⁺, Tm⁴⁺, Tm³⁺, Tm²⁺, Yb³⁺, Yb²⁺, or Lu³⁺.

For example, the metal cation source may be a salt of at least one cation of the kind described herein. The salt may be a salt of formula (Mⁿ⁺)_p(A^p’)n, wherein Mⁿ⁺ represents a cation as defined herein, and A^p“ represents an anion with p being 1 , 2, or 3. Regarding the selection of a suitable salt, the cation of the salt is essential. Suitable anions A^p_ include fluorine, chlorine, bromide, sulfate, nitrate, iodine, sulfate, nitrate, etc. Example of suitable salts therefore include A1₂(SO₄)3, Fe(SO₄), Fe₂(SO₄)₃, ZnSO₄, CuSO₄, CaSO₄, A1C1₃, FeCl₂, FeCh, ZnCl₂, CuCl₂, FeF₃, FeBr₃, Fel₂ Mg(NO₃)₂, Ca(NO₃)₂, CaCl₂, MgSO₄. Additional exemplary salts include acetates, formates, propionates, borates, haloborates, cyanoborates, trifluoromethanesulfonates, trifluoromethanesulfonimides, phosphates, and halophosphates.

In some embodiments, the at least one metal cation source comprises a chloride anion, a bromide anion, a sulphide anion, a iodide anion, or a hydroxide anion. In some embodiments, the at least one metal cation source comprises a nitrate salt, a sulphate salt, an acetate salt, a formate salt, a propionate salt, a borate salt, a haloborate salt, a cyanoborate salt, a trifluoromethanesulfonate salt, a trifluoromethanesulfonimide salt, a phosphate salt, or a halopho sphate salt.

Provided the resulting EMPN is an EMPN in accordance with the invention, there is no limitation to the number of salts used as the cation source. For example, the metal cation source may comprise at least two different salts, at least three different salts, etc.

In some embodiments, one metal cation source is used in step a), and the metal cation derives from that metal cation source.

In some embodiments, the metal cation source is two different salts. The two different salts may be selected from the salts described herein.

In some embodiments, the metal cation source comprises two salts, each of a different metal cation.

When the metal cation source comprises two salts of different metal cations that can have the same oxidation state (e.g. 2+), the nature of the cations can be selected based on their relative redox potential to ensure they coordinate to the polyphenol in different oxidation state. In particular, the metal cations should be selected to have sufficiently different redox potential to ensure one of the two cations can be oxidised preferentially when the cations are coordinated by the polyphenol. This will ensure the resulting EMPN has two cations with different oxidation state.

In some embodiments, the metal cation source comprises two salts, each of a different metal cation. EMPN conductive thin films were prepared using Fe²⁺/Cu²⁺, Co²⁺/Ni²⁺, Cu²⁺/Ru²⁺, Ni²⁺/Cu²⁺. In such examples, the metal cation source comprises two salts of different metal cations that can have the same oxidation state (e.g. 2+), the nature of the cations can be selected based on their relative redox potential to ensure they coordinate to the polyphenol in different oxidation state. However, in invention is not limited to these examples.

In some embodiments, the metal cation source comprises two salts, each of a different metal cation, each cation having a different oxidation state. An example in that regard are salts of Fe³⁺ and Co²⁺.

In some embodiments, the metal cation source comprises three salts, each of a different metal cation, each cation having the same or different oxidation state.

The metal cation source may be present in the solution of step a) in any amount that is conducive to the cation/polyphenol coordination compound forming. In some embodiments, the metal cation source is present in the solution in an amount relative to the polyphenol according to M:PP of about 1: 1, or at least about 14:1, or at least about 30: 1 (molar).

The polyphenol may be present in the solution of step a) in any amount that is conducive to the cation/polyphenol coordination compound forming. In some embodiments, the polyphenol is present in the solution in an amount relative to the metal cation source of at least about PP:M = 1:30, at least about PP:M = 1: 14, or at least about PP:M = 1: 1 (molar).

The amount of polyphenol relative to the metal cation source may be tuned to obtain the desired composition of the final EMPN. Other considerations may be made by a skilled person when deciding the relative amounts of polyphenol and metal cation source, based on the target EMPN composition. For example, the ratio between polyphenol and metal cation source may be decided also based on the degree of subsequent deprotonation that one intends to perform, and/or to the relative amounts of first metal cation to the second metal cation resulting from the nature of the specific cations and their relative redox potential. A skilled person would be capable to design the reaction system having those considerations in mind.

In the method of the invention, the polyphenol is deprotonated to obtain a cation/polyphenol coordination compound, the cation/polyphenol coordination compound comprising the one or more metal cations. For avoidance of doubt, the term "deprotonation" is used herein in a broad sense to encompass any degree of deprotonation, including complete deprotonation. Accordingly, step a) of the method may be understood to mean that the polyphenol is at least partially deprotonated.

Deprotonation of the polyphenol may occur spontaneously to some degree, for example by the metal cation(s) displacing one or more proton(s) to form a polyphenol/metal chelate. In addition, deprotonation may be facilitated by managing the reaction to ensure deprotonation of the polyphenol is favoured.

In some embodiments, deprotonation is affected by heating the solution of metal cation source and the polyphenol. This may be performed at any temperature that is conducive to the polyphenol deprotonating at least partially. In some embodiments, deprotonation is effected at a temperature of at least 30°C, at least 50°C, at least 70°C, or at least 90°C and ambient pressure or high pressures of a closed vessel. In some embodiments, deprotonation of the polyphenol is effected at a temperature of about 30°C, about 50°C, about 70°C, about 90°C, about and 100°C under vacuum of a rotary evaporator or under pressure or under the influence of an electromagnetic radiation source to enhance the rate of reaction.

Deprotonation of the polyphenol may also be favoured by ensuring that any deprotonation product (e.g. an acid formed with the anion of the salt(s) used as the metal cation source) is efficiently removed from the reaction system. For example, if the metal cation source includes a chloride, hydrochloric acid would form as a deprotonation product. Removing hydrochloric acid from the reaction system is helpful to displace the deprotonation reaction towards higher degrees of polyphenol deprotonation. Accordingly, in some embodiments deprotonation is effected by removing an acid product of the deprotonation reaction from the reaction system.

Deprotonation of the polyphenol could also be enhanced using slightly basic conditions, possibly provided by using relatively basic solvents or slightly basic reaction environment.

In the context of the invention, deprotonation of the polyphenol can be controlled to achieve various degrees of deprotonation. Controlling the degree of deprotonation of the polyphenol advantageously allows to tune the composition of the final EMPN, as the number of available sites and their respective coordination number for cation chelation can be modulated. Accordingly, in some embodiments, deprotonation of the polyphenol results in deprotonation of at least about 25%, at least about 50%, at least about 75%, or at least about 90% of the hydroxy (-OH) groups of the polyphenol, expressed in terms of the % ratio of deprotonated -OH groups over initial number of -OH groups.

The composition of the EMPN may also be tuned by chemically controlling the degree and rate of reduction/oxidation of the metal cations in the reaction system. This may be achieved by any means known to a skilled person. For instance, a reduction agent or an oxidation agent may be added to the reaction system. Accordingly, in some embodiments the method comprises adding a reduction agent or an oxidation agent in at least one of steps a) and b). A skilled person would know how to select and use reduction agents or oxidation agents for the purpose of controlling the degree of reduction/oxidation of the metal cations in the reaction system.

Examples of suitable reduction agents for use in the method of the invention include LiAlH4, NaBH₄, LiH, NaH, CaH₄, salts of Ba²⁺, Ca²⁺, or Cr²⁺.

Examples of suitable oxidation agents for use in the method of the invention include NOBF₄, H2O2, HN0₃, H₂SO₄, F₂, CI2, MnO₄, Au⁺¹, Co³⁺. The reduction agent or the oxidation agent may be used in any amount that affords the intended degree of reduction or oxidation of the relevant cation, respectively. Typically, the amount of reduction agent or oxidation agent would be determined relative to the amount of metal cations in the reaction system. In some embodiments, the relative amount of reduction agent (or oxidation agent) and metal cation source is at least about the stochiometric amounts or at least about 2%.

