WO2021209831A1

WO2021209831A1 - A hybrid transparent conducting electrode and method thereof

Info

Publication number: WO2021209831A1
Application number: PCT/IB2021/052083
Authority: WO
Inventors: Giridhar Udapi KULKARNI; Indrajit MONDAL; Ashutosh Kumar Singh
Original assignee: Centre For Nano And Soft Matter Sciences
Priority date: 2020-04-18
Filing date: 2021-03-12
Publication date: 2021-10-21

Abstract

The invention is related to a method for fabrication of hybrid transparent conducting electrodes comprising Aluminium mesh, Tin(IV)oxide. The method facilitates the fabrication of transparent electrodes of high transparency and thermal stability upto 85% and 500°C respectively.

Description

TITLE: A HYBRID TRANSPARENT CONDUCTING ELECTRODE AND METHOD THEREOF

TECHNICAL FIELD

The present invention is in relation to the field of nanotechnology. In particular to the technology of hybrid Transparent Conducting Electrode (TCE). The invention provides facile a method for fabrication of hybrid Transparent Conducting Electrodes comprising Aluminium mesh, Tin (IV) oxide; and handles cost competitiveness effectively. The method facilitates the fabrication of transparent electrodes of high transparency and thermal stability upto 85% and 500°C respectively. The large area processability of transparent electrode augments the advantage of the invention.

BACKGROUND

Research related to Transparent Conducting Electrodes is in full swing owing to its competence for adoption in electrochromic devices, solar cells, organic light emitting diodes, supercapacitors, liquid crystal displays and other optoelectronic devices. The research spans over nature of materials, their abstemious usage and mode of adoption for developing cost competitive TCEs exalted in optoelectronic properties.

Metal oxides has been the cynosure of the research, various metal oxides like Indium tin oxide, Fluorine tin oxide, Aluminium zinc oxide have been tested and used exclusively or along with other conductors by various methods. Shihui Yu et al has discussed about tri layered hybrid conducting electrodes using Copper and Silver metal along Tin oxide. “Characterization of Tin (IV) oxide 2/Cu/Tin (IV) oxide 2 multi layers for high performance transparent conducting electrodes’; Thin Solid Films 562 (2014) 501-505 discuss about the adoption of Copper with Tin oxide and “Optimization of Tin (IV) oxide 2/Ag/Tin (IV) oxide 2 tri- layer film electrode with high figure of merit” Thin Solid Films 552 (2014) 150-154 informs about Silver with Tin(IV) oxide.

However, known methods restrict the fabrication of TCE to small areas owing to its cost, mechanical properties and mode of fabrication. The restrictions impose a need for developing a fabrication method that overcome large area processability and provide TCEs with good optoelectronic properties, thermal stability and economical.

The present invention aims to provide a facile and cost-effective method for the fabrication of the Transparent Conducting Electrodes with good optoelectronic properties and thermal stability. SUMMARY OF INVENTION

Accordingly the present invention provides a method for fabrication of hybrid transparent conducting electrode(A) comprising Aluminium mesh (7) and film of Tin(IV) oxide(10)film on a substrate(l) by adopting a facile and cost effective method.

The method of fabrication comprise steps of depositing Aluminium in a crackle template, washing the template, heating the substrate to 500°C to get a coating of Aluminium oxide on

Aluminium mesh (7) and depositing a layer of Tin(IV) oxide film (10) on the substrate (1) maintained at 500°C.

The invention also provides a method of patterning of hybrid transparent conducting electrode(A). BRIEF DESCRIPTION OF FIGURES

The present invention can be understood by the following description in conjunction with the accompanying figures, which however should not be taken to limit the disclosure to the specific embodiments, but are for explanation and understanding only. Figure 1: shows the schematic diagram of the fabrication of hybrid transparent conducting electrode (A). Inset of (V) is a digital photograph of the final electrode.

Figure 2: shows the change in resistance of (a) bare Aluminium mesh and (b) Tin (IV) oxide coated Aluminium mesh, with the change in their ambienttemperature, confirming that they regain their initial resistance after cooling down to 23±2°C from 500 °C, (c) change in their resistances due to continuous heating at 500 °C for 80 minutes, showing almost no increment in resistances, (d) IR image showing the temperature on the two electrode surfaces to be 500 °C, (e) and (f) digital photographs of the electrodes while heating at high temperature in air.

