RU2762313C1 - Electrode material made of manganese oxide with a birnessite or vernadite structure and method for production thereof - Google Patents

Abstract

FIELD: electrodes.

SUBSTANCE: invention relates to the technology of electrochemical production, namely, to development of a method for producing electrode materials from manganese oxide with a birnessite or vernadite structure for use in supercapacitors, electrochromic apparatuses, batteries, accumulators, fuel elements. The method for producing electrode materials from oxide with birnessite or vernadite structures by means of cathodic reduction of permanganate or manganate in an alkaline medium consists in conducting cathodic polarisation of a conductive substrate in solutions of alkali metal hydroxides with permanganate additives. Deposition is realised in potentiostatic conditions in a three-electrode electrochemical cell.

EFFECT: high mechanical and adhesive stability in operation in apparatuses with an alkaline electrolyte, stability and quickness of cycling, ease of production and high capacity.

11 cl, 4 dwg, 12 ex, 1 tbl

Description

Technology area

The invention relates to the technology of electrochemical production, namely to the development of a method for producing electrode materials from manganese oxide with the structure of birnessite or vernadite by cathodic reduction of permanganate or manganate in an aqueous alkaline medium for use in supercapacitors, electrochromic devices, batteries, accumulators, fuel cells.

State of the art

Electrochemical power engineering is currently actively developing both in terms of autonomous power supply (electric vehicles, aircraft, water transport, etc.), and as an important element of energy systems (energy storage, load regulation in power grids). The main direction for further increasing the efficiency of electrochemical storage and conversion of energy is the creation of electrode materials, the advantages of which over the used analogs are in improved functional characteristics (higher capacity, higher catalytic activity, lower resistance), and / or lower cost, and / or higher stability.

The question of stability is directly related to the economic aspects of designing electrochemical devices, since higher stability allows longer service life and less frequent replacement of electrode material. The best guarantee of high stability of a solid electrode material is its thermodynamic stability in an electrolyte solution at the potentials at which the electrode functions. Metals, with the exception of noble ones, never satisfy the condition of thermodynamic stability. The abandonment of precious metals is stimulated by the goal of reducing the cost of devices. In this regard, the search for stable oxides of base metals is urgent. For this group of electrode materials, the most severe limitation is sufficient electronic conductivity.

Manganese oxides occupy a special place among oxide electrode materials precisely because of the high conductivity required to reduce ohmic losses in electrochemical devices. Manganese oxides are the general name for a large group of materials with different crystal structures and different Mn: O ratios. In some cases, they also contain singly charged A cations (alkali metal ions or protons). The composition of manganese oxides can generally be represented as A _x MnO ₂ . Like most other base metal oxides, manganese oxides can only function in devices with alkaline or much less commonly used neutral electrolytes. Birnessite and vernadite are thermodynamically stable modifications of manganese oxide in an alkaline medium - layered phases in which A are sodium or potassium cations, x is 0.01-0.45, which corresponds to the oxidation states of manganese 3.99-3.55.

The most widely used in commercial batteries and accumulators with an alkaline electrolyte is electrolytic manganese dioxide (EDM), obtained from divalent manganese salts by an anodic oxidation process using a detailed industrial technology [Avijit Biswal, Bankim Chandra Tripathy, Kali Sanjay, Tondepu Subbaiah and Manickam Minakshi, " Electrolytic manganese dioxide (EMD): a perspective on worldwide production, reserves and its role in electrochemistry ", RSC Advances, 2015, v. 5, no.58255]. We do not consider EDM as an analogue because it does not contain birnessite or vernadite that are stable in an alkaline solution, and gradually transforms during operation in alkaline devices. The reason is that EDM is formed in acidic solutions, its composition is close to MnO ₂ , and the predominant crystalline phase is gamma-MnO ₂ . It is impossible to carry out the process of precipitation of EDM in an alkaline medium because its precursors, divalent manganese compounds, are insoluble in an alkaline medium. At the same time, the functional characteristics of EDM are "reference" for any oxides used in charge-storage devices.

There are two technologies for producing birnessite or vernadite.