As the polyphenol deprotonates, the deprotonated sites coordinate the metal cations deriving from the metal cation source. Depending on the nature of the cations and of the degree of deprotonation, the polyphenol may coordinate the cations having different oxidation states.

For instance, and without wanting to be limited by theory, it is believed that if the metal cation is of one kind only, the availability of mono-, di-, tri- tetra- etc. chelating sites in the deprotonated polyphenol may force the reduction/oxidation of the cation according to the coordination number of the available chelating site, resulting in the metal cation coordinating at different coordination sites having different oxidation state. Conversely, if there are two kind of metal cations in the reaction system, it is believed they will coordinate to the available chelating sites in accordance with their relative oxidation state (if natively different) or be oxidised/reduced to assume different oxidation states depending on their relative redox potential.

The method of the invention also includes a step b) of combining the cation/polyphenol compound with a counter-ion salt in a solution to obtain the EMPN. This may be achieved, for example, in a vapour, solution, gel, or solid state.

The counter-ion salt used in step b) may be any salt that can be provided in a solution/dispersion with the metal polyphenol network. For example, the counter-ion salt may be a salt of a counter-ion of the kind described herein. For example, the counter-ion salt may be a metal or an organic salt. In some embodiments, the counter-ion salt is a metal salt selected from LiTFSI, LiOTf, NaTFSI, KI, KBr, CsI, CsBr, RbBr, FrBr, or LiF.

In some embodiments, the counter-ion salt is an organic salt selected from a salt of formamidinium bromide, guanidinium bromide, ethidium bromide, tetrabutylammonium bromide, imidazolium bromide, polyethyleneimine bromide, polyallylamine bromide, polylysine bromide, poly [(1 -vinyl- 3 -ethylimidazolium) bromide, or iodide, fluoride, chlorides salts of the respective compounds, and a mixture thereof.

In some embodiments, the counter-ion salt is selected from formamidinium, guanidinium, ethidium, tetrabutylammonium, imidazolium, polyethyleneimine, polyallylamine, polylysine, polyvinylimidazolium poly[(l-vinyl-3-ethylimidazolium), a fluorinated ionic and non-ionic polymer, a polyol, and a polyacrylic.

The amount of counter-ion salt used in step b) may be any salt that is conducive to formation of a charge-neutral EMPN. In some embodiments, the counter-ion salt is used in the solution of step b) at a concentration of from about (metal/counter ion: 1/1) to about (metal/counter ion: 1/10). The counter-ion salt may be used in any amount relative to the amount of cation/polyphenol compound that is conducive to formation of a charge-neutral EMPN. For instance, the amount of counter-ion salt to cation/polyphenol compound may be from about 50 : 1 to about 10 : 1. In some embodiments, the counter-ion salt and the metal cation source are used to provide the same molar equivalents.

Step b) may be performed at any temperature conducive to the EMPN forming. In some embodiments, step b) is performed at a temperature of at least at least about 0°C, at least about 25°C, 50°C, 70°C, or at least about 90°C and ambient pressure or high pressures of a closed vessel. In some embodiments, step b) is performed at a temperature of about 0°C, about 25°C, about 50°C, about 75°C, or about 100°C, under the vacuum condition of a rotary evaporator or under the influence of an electromagnetic radiation source to enhance the rate of reaction. In some embodiments, step a) and/or step b) comprise(s) heating the solution to a temperature of at least 25°C.

In addition, step b) may have any duration conducive to the EMPN forming. In some embodiments, step b) is performed for at least about, 1 minute, 1 hour, at least about 5 hours, at least about 10 hours, at least about 1 day, or at least about 10 days.

In some embodiments, the method further comprises a step c) of adding an organic conductor or semi-conductor to the EMPN. Said organic conductor or semi-conductor may be an organic conductor or semi-conductor of the kind described herein.

In a typical synthesis the first step is to react one or several types of polyphenols with one or several metal salts. This reaction typically takes place in a solvent which can either fully or partially dissolve all starting materials. Typical solvents comprise water, ethanol, methanol, DMF, DMSO or mixtures thereof. The molar ratio in which the PPC and metal salts are added is variable. In a typical synthesis the molar ratio of phenolic groups to metal ions is within the range of 2: 1 to 100: 1. One possible way of inducing the reaction is via the slow addition of the metal salt solution to a PPC solution (or vice versa) under stirring. The product can also be formed via a solid-state reaction. One example of such a solid-state reaction would be to place the PPC compound(s) and the metal salt(s) into a ball mill and to mill them until the EMPN has formed.

Control of the synthesis parameters is important in order to obtain electrically conductive EMPNs. Parameters that need to be controlled are the rate at which the reagents are mixed, the reaction temperature, the pressure, and the rate at which volatile compounds from the reaction mixtures are transferred and removed from the reaction mixture. The reaction can also be assisted by the presence of microwaves.

The formation of the EMPN can be promoted by the presence or controlled addition of bases and/or the removal of acids. The base can also form in situ as a product of a chemical reaction taking place or can be introduced via the gas phase. The formation of the EMPN can also be promoted by the removal of acids. For example, if all or some of the metal salts used during the synthesis of the EMPN are halides, then the formation of the EMPN can be promoted by allowing hydrogen halide, which will form during the reaction, to outgas from the solution into the gas phase. This mechanism can be extended to any reaction where the reaction solution contains a base which can form a volatile acid. Examples comprise acetate, formate and propionate salts.

It can also be envisaged that additional compounds are added during this first synthesis step to help control the properties of the resulting EMPN. These additives may or may not be present in the final product. This also includes ionic compounds, including polycationic and/or poly anionic compounds. In some embodiments the EMPN is blended with at least one other material to form a composite material. The blending can occur during the actual synthesis of the EMPN or during the paste/ink formulation. This can result in blends that have improved electrical, mechanical or other properties such as ionic conductivity, affinity to other compounds or biological analytes and pathogens.

Examples of such materials are conducting and non-conducting polymers such as [poly (3,4- ethylenedioxythiophene) (PEDOT), polyaniline and polypyrrole or their monomers], nonconducting polymers such as [ethyl cellulose, polyethylene glycol, polyvinylpyrrolidone (PVP), polyacrylics, polyurethanes, polyesters, polytetrafluoroethylenes or their monomers], carbon allotropes such as carbon nanotubes (CNTs), graphene / reduced graphene oxide, carbon black and graphite, MXenes, metal nano or microparticles, carbonyl iron, pyrolyzed organic and inorganic polymers.

Depending on the nature of metal salt used for the synthesis of EMPN and the desirable size of EMPN NPs, slight variation can be made in the synthetic procedure, that includes reducing or removing the need for autoclave reaction.

The reaction product is a metal-phenolic network which presents itself as a suspension, colloidal solution or solid comprising the EMPN.

The EMPN obtained with the method of the invention may undergo post-synthesis processing. Post-synthesis processes can be applied with the goal to modify the general properties of the EMPN or with the goal to produce a formulation which is suitable for further processing steps, including coating, printing, and moulding processes.

Post-synthesis processes can help to further improve properties such as the conductivity of the resulting EMPN. One example for such a treatment is the addition of salts. Such salts comprise formamidinium salts, imidazolium salts as well as polycations and polyanions. The addition of such salts was observed to increase the conductivity of the final EMPN film after coating by several orders of magnitude.

Salt addition can be combined with washing steps. A washing step here is defined as a process where the solid component of the mixture is removed for example by centrifugation or filtration and then resuspended in solvent. Working steps including salt-addition and washing steps can also be described as ion exchange reactions.

Post-synthesis processes can also aim at altering the particle size, crystallinity. They can also involve processes which allow to separate the reaction product according to particle sizes and to thereby narrow the particle size distribution in the final product.

Post-synthesis steps can also include storage of the EMPN-containing reaction products for certain time periods with or without temperature control in closed or open vessels or in contact with a gas stream.