Figure 3: shows the mechanical stability of TCE of current invention by Scotch tape adhesion test: (a) plot, showing the change in resistances of the bare A1 mesh (red) and Tin

(IV) oxide coated Aluminium mesh (black), for the cyclic scotch tape peeling off test. Stability plot, (b) for bare A1 mesh, showing more than 3000% resistance change just after 20 cycles, and (c) for Al/Tin (IV) oxide, showing only 8% change even after 1000 peeling off cycles. Pencil hardness test: (d) change in resistances of both the electrodes due to scratching by the pencils of different hardness (from H to 6H). (e) Comparison plot of resistance change for the cyclic scratching by a 6H pencil (f) Resistance change fitting profile for Al/Tin (IV) oxideelectrode during the cyclic pencil hardness test. Figure 4: shows (a) Schematic representation of pattering steps of the hybrid TCE by projection lithography: (i) irradiation of a pattern drawn in a power point file, through a combination of projector and lens focused on the Photo resist(PR) coated hybrid TCE and PR development (ii) chemical etching of the Tin (IV) oxide film at the exposed area by Zn power and HC1. (iii) A1 etching in an A1 etchant solution (H3PO4 (80%) + CH3COOH (

5%) + HNO3 (5%) + H2O (10%)). (iv) removal of photo resist and cleaning of the pattaerned TCE. (b): (i)-(iv) optical images and (c) (i)-(iv) cross sectional schematics of the same described in (a): (i)-(iv). (Scale bar 200 pm)

Figure 5: shows SEM images of (a) A1 mesh (b) Sn02 coated A1 mesh and (c) ITO and it is clear from the images that there is charging effect on bare A1 mesh TCE, however in the case of Al/Sn02, no charging effect observed.

DETAILED DESCRIPTION OF INVENTION

The foregoing description of the embodiments of the invention has been presented for the purpose of illustration. It should not be construed that the scope of the invention is limited to the disclosure herein.

The various embodiments of the transparent conducting electrode of the present invention along with its method of preparation/fabrication are described below with reference to the figures.

It may further be noted that as used herein and in the appended claims, the singular forms "a", "an", and "the" include plural reference unless the context clearly dictates otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by person skilled in the art. The present invention provides a fabrication method for large area hybrid transparent conducting electrode (A) based on Aluminium mesh (7) coated with an oxide layer of Tin(10) by spray coating; over a substrate (1). The hybrid transparent conducting electrode(A) provide transparency upto 85%, exhibit sheet resistance of about 5Q/sq and large size of about 15x15 cm . The raw materials adopted in the fabrication method and method per se render the hybrid transparent conducting electrode economical and industry compatible.

Definitions:

Crackle-A crack in a film coated on a substrate, wherein the crack is deep down to the substrate.

Typically the invention comprise fabrication of hybrid transparent conducting electrode by steps comprising (i) preparation of interconnected crackle template on a substrate; deposition of Aluminium in the crackle template, removing the crackle template to get Aluminium mesh; heating the Aluminium mesh at 500°C for about 5 minutes for the formation of Aluminium oxide (AI₂O₃) shell layer of enough thickness to protect the

Aluminium from corrosion during the process of getting the Tin (IV) oxide coating using hydrated Tin(II) chloride precursor by spray coating.

A hybrid transparent conducting electrode of size 10x10 cm fabricated according to the current method (Figure 1) is adopted to test various parameters like for example -sheet resistance, transmittance, heating profile and mechanical stability; which exhibited more than 85% transmittance and sheet resistance 5Q/sq. I. Fabrication of Aluminium mesh on a substrate

Raw materials:

A sacrificial crackle precursor from a group of precursors such as: crackle paints, acrylic resin dispersion, Ti(¾ nanoparticles-based dispersion, milk powder, egg white and the like which form fine cracks upon drying, is selected for obtaining the crackle template.