From the prior art, electrode materials with a birnessite or vernadite structure are known, obtained by chemical reduction reactions [CN 105502504] or oxidation [US 20180134576]. However, these materials are obtained in the form of powders, and for the manufacture of electrodes from them additional technological steps are required: creating a composition with some binder, suspending such a pomp, applying the resulting suspension to a substrate, and drying. Along with the technological complexity, there is also the risk of low adhesion to the substrate, because lagging behind is the strong binding of the powder particles to the substrate.

, T.M. Silva, M.J. Carmezim, M.F. Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039/c7ra04481j; S. Zhu, W. Huo, X. Liu, Y. Zhang, Birnessite based nanostructures for supercapacitors: challenges, strategies and prospects, Nanoscale Adv. 2 (2020) 37-54. doi: 10.1039/c9na00547a] или при концентрации щелочи на два порядка ниже, чем в рабочих растворах устройств (рН 12) [Н. Yuqiu, Z. Hongcheng, Cathodic Potentiostatic Electrodeposition and Capacitance Characterization of Manganese Dioxide Film, in: 2010 International Conference on Nanotechnology and Biosensors IPCBEE, Vol. 2, IACSIT Press, Singapore, 2011, pp. 130-133]. Однако при переносе в раствор с более высокой концентрацией щелочи (рН > 14, высокие концентрации щелочи необходимы для обеспечения достаточной электропроводности раствора) эти материалы неизбежно претерпевают структурные трансформации, связанные с изменением их катионного состава. Такие трансформации следует рассматривать как деградационный риск. Кроме того, в разработках не уделяется внимания равномерности нанесения оксида на подложку, т.к. осаждение проводится в ячейках, не обеспечивающих равномерного распределения линий тока.From the prior art, electrode materials with a birnessite or vernadite structure are known, obtained by cathodic reduction of permanganate or manganate in a neutral environment [T. Tanimoto, H. Abe, K. Tomono, M. Nakayama, Cathodic Synthesis of Birnessite Films for Pseudocapacitor Application, ECS Trans. 50 (2013) 61-70. doi: 10.1149 / 05043.0061ecst; R. Delia Noce,

, TM Silva, MJ Carmezim, MF Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO ₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039 / c7ra04481j; S. Zhu, W. Huo, X. Liu, Y. Zhang, Birnessite based nanostructures for supercapacitors: challenges, strategies and prospects, Nanoscale Adv. 2 (2020) 37-54. doi: 10.1039 / c9na00547a] or at an alkali concentration two orders of magnitude lower than in working solutions of devices (pH 12) [N. Yuqiu, Z. Hongcheng, Cathodic Potentiostatic Electrodeposition and Capacitance Characterization of Manganese Dioxide Film, in: 2010 International Conference on Nanotechnology and Biosensors IPCBEE, Vol. 2, IACSIT Press, Singapore, 2011, pp. 130-133]. However, when transferred to a solution with a higher alkali concentration (pH> 14, high alkali concentrations are necessary to ensure sufficient electrical conductivity of the solution), these materials inevitably undergo structural transformations associated with a change in their cationic composition. Such transformations should be considered as a degradation risk. In addition, the development does not pay attention to the uniformity of the oxide deposition on the substrate, because deposition is carried out in cells that do not provide a uniform distribution of streamlines.

, T.M. Silva, M.J. Carmezim, M.F. Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039/c7ra04481j). Способ заключается в осаждении перманганата или манганата на нержавеющую сталь AISI 304 из нетрального (рН 7) раствора 10 мМ KMnO₄ с добавкой 0.1 М Na₂SO₄ в малоконтролируемых гальваностатических режимах (без контроля потенциала). Выходы по току составляли от 20 до 96%. Однако, бирнессит был рентгенографически идентифицирован только при не слишком высоких плотностях тока, при этом достигались емкости 170-250 Ф/г при медленном перезаряжении и 75-150 Ф/г при быстром перезаряжении. Данных по изменению емкости при циклировании для рентгенографически идентифицированных образцов не приводится.Known electrode material with the structure of birnessite or vernadite, obtained by cathodic reduction of permanganate or manganate in a neutral environment (R. Delia Noce,

, TM Silva, MJ Carmezim, MF Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO ₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039 / c7ra04481j). The method consists in the deposition of permanganate or manganate on stainless steel AISI 304 from a neutral (pH 7) solution of 10 mM KMnO ₄ with the addition of 0.1 M Na ₂ SO ₄ in poorly controlled galvanostatic modes (without potential control). The current efficiency ranged from 20 to 96%. However, birnessite was identified by X-ray only at not too high current densities, while capacities of 170-250 F / g were achieved at slow recharge and 75-150 F / g at fast recharge. Data on the change in capacity during cycling for X-ray identified samples are not provided.