A convenient way of applying the electrically conductive EMPN is via film forming or coating processes, including but not limited to spray-coating, ink-jet printing, 3D-printing, brush-painting, blade-coating, spin-coating, slot-dye-coating, gravure coating, reversegravure printing and offset-printing. This requires the formulation of print media with properties that are adapted to the printing technology. This includes the rheological and wetting properties and the choice of solvents. Inks, pastes and solutions suitable for printing can be produced directly from the initial reaction product which presents itself as slurry, suspension or colloidal solution. Possible post-processing steps comprise centrifugation, filtration, addition of solvents or other compounds, removal of solvents via decantation or evaporation, resuspension, control of proton activity via the addition of acids or basis and exposure to gasses (including air) or gas flows.

The initially formed product comprising the EMPN can also be converted to a powder. This powder can be combined with solvents and other additives to form pastes and inks, suitable for printing and coating processes. Alternatively, the powder can be used directly for powder-based coating techniques or moulding processes to produce 3D objects.

Generally, additives can be added at any stage of the synthesis or post-synthesis process. This includes additives which themselves are electrically conductive. In this case a composite material is formed in which the intrinsic electrical conductivity of the EMPN is enhanced by blending it with another conductive material.

The purpose of additives can also be to alter the physical properties of the resulting film. The EMPNs generally form mechanically stable films which are well adherent on many types of surfaces even in absence of any additional binders.

The actual coating process can be followed by a drying and/or heating processes either at room temperature or at elevated temperature, which itself can also influence the electrical conductivity of the film.

The films or coatings can further be chemically processed by exposure to vapours or gases or solutions. This can also influence the film properties, including its electrical conductivity, specifically if this processing step involves redox active compounds or bases or acids.

The EMPN can also be used to coat any type of surface or material, including fabrics, yarns and fibres. For certain applications the final EMPN-comprising product can present itself as slurry, suspension, paste or colloidal solution. Such applications can include energy storage media applied in batteries, including redox flow batteries. Here the electrical conductivity of the EMPN particles can be beneficial during the storage and release of electrical energy.

The EMPN can be blended with other materials at any stage of the synthesis or during postsynthesis steps to form composite materials or films.

It is also feasible to fabricate membranes comprising EMPNs. Such membranes can either be free standing or located on a support substrate. The porous nature of the EMPN will enable ionic conductivity across the membrane while the electrical conductivity of the EMPN-comprising membrane can be used to alter the ionic conductivity of the membrane.

It can also be envisaged that a porous electrically isolating, ion-permeable support structure is coated on both sides with a layer of material comprising EMPNs to form a membrane-like structure.

For certain applications the final EMPN-comprising product can be a 3 -dimensional shape. In certain embodiments such shapes can be produced by 3D-printing or moulding.

Synthesis and post-synthesis steps need to be chosen carefully in order to obtain a final material which is electrically conductive. As general principles, conditions which promote the electrical conductivity of the final product include:

[1] The use of metal salts in different oxidation states, such as Fe(II) and Fe(III) compounds as starting materials or the use of salts of different elements such as iron and titanium salts favours the formation of electrically conductive EMPNs.

[2] Control of the reaction rate between the metal salt(s) and the polyphenols to form the EMPN can be critically important for the formation of electrically conductive EMPNs. More specifically, we have observed that slow reaction rates favour the formation of electrically conductive EMPNs. More specifically we observed that mixing of polyphenols and metal halides and a prolonged reaction time in a container open to the atmosphere can yield electrically conductive EMPNs.

[3] Control of temperature during the synthesis. In some cases, it can be advantageous to perform the synthesis under reflux conditions.

[4] The presence of redox-active compounds during the synthesis or post-synthesis steps. This includes oxygen from air.

[5] Post-processing steps aimed at controlling the chemical composition and the particle size of the resulting EMPNs. This includes conditions such as elevated temperature and or elevated pressure.

[6] Post-processing steps which change the chemical composition of the EMPN. This can include ion exchange reactions and the addition of bases or acids. This also includes the addition of compounds which have a chemical affinity to the EMPN, including ionic compounds or compounds capable of forming 7t-7t interactions with the EMPN.

[5] Reaction of the starting materials using a microwave reactor can also enhance the formation of EMPN.

Applications

The EMPN described herein can be implemented on a wide range of applications, thanks to an advantageous combination of high processability and tuneable electric properties.

For example, the EMPN of the invention may be effectively used as hole transport layer in photovoltaic s. In those instances, the EMPN of the invention could provide an efficient and significantly cheaper alternative to conventional polymeric and metal-oxide hole transport layers for in thin film photovoltaic cells. In addition, the EMPN of the invention may be used as an efficient electroactive material for electrode and/or electrolyte for solid-state energy storage devices, such as secondary or rechargeable batteries and supercapacitors, including thin film batteries and supercapacitors.

The EMPN of the invention may also find applicability as a highly sensitive chemi-resistive sensor, for example in thin film form, to detect trace amounts of gases such as ammonia, sulphur, CO, oxygen, nitrogen , nitrogen dioxide ethylene oxide, formaldehyde, hydrogen sulfide, methyl bromide, sulfur dioxide, sulfur mustard / 2-chloroethyl ethyl sulfide (CEES) or their molecular equivlents, organophospates, and as biosensor using enzyme embedding or viral and immunological detection.

In addition, the para- magnetic or ferromagnetic characteristics of certain EMPNs of the invention may be effectively implemented in electromagnetic or radiofrequency (EM) transmission or shielding coatings. The magnetic behaviour can even be manifested by a weak attraction of Fe-EMPN particles towards a Neodymium magnet block (30 x10 x 6 mm)

The EMPN of the invention can also find application as gas absorption material, due to its inherently high surface area. For example, the EMPN can be used to reversibly absorb gases, such as CO2, hydrogen, ammonia, sulphur, CO, oxygen, nitrogen, ethylene oxide, formaldehyde, hydrogen sulfide, methyl bromide, sulfur dioxide, sulfur mustard / CEES or their molecular equivalents. Advantageously, the absorption can be reversed by applying a simple external input to the EMPN, for example a temperature increases and/or an applied voltage.

Further applications for the EMPN of the invention may include thermoelectrics, moderately conductive thin coating products, transistors sensors, RF antenna and the like.

The intrinsic electrical conductivity of EMPNs enables their use in a number of applications where this electrical conductivity provides a clear advantage over similar, non-conductive materials or where the electrical conductivity is an essential prerequisite for its use in this application. Choice of metal centre for the fabrication of EMPNs can also influence characteristic properties of the film that includes but is not limited to the properties like, conductivity, absorption and reflection signature in the electromagnetic spectrum, thermal stability and various electrochemical properties originating from the metal to ligand interactions.

Examples of applications include the following.

Electrically Conducting Surfaces

Polyphenolic networks intrinsically offer unique functional groups that help in coating on most of the surface. Thus, a judicious control of extent of metal intercalation of polyphenol in combination with the secondary counter -ion like formamidinium bromide offers unique opportunities for producing electrically conducting coating on a wide variety of surfaces like metals, metal oxides, glass, fabrics, wool, carbon products, varieties of foams, gels, leather, wood, concrete, ceramics etc.

EMPN materials can be used to create electrically conducting coating, self-standing films, and patches; feedstock for 3D printed or die-cast coating, rolling and several similar techniques. A tertiary control on the properties of the EMPN can be exerted by covalent and non-covalent interaction of small molecules with EMPN materials that are intrinsically hierarchically porous and contain functional sites. On macro scale, EMPNs have highly functional nano and micro cavities that can offer sites for the formation of composites with particles on nano- and microscale.

Electromagnetic shielding

This also includes applications where the EMPN is to interact with electromagnetic radiation for the purpose of telecommunication, radar, detection, and camouflage where the ability of the EMPN to interact with such radiation is a direct or indirect consequence of its electrical conductivity. Electromagnetic shielding technique is used to reduce or completely block electromagnetic fields from entering a given space. We have shown that EMPN coatings show electromagnetic shielding effects. Possible applications include: a) packaging of electronic components b) cables c) vehicles including but not limited to cars, planes and drones d) buildings e) textiles and clothing f) large vessels under or on the surface of water

The functions of these coatings include but is not limited to protection of electronic components from electromagnetic interferences, protecting electronic components from damage that can be caused by electromagnetic radiations and the reduction of the exposure of the human body to electromagnetic radiation.