Substrate is selected from a group comprising glass, mica, Polyethylene terephthalate(PET) and the like.

General Procedure:

A sacrificial crackle precursor is sprayed on a clean transparent substrate (1) (glass) to form a uniform thin film (2) of the precursor (3) (Figure 1 (i), which upon drying form an interconnected micro-crackle network (5) to be used as a template for metal deposition (Figure (ii)). To get a uniform thin film of the precursor, parameters like precursor concentration, flow rate, (X,Y) speed, temperature of the substrate while spraying, distance between the substrate and the spray head of the spray gun(4), pressure are varied and optimized to get crackle (6) width thickness ranging from 50 to 1000 nm.

Aluminium is deposited on the template by physical vapour deposition (PVD). After removal of the template by water and drying, an Aluminium mesh (7) transparent conducting electrode with a transmittance of about 93% at a sheet resistance of about 5 ohm/sq is obtained (see Figure (iii)) for a metal thickness of 300-400 nm. However, the

Aluminium metal thickness can be varied from few tens of nanometers to hundreds of nanometers as per the requirement of sheet resistance. Thickness of the Aluminium oxide (Alumina) layer on Aluminium metal is 3-4 nm.

II. Fabrication of Tin (IV) oxide 2 film on Aluminium mesh on a substrate.

General Procedure: The Aluminium mesh is kept at 500 °C for 5 minutes for formation of Aluminium oxide

(AI₂O₃) shell layer of enough thickness(3- 4 nm) so that it can protect the Aluminium from getting corroded during the spray coating.

A thin Tin (IV) oxide layer over the Aluminium mesh is obtained by spraying coating, a SnCl₂.2H₂0 (hydrated Tin(II)chloride) solution (9) in ethanol at a concentration of 0.05M - 3M, while keeping the substrate at 500 °C.A spray-pyrolysis equipment with syringe pump and a heater (8) having heating capability up to 550 °C is adopted to get a conducting overlay ofTin (IV) oxide on Aluminium mesh (10) ( Figure l(iv)).The compact Aluminium oxide shell layer on Aluminium mesh would be impermeable to HC1 vapours produced during conversion of Tin (IV) oxide from Tin(II) chloride; or air, thus rendering stability to the Aluminium mesh at temperature as high as 500°C.

Conducting overlay coating:

Tin Oxide (Sn0₂), Zinc Oxide (ZnO), conducting polymer (PEDOT:PSS) overlay coatings are tried. Tin Oxide (Sn0₂) is preferred over other oxide layers due to it better conductivity, high transparency and stability.A precursor solution which is chosen from a group of precursor solutions selected from SnCl₄.2H₂0 or SnCl₂.2H₂0 dissolved in ethanolis sprayed on the metal mesh using a spray -pyrolysis equipment with syringe pump and heated at a 500°C to get a conducting overlay on mesh (Figure l(iv)).

Parameters:

Various parameters adopted and optimised for the fabrication of the hybrid transparent conducting electrode with good optoelectronic properties is summarised in the table- 1.

Table 1: Parameters adopted for the fabrication of hybrid Transparent Conducting electrode.

The temperature as high as 500°C for the method is astutely adopted and optimised. While spray coating, the substrate temperature cannot be kept below 450 °C, as Tin(II) chloride to Tin (IV) oxide conversion occurs above this temperature and if the temperature is maintained lower, the metal mesh gets corroded within seconds since the precursor solution for Tin (IV) oxide coating is highly corrosive and can corrode almost all metals including Aluminium metal. Therefore, the Aluminium mesh structure has to be stable even at such high temperature and corrosive condition. At 500 °C, as the Tin(II) chloride solution before reaching the substrate surface will be converted into Tin (IV) oxide and thus the exposure to corrosive gases like hydrogen chlorideis avoided. Also, it is found that Tin (IV) oxide film deposited at about 500 °C provides comparatively better opto electronics properties.