The technology for producing electrode materials by cathodic reduction of permanganate or manganate on a substrate provides a material in one stage, in which the growth of an oxide with a layered structure (birnessite or vernadite) occurs from crystalline nuclei firmly bound to the substrate surface. The resulting material does not undergo further structural transformations when operating in alkaline solutions, since, unlike analogs, it is formed directly in an alkaline medium. Thus, degradation risks associated with mechanical destruction of the material layer are reduced. At the same time, the functional characteristics remain comparable or superior to those typical for materials based on manganese oxides obtained in other ways.

The closest to the claimed material is an electrode material with the structure of birnessite or vernadite, obtained by potentiostatic deposition from permanganate or manganate on platinum foil from neutral (pH 6.5) solutions of 2 mM KMnO ₄ with the addition of 0 0.5 M of various chloride salts. The deposition potentials were from -0.1 to +0.25 V on the silver chloride electrode scale. The current efficiency was 94%. Capacities of up to 320 F / g were achieved with a slow (1 mV / s) recharge, with the transition to faster charging (200 mV / s) the capacities decreased to 200 F / g. The reduction in capacity over 1000 cycles was about 15%. However, the above characteristics are not too high from the point of view of the competitiveness of capacitors with birnessite electrodes with conventional carbon supercapacitors, primarily in terms of the loss of capacity with an increase in the recharge rate and during cycling. In addition, all data on capacity were obtained in neutral solutions, which (unlike alkaline solutions) do not provide stable operation of electrochemical devices due to the instability of the pH value in the near-electrode layer. When transferred to an alkaline solution, films obtained from neutral solutions crack.

The technical problem to be solved by the claimed invention is to obtain an electrode material with a birnessite or vernadite structure directly in the same environment, in which the material is then used as a functional one.

Disclosure of invention

The technical result of the claimed invention is the creation of a rechargeable electrode material for capacitors, characterized by high mechanical and adhesive stability when operating in devices with an alkaline electrolyte. The inventive electrode material is also characterized by stability and speed of cycling, ease of production and high capacity (up to 500 F / g). The sediment, firmly bound to the surface of the substrate, does not change the mass within the achievable accuracy of its determination after 1000 complete cycles. According to electron microscopy data, including microscopy on cross sections and chips, as well as according to diffraction data, the deposit is characterized by uniformity in thickness and composition, which is achieved by the uniform distribution of potential and streamlines along the surface during deposition. The loss of capacity after 1000 full cycles does not exceed 10%. The decrease in capacity while reducing the recharge time from a few minutes to a few seconds does not exceed 20%.

The technical result is achieved by an electrode material made of manganese oxide with a crystal structure of birnessite or vernadite for the manufacture of electrodes for electrochemical devices with an aqueous alkaline electrolyte, characterized by a uniform microstructure with an oxide loading of up to 1.6 mg per cm ² and a capacity of up to 500 F / g, preferably from 200 to 500 F / g. At a material recharge rate of 200 mV / s, the capacity is reduced by no more than 20%, preferably no more than 15%. The conductive substrate is made of carbon, nickel, or steel.