Electromagnetic shielding can be obtained simply by coating surfaces with a paint comprising the EMPN. This coating can be applied to plastic bags to protect electronic components during shipping, onto the housing of electronic components, or onto the outside or inside walls of a building or similar structure. The EMPN can also be applied to a fibre or fabric which itself is a component within a composite material. A Faraday -cage-like structure can then be constructed from such structural elements comprising this composite material. Electromagnetic shielding can also be achieved by creating an enclosed space with textiles, foils or canvases coated with EMPNs or made from EMPN-coated fibres or yams. This includes tarpaulins and tents.

EMPNs can also be applied as thin, semitransparent films to create coatings which provide electromagnetic shielding and allow for the partial transmission of selected parts of the electromagnetic spectrum.

EMPN-comprising wall paints can be formulated for the building industry to create electromagnetically shielded spaces and / or active materials for the smart wall fabrication. The EMPNs described here have several unique properties which make them attractive for such applications, including low cost, stability, excellent adhesion on many surfaces and the fact that they are environmentally benign.

Thin films of EMPNs show high electrical conductivities of up to 28 S-cm ¹ This conductivity can further be improved to 1000 S-cm ¹ by mixing of an EMPN suspension with EDOT (3, 4-ethylenedoxy thiophene) prior to the film formation. It can be assumed that the presence of Fe(III) in the EMPN promotes the polymerisation of EDOT to PEDOT.

Radar Absorbing Materials/camouflage

Coatings which comprise EMPNs can also be used to alter the way surfaces interact with or more specifically back-scatter radar signals. They can be blended into state-of-the-art stealth-coatings such as carbon, boron nitride materials or carbonyl iron compounds or alternatively constitute the main active component within the coating. Alternatively, the structural elements defining the outer shape of the object to be camouflaged can comprise the EMPN or materials which themselves are coated with the EMPN. It has been observed that fine-tuning of the absorption signature can be realized by judicious selection of various layers of the different metal centre based EMPN spray coatings.

Electrochemical converters and fuel cells

Electrochemical converters are becoming increasingly important. They allow to produce valuable materials, including fuels and other chemical feedstocks by means of electrical energy which itself can be obtained from renewable energy sources. This also provides a storage solution for electricity generated from renewable energy. Fuel cells on the other hand are electrochemical converters which can help to increase the efficiency of a converting chemical energy stored in fuels into electricity. Redox flow batteries on the other hand are another form of electrochemical converters which can be used to store and release electrical energy. Electrochemical converters contain electrodes made of electrically conductive materials which are in direct contact with an electrolyte. The main function of the electrodes is to facilitate the electrochemical conversion of components comprised in the electrolyte or gasses in contact with the electrode. The products of the electrochemical reaction themselves can be comprised in the electrolyte or represent a gas.

The environment inside electrochemical converters can be quite harsh in terms of the chemical environment, the corrosive nature of the media (electrolytes), and the temperature. Conventional metals are often subject to rapid corrosion under such conditions. Furthermore, the materials used as electrodes and electrocatalytic layers in such applications often require to have specific catalytic properties and/or have low overpotentials for the electrochemical reaction taking place. In certain cases, the material also needs to be designed to favour the desirable electrochemical reactions over electrochemical side reactions. In other cases, it can be of advantage if the electroactive material used in electrochemical converters features a high surface area.

EMPNs can be designed to be corrosion resistant and typically feature a high internal surface area. The high chemical tunability of EMPNs means that they can be designed to have intrinsic catalytic and or electrocatalytic properties. They can be used as either anode or cathode materials. EMPNs can also be blended with catalytic and/or electrocatalytic materials to form composites or blended electromaterials. These properties distinguish EMPNs as excellent materials to be used as electrode materials in electrochemical reactors.

The electrode material comprising the EMPN can be applied as a coating onto an insulating surface or on top of a compatible conductive material. Alternatively, an electrode can be envisaged which is a composite material comprising one or several EMPNs mixed or blended with a conductive material such as carbon nanotubes or graphite. Such a composite material can be free-standing or be applied as a coating.

In case that an EMPN containing coating is used as electrode it can be beneficial to apply this coating to a substrate which itself has a high surface area. Of particular interest are electrodes with hierarchical pore structure.

Electrical storage medium

EMPN films and coatings which are in contact with a liquid or solid electrolyte can be used as components for devices that can store electrical energy. Such storage devices typically require at least 2 electrodes, generally referred to as anode and cathode. Due to the high internal surface area of EMPN films such films are able to store energy in a similar fashion to a electrostatic double-layer capacitor. EMPN films can also store energy in a similar fashion to a battery, due to the redox activity of its components. EMPN films can be used either as anode or cathode or both. The electrical storage device might be for single use or rechargeable, so that it can undergo several charging and discharging cycles.

EMPN electrodes can be combined with any other electrode materials that are known to store electrical energy either as an electrostatic double-layer capacitor or as component in a redox battery or pseudocapacitor, including but not limited to lithium intercalation electrodes and high-surface area carbon-based electrodes. The design of the electrical energy storage device can assume any known architecture which has previously been described. Typically, the device also contains an ion-permeable membrane or separator to avoid electrical contact between the 2 electrodes.

EMPN coatings applied in electrical storage media such as batteries and supercapacitors can have several functions. While they can constitute the medium which is actively involved in the charge storage they can also be used primarily as charge collecting electrodes to enable the flow of electrical currents from the redox-active material to the external electrical contacts of the device and vice versa.

It can also be envisaged that the EMPN used in the electrical storage device is not a film but instead a slurry, suspension, colloidal solution or mouldable or heat-mouldable composite. This includes a composite material comprising the EMPN and a liquid or solid material capable of conducting ionic charge. Pressure can be applied to such composites to mold them, define their shape and improve the electrical and/or ionic conductivity or to laminate such material to another component of the device, such as an ion-selective, electrically insulating membrane.

EMPNs can also be used as active ingredient of electrolytes used in redox-flow batteries. In this case the EMPN can be the primary component, capable of storing electrical charge, or it can be combined with other redox-active components. Redox flow batteries typically contain at least 2 different electrolyte systems. Here the EMPN can be comprised in one or all redox electrolytes used. It can be envisaged that a redox electrolyte system containing a high EMPN mass fraction (> 5%, preferentially > 20%) have sufficient energy density to be applied in mobile transport applications.

EMPN-based electrodes are unlikely to suffer from dendrite formation and associated issues due to the fact that the metal-phenolic network will stay in shape and not dissolve and redeposit.

It can be envisaged that the ionic species present in the film, providing a counter balance to the overall charge of the EMPN also act as redox active components. Of particular interest are redox reactions where the reduction process produces a species that is less negative or positive and oxidation reactions which produce ions that are less positive or negative.

Example:

VO₂ ⁺ + e + 2 H₃O⁺ VO²⁺ + 3 H₂O

This can be combined with a reduction of a metal cation Mⁿ⁺ in the EMPN:

The use of redox active counter ions inside the EMPN can increase the achievable electrical storage density. Also, in the case above, when EMPN and counter ion reduction happen simultaneously the transfer of 2 negative charges to the EMPN-comprising electrode is accompanied by the transfer of 2 protonic charges (H⁺ or H3O⁺) from the electrode to the electrolyte. The ion mobility of protons is generally much higher than that of other ions. This and other factors can have a favourable effect on the charging/discharging speed.

An example for an electrical storage device comprising EMPNs is a device composed of a first electrode with an EMPN coating comprising Fe²⁺, Fe³⁺ and tannic acid and a second electrode comprising Ti⁴⁺, Ti³⁺ and tannic acid. The two electrodes are separated by an ion- permeable membrane. The gap between the 2 electrodes is filled with an electrolyte such as a 100 mmolar solution of EiOH in acetonitrile.

Ion absorption and desorption media

The storage and release of electrical charge in EMPNs is typically coupled with movement of equivalent amounts of ionic charges into or out of the electrical storages medium. This will enable the use of electrically conductive EMPNs for the selective absorption or release of ionic species or charged particles from liquids such as water. Such devices are typically referred to as capacitive deionisation devices (CDDs). Due to their high surface area and charge capacity EMPNs are very suitable materials to be used in CDDs.