Various metals were studied to optimize for the fabrication. Tin (IV) oxide film is coated on metal meshes like Silver, Copper, Tin, Gold, Aluminium and the like. It is observed that in the case of Silver, Copper and Tin the meshes became non-conducting when the temperature is increased to 200 °C. Gold and Aluminium are found to be stable beyond

500 °C and thus the Tin (IV) oxide coating is tried only on these two metal meshes. However, to leverage the cost of the hybrid transparent conducting electrode Aluminium is chosen for all experimentation.

Tin (IV) oxide film’s smoothness is also an important parameter for a transparent conducting electrode. Hydrated stannous chloride dissolved in ethanol is chosen as the precursor, as it produces a very compact and smooth Tin (IV) oxide film, unlike dehydrated stannous chloride, which gives a rough film when sprayed on mesh. The compressed air pressure is kept in the range from 0.4 to 2 bar because, a pressure below 0.4 bar will produce non-uniform spray of the solution and pressure above 2 bar will create such a high airflow that it can cool down the top surface of the substrate. Thus, the temperature difference that gets created between the top and bottom surface of glass, which is kept at 500 °C can cause the glass (if used as substrate) to break.

The flow rate range is maintained between 0.1-5 ml/minute because, rate below this will create non-uniform Tin (IV) oxide film and rate above this causes the glass to break (if used as substrate).

The spray coating (spraying) to obtain Tin (IV) oxide film is carried out for about 5 minutes to get a film thickness of 200-300 nm longer coating time can cause the mesh to get corroded due to the high exposure of HC1 vapours. After the coating, the Tin (IV) oxide coated mesh is annealed for longer time to get better crystallinity of Tin (IV) oxide film. After the annealing, the temperature of the substrate is cooled down to below 200 °C and kept inside a water bath for 15 minutes to wash away the residual HC1, if any, present on the substrate to avoid corrosion.

The precursor solution coating to obtain Tin (IV) oxide film is tried by methods such as spin coating, dip coating along with spray coating. However, except in spray coating, other methods rendered the mesh unstable as the process temperature cannot be kept around 500 °C and longer exposure to the Tin(II) chloride solution got the mesh corroded. III. Study of Thermal stability:

Vulnerability to high temperature is the most commonly encountered issue for a TCE during the fabrication of photovoltaic devices as it needs high temperature for the electron transport layer (ETL) coating and to ascertain the ability of present electrode on sustenance of higher temperature, thermal stability experiments are performed on both bare Aluminium mesh and SnC>2 coated Aluminium mesh electrodes and the corresponding results are shown in Figure 2 (a)-(c). The thermal studies of the hybrid conducting electrode indicate that the electrodes are thermally very stable. The stability is analysed by a multi-meter and an IR camera. The temperature of the substrate is monitored by the IR camera while the resistance is checked at different temperatures using the multi-meter. The variation is then plotted to check the stability of the electrode. Typically, temperature of both the electrodes is first increased up to 500 °C from about 23±2°C and continued heating at 500 °C for 80 minutes and then cooled down to 23±2°C.

As shown in Figure 2 (a) and (b), the resistances of both the electrodes increased linearly with temperature, a well-known behavior for metallic electrodes, and regained their initial resistances after cooling back to 23±2°C. The calculated thermal coefficient of resistivity (TCR) during heating and cooling are 0.0025 /°C and 0.0033 /°C respectively, which are slightly lesser than the bulk TCR value (0.0038 /°C) and this could be attributed to the reduced electron-phonon coupling in the metallic thin film since the thickness of Aluminum here is few hundreds of nanometer. Also, when the electrodes are heated continuously at 500 °C in air for 80 minutes, there is almost no change in resistances (Figure 2 (c)), confirming the electrodes to be highly stable at higher temperature and the stability is believed to be highest among all other nanowires of Ag, Cu, Ni, Au and the like or metal mesh-based electrodes (Table 2). The thermal stability at higher temperature is attributed to the presence of an alumina shell layer of thickness about 3-4 nm, which prevent the core aluminum from getting further oxidized, acting as a shield for the air to diffuse through. Figure 2 (d) and (e)-(f) are an IR image showing the surface temperature on the two electrode surfaces to be 500 °C and digital photographs of the electrodes while heating at high temperature, respectively. The comparative analysis of thermal stability of TCE discussed in various literature with that of present invention is provided in Table