The technical result is also achieved by a method of producing an electrode material from manganese oxide with a crystal structure of birnessite or vernadite, including preparing a solution (electrolytic medium, electrolyte) by mixing an aqueous alkaline solution and an aqueous solution of permanganate. The resulting solution is placed in a three-electrode electrochemical cell, including a working electrode, which is used as a conductive substrate for the deposition of electrode material, an auxiliary electrode and an oxide-mercury reference electrode. The resulting solution is deaerated with an argon current for the time required to remove oxygen, then the potential of the working electrode is set from -0.05 to -0.25 V by the oxide-mercury electrode in an alkali solution of the same concentration, deposition is carried out until the specific missed charges are reached 0.039 4 C / cm ² based on the geometric surface of the substrate, then the substrate with the electrode material is repeatedly washed to remove contamination and unreacted residues of manganese salts. The conductive substrate is a carbon, nickel, or steel substrate. To prepare an alkaline solution, use KOH or NaOH or LiOH, while the concentration of alkali in the solution is from 1 to 5 mol / L. Potassium permanganate KMnO ₄ or sodium permanganate NaMnO _{4 is} used as permanganate, while the concentration of permanganate in the solution is from 1 to 20 mmol / L. To wash the oxide on the substrate, a background alkaline electrolyte is used, taken in a volume not less than 100 times the volume of the obtained deposited layer. Prior to placement in the cell, the conductive substrate is subjected to an oxidative chemical treatment. The time for deaeration with argon flow is at least 30 minutes, preferably from 30 to 90 minutes.

Brief Description of Drawings

FIG. 1 shows the design of an electrochemical cell for cathodic deposition, where 1 base, 2 working electrode holder, 3 working electrode stopper, 4 leg, 5 leg base, 6 water chamber, 7 water chamber cover, 8 - working electrode chamber, 9 - auxiliary electrode holder ...

FIG. 2 shows the X-ray diffraction patterns of oxides obtained at deposition potentials -0.25 and -0.05 V. Cu Kalfa radiation.

, T.M. Silva, M.J. Carmezim, M.F. Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039/c7ra04481j] (1) и полученных в рамках настоящего изобретения из щелочного раствора перманганата при при потенциалах осаждения -0.25 и -0.05 В (2), где (а) - при потенциале осаждения -0.25 В, (b) - при потенциале осаждения -0.05 В.FIG. 3 compares electron microscopic images of sediments obtained from a neutral solution of permanganate in [R. Delia Noce,

, TM Silva, MJ Carmezim, MF Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO ₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039 / c7ra04481j] (1) and obtained within the framework of the present invention from an alkaline solution of permanganate at a deposition potential of -0.25 and -0.05 V (2), where (a) - at a deposition potential of -0.25 V, (b) - at deposition potential -0.05 V.

FIG. 4 shows the graphs of the specific capacity depending on the sweep speed for birnessite, cathode deposited from a neutral solution of 0.5M Na ₂ SO ₄ (c), from [T. Tanimoto, H. Abe, K. Tomono, M. Nakayama, Cathodic Synthesis of Birnessite Films for Pseudocapacitor Application, ECS Trans. 50 (2013) 61-70] and specific capacity, depending on the potential scan rate, for a deposit obtained at -0.25 V on a nickel substrate in an alkaline electrolyte (d).

Implementation of the invention

The method of producing electrode materials from oxide with birnessite or vernadite structures by cathodic reduction of permanganate or manganate in an alkaline medium consists in carrying out cathodic polarization of a conducting substrate in solutions of alkali metal hydroxides with addition of permanganate. When stored in air, permanganate is gradually spontaneously reduced by water to manganate, which does not cause complications during the further process. A substrate of carbon, nickel or steel with a diameter of 15 ± 0.5 mm and a thickness of 0.5-5 mm is degreased by any standard method, for example, in acetone, and subjected to an oxidative chemical treatment and introduced as a working electrode into a solution in an electrochemical cell of an original design (Fig. one). The cell also contains an auxiliary electrode and a reference electrode, relative to which the required deposition potential is set using a potentiostat. The geometry of the cell allows for the uniformity of the deposited layer both in thickness and in composition, depending on the potential. The proposed geometry provides a uniform distribution along the surface of both the potential and streamlines during deposition.