CCDs can be used to create deionised water from saltwater, brackish water or otherwise contaminated water and it can also be used to extract and enrich valuable ions from dilute solutions. Applications considered here make use of the electrical conductivity of the EMPN. Applications can either use the EMPN in a single use or be designed to undergo multiple cycles.

Typically, capacitive deionization devices use pairs of carbon electrodes. Both electrodes are contacting the ion-containing medium and deionisation is driven by application of an external electrical potential difference. The ions can then be released by applying a time- controlled reverse bias or by short-circuiting the 2 electrodes Asymmetric electrode configurations for CDDs can be envisaged. This can be achieved by combining 2 EMPNs with similar chemical composition but differences in the redox states of the contained ions. CDD devices can also be envisaged with two chemically different EMPNs, such as one EMPN made from iron ions and another EMPN made of titanium ions. Alternatively, an EMPN electrode can be combined with a non-EMPN electrode (for example an electrode made of carbon material). The electrochemical potential difference between the two electrodes can drive current flow between those electrodes and therefore also ion migration to or from those electrodes.

For some applications ion selectivity is an important attribute of EMPNs, such as for example for the extraction of specific ions from liquids containing at least one other ion. Due to their chemical tunability, as well as the tunability of their porosity, specifically on the nm range such materials such materials can easily be tuned to achieve ion selectivity. Ion selectivity can either be achieved during the ion adsorption process or due to differences in their desorption behaviour. This can be applied in cases when valuable ions need to be extracted from dilute solutions, such as the recovery of lithium from seawater or when ions need to be removed from liquids due to their toxicity or harmful effect on the environment, such as lead from industrial wastewater.

When using at least one cycle, combining an ion adsorption process with an ion desorption process either both or only one of the processes can be actively driven by application of a potential between the two electrodes. In certain applications the electrically driven ion adsorption or desorption can be combined with simultaneous or subsequent ion exchange reactions.

Ion release and capture can also be controlled through the concentration and nature of ions contained in the EMPN. Charged species(ions) can also be covalently linked with the EMPN, i.e. via a covalent ester bond to some of the phenolic hydroxy groups in the EMPN. This modification can be performed before or after the reaction of the polyphenol with the metal ions to form the EMPN. EMPN electrodes can also be used for the electrically-controlled release of ions i.e. in a medical device (drug delivery) or for the electrically-controlled release of fertiliser (agriculture).

Sensors

The electrically conductive EMPNs are particularly interesting for sensing applications where the electrical conductivity or resistivity of an EMPN film or an array of EMPN films is monitored over time to detect an analyte. The sensor can either be exposed to a gas phase such as atmospheric air or a liquid phase. The EMPN has a high degree of tunability in terms of its chemical nature and its porosity. It can also be blended with other compounds that interact with or have an affinity to the analyte or biological agent to be detected. The sensor will be particularly sensitive to analytes which are redox active or carry redox active sites and therefore can directly affect the charge transport properties of the EMPN. Alternatively, the redox state (paramagnetic property) of the EMPN metal ions can be locally probed indirectly by observing the fluorescence properties of nearby fluorophores, such as nitrogenvacancy colour centres in diamond.

Electrical read-out sensors can be produced by coating a layer comprising an EMPN onto an array of interdigitated electrodes located on a substrate. Such sensors can be operated in the gas phase or a liquid phase. It can also be envisaged that the EMPN-containing sensor is part of a larger sensor array. It is also possible to build a sensor array with several independent sets of interdigitated electrodes co-located on the same substrate with different variants of EMPNs printed onto these electrodes.

Thermoelectric applications

We have observed thermoelectric effects for EMPNs which can be used for converting thermal energy into electricity or to construct an electrical device for cooling or heating purposes. Preferentially the thermoelectric device contains 2 EMPNs which differ in their chemical composition. Bioelectronic interfaces

We have observed nerve cell growth on top of the surface of EMPNs, providing evidence that such materials are biocompatible and can be suitable materials for bioelectronic interfaces.

Touch-sensitive surfaces and proximity sensors

Extremely thin film of EMPN materials on an interdigitated Au electrode shows change in the resistance upon the proximity of human hand. Such changes in the resistance arises from local capacitance changes. This property of the EMPN materials can be used to fabricate printable proximity touch sensors.

Corrosion protection

EMPN materials are highly functionalized materials and are very ideal to coat activated metal surfaces in order to achieve a covalent bonding to the surface and stop from corrosion. In order to evaluate the effectiveness of our coatings we have selected magnesium alloy as substrate that is prone to high corrosion rate. The initial results have been extremely successful.

Super-hydrophobic electrically conducting coatings

As the starting materials for the synthesis of EMPN materials are polyphenol which are generally hydrophilic and this hydrophilic character is still dominant upon the formation of final EMPN films, however, a tertiary control which is exercised by the reaction of EMPN materials with small molecules like silanes can induce a super-hydrophobic character to the EMPN films. By exerting this tertiary control on the physiochemical properties of the EMPNs, we have fabricated super-hydrophobic, electrically conducting films that show outstanding stability. The invention is also described with reference to the following non-limiting examples.

EXAMPLES

Materials and Methods

Unless otherwise stated, all reagents and chemicals were used as received from Sigma Aldrich, Australia.

Field-Emission Gun Scanning electron microscopy (FEG-SEM) images were recorded with an FEI Nova NanoSEM 450 FEGSEM with an operation voltage of 10 kV. The samples were coated on fluorine doped tin oxide glass substrate without any extra conducting particles coating.

Surface analysis of the EMPNs was performed by nitrogen sorption isotherms at -196°C using a micrometrics 3Flex system. The surface area and pore size distributions were estimated by using the Brunauer-Emmett-Teller (BET) equation and the Barrett- Joynfer- Halenda (BJN) method, respectively.

UV/VIS spectra were recorded with a Lambda 950 Perkin-Elmer spectrophotometer, using the standard detector for liquid measurements and an integrating sphere for solid-state measurements.

X-ray photoelectron spectroscopy (XPS) was operated on a Nexa Surface Analysis System (Thermo Scientific).

Hydrodynamic size of the particles was measured using light scattering measurements performed using a Malvern Zetasizer Nano ZS. All the measurements were carried out at room temperature. A Keithley 2400 source meter was used to record the IV-characteristics of thin film coatings on interdigitated electrodes and Jandel Multiheight Probe RM3000 was used to measure the sheet resistance of thin film coatings.

EXAMPLE 1

Synthesis of EMPN

Tannic acid (50-500 mmol) was dissolved in isopropanol (IPA) on heating. FeCh, FeCh or an appropriate mixture of FeCh and FeCh (0.5 - 6 moles) was separately dissolved in IPA, water or appropriate mixture of water and IPA and both solutions were mixed at 70 degree Celsius. The bluish mixture was heated at 70-100 °C, with open lid for several hours to get rid of HC1 by-product. Removal of HC1 can be enhanced using rotary evaporator. The mixture was closed in a large Schott bottle and placed on hot plate for several hours at 70 degree Celsius, or alternatively in an autoclave reaction vessel at around 100 °C, for 2 - 48 h to obtain ion-tannic acid coordination complex (FeTA) solution product or using a microwave reactor. In order to straightaway obtain a final conductive suspension or colloidal solution of FeTAFABr ink, 0.5 - 30 moles of formamidinium bromide (FABr) were dissolved in IPA and reacted with FeTA solution product.

However, in order to harvest FeTA particles, FeTA solution product was cooled down to room temperature and successive washing was carried out using IPA, diethyl ether and toluene. Blackish particles of FeTA were obtained by centrifuging at around 6,000 rpm and were dried for further reactions.

In a separate Schott bottle, 0.5 - 30 moles of formamidinium bromide (FABr) were dissolved in IPA and reacted with FeTA particles product of last reaction. Reaction was carried out at 70-100 degree Celsius for several minutes to several hours in IPA, water, DMSO or appropriate mixture of these solvents with FABr. Reaction product obtained by either of the above stated methods was allowed to cool down to room temperature. Larger particles were separated by centrifuge and supernatant in IPA was saved for direct thin film application. Larger particles were repeatedly washed using IPA, diethyl ether and toluene or either of the solvents to achieve final product FeTAFABr NPs.