The three-electrode deposition cell (FIG. 1) is of a cylindrical type. The main part in contact with the solution is made of Teflon (working electrode chamber, water chamber, water chamber cover, auxiliary electrode holder, working electrode holder). The working electrode is a substrate on which the deposition is carried out (the height is determined by the material, ∅ _external = 15 mm). The auxiliary electrode is made of steel (rod, ∅ = 15 mm), the reference electrode is an oxide-mercury one in a glass case (not shown). The working electrode chamber is a cylinder (h = 60 mm, ∅ _internal = 41 mm, ∅ _external = 58 mm) with internal and external threads, by means of which the working chamber, holders of the working and auxiliary electrodes, and also the water chamber are connected. The working electrode holder is a cylinder (h = 25 mm, ∅ _external = 41 mm) with a stepped hole (h ₁ = 20 mm, ∅ _{internal 1} = 15 mm, h ₂ = 5 mm, ∅ _{internal 2} = 11 mm) and external and internal threads. Using an external thread, the working electrode holder is screwed to the working chamber. A working electrode is placed in a hole with an internal thread and is fixed with a stopper of the working electrode made of caprolon in the form of a washer with internal and external threads (h = 5 mm, ∅ _external = 17 mm). With the help of an external thread, the stopper fixes the working electrode in the holder, and with the help of the internal thread, the current collector is fixed in it (steel stud M5). The auxiliary electrode holder is made in the form of a washer (h = 10 mm, ∅ _external = 41 mm) with an external thread and holes for fixing the auxiliary electrode (∅ = 15 mm) and deaeration (∅ = 3 mm). The auxiliary electrode holder is connected to the working chamber by means of a threaded connection. The water chamber consists of two parts: a chamber made in the form of a cylinder (h = 50 mm, ∅ _inside = 67 mm, 0 outside = 79 mm) with a stepped hole (h ₁ = 44 mm, ∅ _{inside 1} = 67 mm, h ₂ = 6 mm, ∅ _{internal 2} = 57 mm), internal thread and holes for water supply (2 holes M8) and a cover made in the form of a washer (h = 17 mm, ∅ _internal = 57 mm, ∅ _external = 79 mm) with internal thread. Parts of the water chamber are connected to the working chamber using threaded connections. The assembled main part of the cell is installed on a pedestal consisting of a base and legs with bases of legs. The base is made in the form of a plexiglass parallelepiped with a stepped hole (h ₁ = 5 mm, ∅ _{inner 1} = 80 mm, h ₂ = 10 mm, ∅ _{inner 2} = 40 mm) for installing the main part and threaded holes (M8) for fixing the legs. The legs and bases of the legs are made of duralumin and represent rods h = 100 mm, ∅ _external = 8 mm and h = 15 mm, ∅ _external = 20 mm, respectively, with M8 thread. The legs are connected to the base and the base of the leg by means of a threaded connection.

The deposition can also be carried out in three-electrode cells of other designs, however, in this case, deposits can be obtained uneven in thickness and in stoichiometric composition (i.e., in the oxidation state of manganese). To monitor the deposition process, the dependences of the flowing current and the passed charge on time are recorded at a fixed potential. From the amount of the passed charge, using the known current efficiency, the specific amount of the deposited oxide per unit surface of the substrate is calculated.

To obtain the electrode material, the starting compounds are (1) alkali (KOH, or NaOH or LiOH) and (2) potassium permanganate KMnO ₄ . An aqueous solution is prepared from (1) and (2), preferably with constant stirring. The concentration of alkali in solution is from 1 to 5 mol / l, permanganate or manganate from 1 to 20 mmol / l. The resulting solution is placed in a cell (Fig. 1) and deaerated with an argon flow for at least 30 minutes. The deaeration time can be arbitrarily increased and does not affect the result. Then, the potential of the working electrode is set from -0.05 to -0.25 V by the oxide-mercury electrode in an alkali solution of the same concentration (below, all the values of the potential are given on the scale of this reference electrode). During deposition, the current and the transmitted charge are recorded. The deposition is carried out until the specific missed charges reach 0.039-4 C / cm ² calculated on the geometric surface of the substrate, which corresponds to the amount of oxide in the film (load) 0.013 1.6 mg / cm ² . The lower limit of this interval corresponds to the loads actual for the cathode of the fuel cell, the upper limit to the loads for use in electrochemical capacitors. Next, the resulting oxide on the substrate is washed to remove impurities and unreacted permanganate residues with a background electrolyte solution, in an amount not less than 100 times the volume of the resulting deposited layer (precipitate). When using substrates made of metals and oxidized carbon, the current efficiency is at least 90%.

The present invention is illustrated by specific examples of execution, which are not the only possible, but clearly demonstrates the possibility of achieving the required technical result.

Example 1.

A glassy carbon disk 2 mm thick and 15 mm in diameter was used as a working electrode in the cell (Fig. 1). Before deposition, the electrode was polarized for 10 s at 1.8 V using a mercury oxide electrode in a NaOH solution with a concentration of 1 mol / L. Then 1.0 g of NaOH was dissolved in 24 ml of H ₂ O, obtaining a solution with a concentration of 1 mol / L. To this solution was added 0.078 g of potassium permanganate KMnO ₄ , obtaining a solution with a permanganate concentration of 20 mmol / L. The resulting solution was placed in a cell and deaerated with an argon flow for 30 min. Then the potential of the working electrode was set at -0.25 V over the mercury oxide electrode in an alkali solution of the same concentration. During deposition, the current and the transmitted charge were recorded. The deposition was carried out until the specific charge reached 1.06 C / cm ² , which corresponds to the amount of oxide in the film (load) of 0.39 mg / cm ² . The resulting oxide on the substrate was removed from the cell, kept for 3 times for 20 minutes in 30 ml of distilled water with slight stirring, and dried at room temperature. Thereafter, the crystal structure of the oxide was confirmed by X-ray diffraction. The results are shown in FIG. 2. The X-ray diffraction pattern of the sample corresponds to the structure of birnessite, which is characterized by layering and high disordering, which leads to a significant broadening of reflections. The resulting precipitate consists of thin lamellae forming characteristic globules with high porosity, as shown in FIG. 3 (right, a). This morphology is typical for birnessite. Thus, in the course of the experiment, the declared phase was actually obtained.

Example 2.

Carried out analogously to example 1, but during deposition set the potential of the working electrode -0.05 V for mercury oxide electrode in an alkali solution of the same concentration. The deposition was carried out until the specific charge reached 1.06 C / cm ² , which corresponds to the amount of oxide in the film (load) of 0.30 mg / cm ² . The crystal structure of the oxide was confirmed by X-ray diffraction. The results are shown in FIG. 2. The X-ray diffraction pattern of the obtained sample is characterized by a set of reflections close to the X-ray diffraction pattern of birnessite. However, it lacks the first two reflections, which indicates the absence of interlayer ordering, which is characteristic of the vernadite structure. The resulting sediment has a compact morphology and is permeated with nanosized pores (Fig. 3 on the right, b). A much denser structure in comparison with highly branched birnessite provides a significantly higher mechanical stability of the resulting sediment.

Example 3.

Carried out similarly to that described in example 2, but immediately after deposition, the substrate with the resulting oxide was washed with 30 ml of a background alkaline electrolyte solution for 3 minutes. After that, the electrode was again placed in the cell and filled with 25 ml of a solution of the background alkaline electrolyte. The solution was deaerated with an argon flow for 30 min. Then, the electrode was subjected to cyclic application of potential in the range from –0.03 to 0.27 in the mode with a linear potential scan at a rate of 0.1 V / s. During the experiment, 1000 complete cycles were carried out, a decrease in capacity of about 10% was observed after 1000 cycles. During the cycling the amount of the oxide on the substrate is not changed (up to weight the error determination for materials extracted from the solution and subjected to drying): it was 0.30-0.32 mg / cm ^2. Thus, during the cycling of the potential, the sludge does not lose its mechanical stability.

Example 4.