EXAMPLE 2

Equimolar amounts of FeCh and FcCE are dissolved in IPA or water. Tannic acid is dissolved in IPA or water separately. The iron chloride solution is then added dropwise to the tannic acid solution under stirring. The mixture is then kept under reflux conditions for several hours to allow for the partial or complete transfer of the reaction by-product HC1 to the gas phase. The reaction product, comprising the EMPN is harvested by a process involving a centrifugation step, decanting and subsequent resuspension in an alternative solvent. In this example the reaction product is washed twice with diethyl ether followed by resuspension in isopropyl alcohol. Subsequently a solution of formamidinium chloride (1- 10 molar excess to Fe) is added and the reaction mixture is left to react for several hours. The resulting reaction product, comprising the EMPN can then be used to produce thin films via a blade coating and subsequent drying process.

EXAMPLE 3

Tannic acid (500 mmol) was dissolved in isopropanol (IPA) on heating, NiCh (5 mol) was separately dissolved in IPA water or appropriate mixture of water and IPA and both solutions were mixed at 70 degree Celsius. The yellowish mixture was heated at 70 °C with open lid for several hours to get rid of HC1 by-product. The mixture was closed in a large Schott bottle and placed on hot plate for several days at 70 °C, or alternatively in an autoclave reaction vessel at around 100°C, for 48 hours.

After above reaction, mixture was cooled down to room temperature and successive washing was carried out using IPA, diethyl ether and toluene. Yellow particles of NiTA were obtained by centrifuge at 2,000 - 6,000 rpm and were dried for further reactions.

In a separate Schott bottle, 5 moles of imidazolium iodide (Iml) were dissolved in IPA, DMSO or H2O and reacted with NiTA product of last reaction. Reaction was carried out at 70°C for another several minutes to hours, alternatively, larger particles as stated above can be reacted in an autoclave vessel at around 100°C for 48 h. Reaction product obtained by either of the above stated methods was allowed to cool down to room temperature and repeated washing was carried out using IPA, diethyl ether and toluene or either of the solvents to achieve final product NiTAIml. This grey product was then stored under nitrogen atmosphere and used to suspend or make colloidal (depending on the solven) in either DMSO, DMF or water to obtain desired conducting coatings.

EXAMPLE 4

In order to study the chemical composition changes upon the reaction of FeTA and FABr, FTIR studies were carried out. A thin film was produced on the ATR crystal and pressed down using swivel press to ensure optimal contact between the sample and crystal using Bruker diamond ATR sampler.

Table 1 presents relative changes in the characteristic FTIR absorption peaks upon the reaction of iron based EMPN (FeTA) with formamidinium bromide (FABr). Characteristic infrared absorption peaks arising in the range of ~ 3300, 1617, 1062 and 670 indicate the integrity of FABr in the metal phenolic network and intercalation of FABr is indicated by relative changes in the hydroxyl, carbonyl and aromatic ring structure absorption frequencies of the EMPN (see Table 1).

Table 1 - IR absorption spectra ofFePN and FePNFABr

Figure 1 shows the corresponding attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectrum of pure tannic acid (solid line) and an electrically conducting EMPN (dashed line).

EXAMPLE 5

The EMPN was synthesises from tannic acid, FeCh and FeCh. The initial product of EMPN was treated with formamidinium bromide to synthesis EMPN. A thin film was produced via spin-coating of the EMPN suspension in DMSO on glass substrate. The film had a thickness of 100+5 nm. Based on this data a sheet resistance of 3488 +/- 101 was calculated, corresponding to a specific conductivity of 28 S/cm.

Moreover, in a separate experiment sheet resistance of 2 K has been observed for fabric coated with an EMPN ink synthesised from Fe and Ti salt, tannic acid and FABr.

Relevant data is reported in Tables 2 and 3.

Figure 2 shows voltage and current read-out of a 4-point probe (1 mm probe spacing) conductivity meter in contact with the obtained EMPN film. Table 2 - Representative examples ofEMPN samples on glass and fabric substrates

Table 3 - Representative examples ofEMPN-composite samples made using various conducing and semi-conducting additives. Samples were spray painted or drop casted on glass substrate and measured using 4-point probe.

EXAMPLE 6

Figure 3 shows the ability of various EMPNs to store electrical charge as active components in electrical charge storage devices. 3a) Cyclovoltammograms of an EMPN (black curve) compared to carbon black (starred curve). 20-25 micron thick solid Ni based EMPN films and carbon films were deposited onto conducting glass for the construction of charge storage devices. In both cases 2.0 mg mass of electroactive active material is used. The electrolyte contained 100 mM LiOH dissolved in a 1: 1 mixture of acetonitrile and valeronitrile. Scan rate: 10 mV/s. The voltage corresponds to the potential applied to the working electrode relative to the potential of a normal hydrogen electrode (NHE).

Figure 3b) Shows the performance of an unsymmetric charge storage device that contains Fe based EMPN as active material on one electrode and Vanadium based EMPN as an active material on the other side of the electrode. The electrical charge storage behaviour of the device is depicted as A/g on the y-axis @ the scan rate of 50 mV/s. 3c) Shows the performance of a planner thin film charge storage device. Such novel electrical charge storage device was fabricated to show case the ability to store electrical charge on extremely thin films of EMPNs. Device was made by spray coating 2 micron thick film of EMPN on an ITO coated glass.

Laser scribing was used to locally remove the EMPN/ITO films and create a set of two electrically isolated finger electrodes pattern, producing a symmetrical interdigitated system each producing a set of 5 interdigitated fingers of EMPN. 10 mm long and 1 mm wide fingers were separated from each other by the laser footprint which was measured to be 20 micron. An all-solid state energy storage device was fabricated by pressing a Nafion membrane onto the interdigitated electrode set to provide a pathway for ionic conductivity between the two fingers of the electrodes. The electrical charge storage behaviour of the device containing 0.22 mg of active EMPN is depicted as A/g on the y-axis @ the scan rate of 50 mV/s. EXAMPLE 7

A sensor device is fabricated to evaluate the performance of EMPN as chemiresistive sensing active layer. A 0.3 pm thick layer of an EMPN was deposited onto an array of interdigitated electrodes with a finger gap of 20 pm. The EMPN was synthesized using iron salts and formamidinium bromide. The thin film was produced via spin-coating of the EMPN suspension in IPA followed by annealing at 150°C. The device was placed in a chamber in ambient conditions and tested under constant potential of 500 mV and a baseline value of resistance arising from the EMPN films was established. Once a constant resistance is established, the device in the chamber was then exposed to an atmosphere with varying amounts of ammonia. The resistance of the film was monitored as a function of time while being exposed to atmospheres with varying amounts of ammonia (see graph, 70-10 ppm = part per million) for about 10 seconds. Figure 4 shows the change in resistance over a period of time for the chemiresistive ammonia sensor using EMPN active sensing layer.

EXAMPLE 8

UV-Vis to NIR spectrum of the EMPN based on iron salts and formamidinium bromide. The thin film of EMPN was produced via spin-coating the EMPN suspension in IPA on a microscopic 2x 2 cm glass slide.

Figure 5 shows the optical absorbance spectrum of a corresponding 0.5 micron thick EMPN film.

EXAMPLE 9

Optical transmittance and sheet resistance data for the EMPN based on iron salts and formamidinium bromide. Thin films were produced via spin-coating of the EMPN suspension on glass slide. Sheet resistances were measured by means of a 4-point probe; optical transmittance was measured by using a spectrophotometer fitted with an integrating sphere.

Figure 6 shows optical transmittances at a wavelength of 550 nm as a function of sheetresistance for the EMPN films, and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) films of various thicknesses. The data points for PEDOT:PSS have been replotted from data published by Seongho Jo et al., Materials Today: Proceedings 10 (2019) 448-455.