, T.M. Silva, M.J. Carmezim, M.F. Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039/c7ra04481j], высокая обратимость перезаряжения пленки бирнессита, полученного в щелочной среде, сохраняется до гораздо более высоких значений скоростей развертки потенциала.A disc made of sheet nickel 0.5 mm thick and 15 mm in diameter was used as a working electrode in the cell (Fig. 1). Before deposition, the electrode was subjected to polarization for 100 s at -1.1 V using a mercury oxide electrode in a NaOH solution with a concentration of 1 mol / L. Then 1.0 g of NaOH was dissolved in 24 ml of H ₂ O, obtaining a solution with a concentration of 1 mol / L. To this solution was added 0.078 g of potassium permanganate KMnO ₄ , obtaining a solution with a permanganate concentration of 20 mmol / L. The resulting solution was placed in a cell and deaerated with an argon flow for 30 min. Then the potential of the working electrode was set at -0.25 V over the mercury oxide electrode in an alkali solution of the same concentration. During deposition, the current and the transmitted charge were recorded. The deposition was carried out until the specific charge reached 0.039 C / cm ² , which corresponds to the amount of oxide in the film (load) of 0.013 mg / cm ² . After deposition, the substrate with the resulting oxide was washed with 30 ml of the background alkaline electrolyte solution for 3 minutes. After that, the electrode was again placed in the cell and filled with 25 ml of a solution of the background alkaline electrolyte. The solution was deaerated with an argon flow for 40 min. Then, the electrode was subjected to cyclic application of potential in the range from –0.15 to 0.27 in the mode with a linear potential sweep with various sweep rates in the range of 1–2000 mV / s. The obtained dependences of the specific capacity on the charging rate are presented in Fig. 4. Comparing the results obtained with those described in T. Tanimoto, H. Abe, K. Tomono, M. Nakayama, Cathodic Synthesis of Birnessite Films for Pseudocapacitor Application, ECS Trans. 50 (2013) 61-70 for the range up to 200 mV / s, it can be noted that the precipitate obtained in an alkaline solution demonstrates a significantly higher specific capacity of 500 F / g, which at 200 mV / s decreases to 420 F / g. At an order of magnitude even faster recharge of 2000 mV / g, the capacity remains above 200 F / g. As follows from a comparison of voltammograms for the resulting sediment and precipitation from [R. Delia Noce,

, TM Silva, MJ Carmezim, MF Montemor, Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO ₂ electrochemical capacitor electrodes, RSC Adv. 7 (2017) 32038-32043. doi: 10.1039 / c7ra04481j], the high recharge recharge of the byrnessite film obtained in an alkaline medium is retained up to much higher potential sweep rates.

Examples 5-12 were carried out analogously to example 1, the parameters are shown in the table.

Claims (11)

1. A method of producing an electrode material from manganese oxide with a crystal structure of birnessite or vernadite, including preparing an electrolyte by mixing an aqueous alkaline solution and a permanganate solution, the resulting solution is placed in a cell including a working electrode, which is used as a conductive substrate for deposition of electrode material, an auxiliary electrode and oxide-mercury reference electrode, the electrolyte is deaerated with an argon current for the time required to remove oxygen, then the potential of the working electrode is set from -0.05 to -0.25 V over the oxide-mercury electrode in an alkali solution of the same concentration, deposition is carried out until the specific missed charges 0.039 - 4 C / cm ² calculated on the geometric surface of the substrate, then the substrate with the electrode material is repeatedly washed to remove contamination and unreacted residues of manganese salts. 2. A method according to claim 1, characterized in that a carbon, nickel or steel substrate is used as the conductive substrate. 3. The method according to claim 1, characterized in that KOH, or NaOH, or LiOH is used to prepare the alkaline solution. 4. The method according to claim 3, characterized in that the concentration of alkali in the solution is from 1 to 5 mol / l. 5. The method according to claim 1, characterized in that potassium permanganate KMnO ₄ or sodium permanganate NaMnO _{4 is} used as the permanganate, 6. The method according to claim 5, characterized in that the concentration of permanganate is from 1 to 20 mmol / l. 7. The method according to claim 1, characterized in that for washing the oxide on the substrate, a background alkaline electrolyte is used, taken in a volume not less than 100 times the volume of the obtained deposited layer. 8. The method according to claim 1, characterized in that the pre-conductive substrate is subjected to an oxidative chemical treatment. 9. Electrode material of manganese oxide with a crystal structure of birnessite or vernadite for the manufacture of electrodes for electrochemical devices with an aqueous alkaline electrolyte, obtained by the method according to claim 1, characterized by a uniform microstructure with the amount of oxide in the film up to 1.6 mg / cm ² and a capacity of up to 500 F /G. 10. The electrode material of claim 9, wherein the material has a capacity of 200 to 500 F / g. 11. Electrode material according to claim 9, characterized in that at a material recharge rate of 200 mV / s, the capacitance decreases by no more than 20%.

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