EXAMPLE 10

Surface area analysis using physical adsorption of gases for the EMPN synthesised from tannic acid, FeSCU and FeiCSCUh and formamidinium bromide. An EMPN film was produced via blade coating onto a glass plate and subsequent drying. EMPN powder samples were prepared by carefully scratching the powder off the substrate using a sharp blade.

Figure 7 a) and 7b) show differential pore volume as a function of pore width for the EMPN powder sample. This data is derived from the analysis of Brunauer-Emmett-Teller (BET) nitrogen (a) and carbon dioxide (b) adsorption isotherms. The analysis yielded a BET surface area of 104.7 m²/g and 161.5 m²/g for nitrogen and carbon dioxide, respectively.

EXAMPLE 11

Figure 8 shows powder x-ray diffraction (XRD) data of two different EMPN films. Sample (a) was synthesised by the reaction of tannic acid, iron salts (FeSCU and FeiCSCU ) and formamidinium bromide . Sample (b) was synthesised from tannic acid, iron salts (FeCh and FeCh) and formamidinium bromide. Very fine powders of the materials were used on zero background substrate in both cases

EXAMPLE 12

High resolution scanning electron micrograph (SEM) of the EMPN thin film annealed at 150 °C. SEM image shows nano to microporous structure of the EMPN. Intrinsic porosity of such conducting network is highly advantageous especially in applications like chemiresistive sensors.

EXAMPLE 13

The Raman measurements were acquired for the EMPN materials synthesised from tannic acid, iron salts (FeCh and FeCE) and formamidinium bromide (FABr). Relative Raman shift frequencies for the functional groups of FeTA and EMPN are shown in the table below. All major Raman shift frequency peaks corresponding to the formamidinium part also show up in the corresponding EMPN Raman spectra with slight shifts in Raman frequencies, indicating that the overall molecular vibrational modes of FA do not undergo large structural changes after incorporation into the iron polyphenol network. However, cationic association of formamidinium -NH2 closer to Fe centre is observed as a strong Raman shift peak at 602 cm ¹ in the Raman spectra of EMPN as compared to 652 cm ¹ for free -NH2 for pure FABr. Raman spectrum of FABr is also shown for the comparison (see figure 10).

Table 4 - Raman shifts (cm ¹ ) for the functional groups of the FeTA and FeTAFABr (electrically conducting EMPN)

EXAMPLE 14

Ability of the EMPN films to show thermoelectric effect is demonstrated. An EMPN film was deposited onto a glass substrate featuring 2 gold electrodes at a separation of 10 mm. One electrode (cold side) was kept at room temperature while the temperature undernath the second electrode (hot side) was slowly increased locally. EMPN was synthesised from tannic acid, cobalt (II) trifluoromethanesulfonimide and l-Ethyl-3-methylimidazolium iodide. Figure 11 shows thermoelectric voltage response of the corresponding EMPN film.

EXAMPLE 15

Ability of the EMPN coating and films to attenuate various radiofrequency ranges is manifested in this example. In the first instance thin films of Iron and vanadium based EMPNs were spray painted on 7 mm diameter Kapton disks. S21 (forward transmission) values plotted against given radiofrequency range reveal that distinct absorption features can be observed for of the EMPN microwave absorbers having 20+5 micron thickness.. Figure 12 (a) shows forward transmission spectra depicted by S21 parameters of the absorber films (iron and vanadium based EMPN mixed with 5 wt % carbon) measured with PicoVNA vector network analyser connected with an APC-7 connector. In another example, 20 micron thick free-standing EMPN-PMMA films were made with a bulk conductivity of 14 K /sq. 7 mm diameter disks (12.8 mg) were laser cut and tested for EMI shielding efficiency using APC-7 connector attached to the Pico VNA vector network analyser. SET was calculated using the published method (DOI: 10.1039/C4TA04559A) for two frequency ranges in MHz and GHz ranges (12b and 12c)

EXAMPLE 16

X-ray photoelectron spectroscopy (XPS) was used to study elemental composition, chemical and electronic states of various atoms in Fe based EMPN. An EMPN was synthesised from tannic acid, FeCE and FeCh and formamidinium bromide. A thin film was produced via spin-coating of the EMPN suspension in IPA on glass and a subsequent drying process using annealing at 70 °C. 13a provides a survey scan spectrum for the EMPN followed by high resolution scans of the Fe and N peaks (13 b-c), and the Table 5 shows comparative elemental ratio of the elements derived from the survey scan spectrum. Figure 13b shows high resolution Fe2p spectra depicting different oxidation states of iron in the film (Fe(II)/Fe(III) = 3/7). Figure 3c shows high resolution Nls scan, where a typical week 7t-7t* satellite feature several eV from the main peak is observed. Figure 13 a-c XPS spectra were recorded by depositing Fe-EMPN films on an electrically conducting indium-tin oxide (ITO) coated glass substrate.

Table 5 - Elemental ID and Quantification

EXAMPLE 17

Figure 14 (a-c) show XPS spectra of an EMPN film synthesised from tannic acid, TiCE and formamidinium bromide. A thin film was produced via spin-coating of the EMPN suspension in IPA on glass and a subsequent drying process using annealing at 70 °C. Figure 14a provides a survey scan spectrum for the EMPN and the table 6 shows comparative elemental ratio of the elements derived from the survey scan spectrum. Figure 14b shows high resolution Ti2p spectra depicting different oxidation states of titanium in the film (Ti(III)/Ti(IV) = 1.5/8.5). Figure 14c shows high resolution Nls scan, where a typical week satellite feature several eV from the main peak is observed. Figure 14 a-c XPS spectra were recorded by depositing Ti-EMPN films on an electrically conducting indium-tin oxide (ITO) coated glass substrate.

Table 6 - Elemental ID and Quantification EXAMPLE 18

Figure 15 shows capacitive touch sensor device obtained using an EMPN film. A thin film of 1.3 micron of iron based EMPN material dissolved in IPA was spray coated on an interdigitated Au electrode. Additionally, another layer of commercial acrylic paint was applied. Device was attached to a Biologic potentiostat in two electrode geometry and was subjected to a constant applied voltage of 1 V and current was recorded over time. The figure 15 shows changes in current arising from the change in resistance upon the proximity (touched and few cm vicinity) of a human hand (with and without nitrile gloves). Such subtle changes in the resistance arise from local capacitance changes in the EMPN film.

EXAMPLE 19

Figure 16 shows current density (J)-potcntial (V) characteristics of a dye-sensitized solar cell (DSC) fabricated using Fe based EMPN as charge transport material. Double-layer TiC films [2 pm mesoporous TiOi (30 nm) and 2 pm scattering TiOi (400 nm)] sensitized with MK-2 dye were used as light harvesting layer. The electrolyte solution consisting of Fe- EMPN and electrolyte additives was spin coated on the dye- sensitized titania films and was annealed at 70 °C to achieve at 3-4 micron thick charge transport layer. The electrolyte contained 0.20 M EMPN and additives (0.05 M of LiTFSI and 4-trifluromethyl pyridine) dissolved in acetonitrile. Finally, Au counter electrode was evaporated on the EMPN charge extraction layer to complete the circuit. The devices were measured immediately after the device fabrication process.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Glossary:

Fe = Iron

TA = Tannic acid

FeTA = Fe-tannic acid coordination network FAX = Formamidinium halide

GuX = Guanidinium halideFeTAFABr = Fe-tannic acid coordination network reacted with formamidinium bromide salt

EMPN = Electrically conducting metal polyphenolic network

Claims

, , , , , , , , , , , , , , , , Cr²⁺, MO²⁺, W²⁺, Mn²⁺, Re²⁺, Li¹⁺, Cs¹⁺,Os²⁺, Co²⁺, Rh²⁺, Ir²⁺, Ni²⁺, Pd²⁺, Pt²⁺, Cu²⁺, Ag²⁺, AU²⁺, Zn²⁺, Cd²⁺, B²⁺, Al²⁺, Ga²⁺, Si²⁺, Sn²⁺, Pb²⁺, Hg²⁺, As²⁺, Te²⁺, La²⁺, Ce²⁺, Pr²⁺. Sm²⁺, Gd²⁺, Nd²⁺, Db²⁺, Tb²⁺, Tm²⁺, and Yb²⁺.

5. The EMPN of any one of claims 1-4, wherein the metal cations are cations of the same metal element.

6. The EMPN of any one of claims 1-5, wherein the counter-ion is selected from a metal counter-ion, an organic counter-ion, and a combination thereof.

7. The EMPN of claim 6, wherein the organic counter-ion is a fluorinated ionic polymer, a fluorinated non-ionic polymer, a polyol, or a polyacrylic.

8. The EMPN of claim 6, wherein the organic counter-ion is selected from formamidinium, guanidinium, ethidium, tetrabutylammonium, imidazolium, polyethyleneimine, polyallylamine, polylysine, and polyvinylimidazolium poly [(1- vinyl-3 - ethy limidazolium) .

9. The EMPN of any one of claims 1-6, wherein the organic counter-ion is a polycation.

10. The EMPN of any one of claims 1-9, wherein the polyphenol is selected from a synthetic or plant polyphenolic material, tannins, tannic acid, gallic acid, a catechin, a flavonoid, a chaicone, a procyanidin, and an anthocyanidin.

11. The EMPN of any one of claims 1-10, presenting as a solid.

12. The EMPN of claim 11, being provided in the form of a film, gel, or powder.

13. The EMPN of any one of claims 1-12, further comprising a conductor or semiconductor material.

14. A composite comprising an electrically conducting metal phenolic network (EMPN) according to any one of claims 1-13, wherein the EMPN is mixed or layered with a topcoat.

15. The composite of claim 14, wherein the topcoat comprises polyacrylic or polyurethane.

16. Use of an electrically conducting metal phenolic network (EMPN) according to any one of claims 1-13, or of a composite of claim 14 or 15 in or in the provision of:

(i) an electrically conductive or semi-conductive paint or ink on a substrate,

(ii) an electromagnetic interference shield or radar absorbing material,

(iii) an electrode for catalysis for electrochemical conversion,

(iv) an electrode for electrochemical or photoelectrochemical sensing in liquid or airborne media,

(v) a thermoelectric device, or

(vi) a touch sensitive surface.

17. A method of making an electrically conducting metal phenolic network (EMPN) according to any one of claims 1-13, the method comprising the steps of: a) combining at least one metal cation source and the polyphenol in a solution, wherein the polyphenol is deprotonated to obtain a cation/polyphenol coordination compound, the cation/polyphenol coordination compound comprising the one or more metal cations, and b) combining the cation/polyphenol compound with a counter-ion salt in a solution to obtain the EMPN.

18. The method of claim 17, wherein the process further comprises step c) of adding an organic conductor or semi-conductor to the EMPN.

19. The method of claim 17 or 18, wherein one metal cation source is used in step a), and the metal cation derives from that metal cation source.

20. The method of any one of claims 17-19, wherein step a) and/or step b) comprise(s) heating the solution to a temperature of at least 25 °C.

21. The method of any one of claims 17-20, wherein the at least one metal cation source comprises a chloride anion, a bromide anion, a sulphide anion, a iodide anion, or a hydroxide anion.

22. The method of any one of claims 17-20, wherein the at least one metal cation source comprises a nitrate salt, a sulphate salt, an acetate salt, a formate salt, a propionate salt, a borate salt, a haloborate salt, a cyanoborate salt, a trifluoromethanesulfonate salt, a trifluoromethanesulfonimide salt, a phosphate salt, or a halophosphate salt.

23. The method of any one of claims 17-22, wherein the at least one metal cation source comprises a metal cation selected from one or more of Fe⁶⁺, Fe⁴⁺, Fe³⁺, Fe²⁺, Fe⁺, Cu⁴⁺, Cu³⁺, Cu²⁺, Cu⁺, Li⁺, Rb⁺, Cs⁺, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Sc³⁺, Sc²⁺, Sc⁺, Y³⁺, Y²⁺, Y⁺, Ti⁴⁺, Ti³⁺, Ti²⁺, Zr⁴⁺, Zr³⁺, Zr²⁺, Hf⁴⁺, Hf³⁺, V⁵⁺, V⁴⁺, V³⁺, V²⁺, Nb⁵⁺, Nb⁴⁺, Nb³⁺, Nb²⁺, Ta⁵⁺, Ta⁴⁺, Ta³⁺, Ta²⁺, Cr⁶⁺, Cr⁵⁺, Cr⁴⁺, Cr³⁺, Cr²⁺, Cr⁺, Cr, Mo⁶⁺, Mo⁵⁺, Mo⁴⁺, Mo³⁺, Mo²⁺, Mo⁺, Mo, W⁶⁺, W⁵⁺, W⁴⁺, W³⁺, W²⁺, W⁺, Mn⁷⁺, Mn⁶⁺, Mn⁵⁺, Mn⁴⁺, Mn³⁺, Mn²⁺, Mn⁺, Re⁷⁺, Re⁶⁺, Re⁵⁺, Re⁴⁺, Re³⁺, Re²⁺, Re⁺, Ru⁸⁺, Ru⁷⁺, Ru⁶⁺, Ru⁴⁺, Ru³⁺, Ru²⁺, Os⁸⁺, Os⁷⁺, Os⁶⁺, Os⁵⁺, Os⁴⁺, Os³⁺, Os²⁺, Os⁺, Os, Co⁵⁺, Co⁴⁺, Co³⁺, Co²⁺, Co⁺, Rh⁶⁺, Rh⁵⁺, Rh⁴⁺, Rh³⁺, Rh²⁺, Rh⁺, Ir⁶⁺, Ir⁵⁺, Ir⁴⁺, Ir³⁺, Ir²⁺, Ir⁺, Ir, Ni³⁺, Ni²⁺, Ni⁺, Ni, Pd⁶⁺, Pd⁴⁺, Pd²⁺, Pd⁺, Pd, Pt⁶⁺, Pt⁵⁺, Pt⁴⁺, Pt³⁺, Pt²⁺, Pt⁺, Ag³⁺, Ag²⁺, Ag⁺, AU⁵⁺, AU⁴⁺, AU³⁺, AU²⁺, AU⁺, Zn²⁺, Zn⁺, Zn, Cd²⁺, Cd⁺, Hg⁴⁺, Hg²⁺, Hg⁺, B³⁺, B²⁺, B⁺, Al³⁺, Al²⁺, Al⁺, Ga³⁺, Ga²⁺, Ga⁺, In³⁺, In²⁺, In¹⁺, Tl³⁺, Tl⁺, Si⁴⁺, Si³⁺, Si²⁺, Si⁺, Ge⁴⁺, Ge³⁺, Ge²⁺, Ge⁺, Ge, Sn⁴⁺, Sn²⁺, Pb⁴⁺, Pb²⁺, As⁵⁺, As³⁺, As²⁺, As⁺, Sb⁵⁺, Sb³⁺, Bi⁵⁺, Bi³⁺, Te⁶⁺, Te⁵⁺, Te⁴⁺, Te²⁺, La³⁺, La²⁺, Ce⁴⁺, Ce³⁺, Ce²⁺, Pr⁴⁺, Pr³⁺, Pr²⁺, Nd³⁺, Nd²⁺, Sm³⁺, Sm²⁺, EU³⁺, EU²⁺, Gd³⁺, Gd²⁺, Gd⁺, Tb⁴⁺, Tb³⁺, Tb²⁺, Tb⁺, Db³⁺, Db²⁺, Ho³⁺, Er³⁺, Tm⁴⁺, Tm³⁺, Tm²⁺, Yb³⁺, Yb²⁺, and Lu³⁺.

24. The method of any one of claims 17-23, wherein the counter-ion salt is selected from formamidinium, guanidinium, ethidium, tetrabutylammonium, imidazolium, polyethyleneimine, polyallylamine, polylysine, polyvinylimidazolium poly [(1- vinyl-3 - ethylimidazolium), a fluorinated ionic and non-ionic polymer, a polyol, and a polyacrylic.

25. The method of any of the claims 17-24, wherein the EMPN is at least partially reacted with an electrically non-conducting polymer powder or film to form a conductive freestanding film, coating, or curable resin.