2. Table 2:Comparative analysis of thermal studies of TCE obtained by current method with known TCE in literature.

IV. Study of Mechanical stability:

To check the mechanical durability of the electrodes, scotch tape adhesion test and pencil hardness scratch-proof test are performed. Figure 3 (a)shows the change in resistances of the bare Aluminium mesh (red) and Tin (IV) oxide coated Aluminium mesh (black), for the cyclic scotch tape peeling off test, and figure 3(b)shows the stability plot for bare A1 mesh, which indicate more than 3000% resistance change just after 20 cycles. The bare A1 mesh could not sustain the scotch tape peeling off test as the resistance increased by more than 35 times to its initial value just after 20 cycles and this might be due to the weaker adhesion of aluminum to the glass surface. However, the hybrid electrode shows a very high solidity against the peeling off, as the change in its resistance is only 0.08% (Figure 3 (c)) even after 1000 cycles and the reason could be due to the strong adhesion between glass and the SnC>2 thin film protecting the Aluminium mesh from a direct contact with the scotch tape. The curve in Figure 3 (c) follows a logarithmic fitting, probably due to the initial harm to the metal mesh at the few defected spots present on the

Sn02 film. To further examine the scratch-proof of the electrodes, the results of pencil hardness tests are shown in Figure 3 (d)-(f). Plot in Figure 5(d) depict that even a 3H pencil could able to scratch the bare A1 mesh and thereby there is an increment in resistance by more than 100%, whereas the change is almost negligible for SnC>2 coated Aluminium mesh electrode even after the 6H pencil scratch test. A cyclic stability test is performed on the electrodes using a 6H pencil by scratching at a particular place on the electrode repeatedly and the result is shown in Figure 3 (e)-(f). The result describes that just after 4 scratching cycles, the bare Aluminium mesh electrode became almost non- conducting, whereas the resistance of the hybrid electrode increased only by 3 times to its initial resistance after 20 cycles of scratching and 15 times after 30 cycles. The results confirm that SnC>₂ overlay is not only required to fill the non-conducting regions of the TCE by a conducting film, but also to improve the mechanical stability of the electrode. V) Pattering of the hybrid TCE by projection lithography:

A unique patterning process is developed as described in the schematic representation in Figure 4(a) and 4(c) by projection lithography followed by a chemical etching. The steps involve drawing a desired pattern in a PowerPoint file and then projecting on a positive photoresist (PR)( 11) selected from a list comprising AZ 1505, AZ 1512 HS, AZ 1514 H, AZ 1518, AZ 1518 HS, preferably AZ1512HS coated hybrid electrode using a computer(13) and a projector focusing through a set of convex lenses in a micrometer range (Figure 4(a)(i)). The UV light from a UV source(12) projector soften the irradiated area of PR. The substrate is then put into developer solution kept in a petri dish(14) to remove PR from the exposed region as shown in the optical microscopy image in Figure 4(b)(i) and the cross-sectional schematic Figure 4(c)(i). In the second step the top Tin (IV) oxide layer is removed from the exposed region, the PR coated electrode is dipped in a dilute hydrochloric acid (HC1:H₂0 :: 1:2, 50%) and Zinc powder (about 0.5g to about 5g) is sprinkled slowly at 25 °C, resulting in the etching of Tin (IV) oxide completely from the expossed region (Figure 4 (a)(ii), optical microscopy image Figure 4(b)(ii) and the cross-sectional schematic Figure (c)(ii)). Fater in the third step, the electrode is dipped in a standard Aluminum etchant solution compising Phosphoric acid (H₃PO₄-80%), Acetic acid (CH₃COOH -5%), Nitric acid(HN0₃-5%) and Water ( ¾0 -10%) for 90 seconds to etch out the Aluminium mesh (thickness 400 nm) completely as shown in the schematic in Figure 4(a)(iii), (c)(iii) and the optical microscopy image in figure 4(b)(iii)). The etchant solution is selected for a slow and controlled Aluminium etching. The PR is then removed in Acetone to yield a micro-patterned hybrid mesh (Figure 4(a)(iv), the optical microscopy image is shown in figure 4(b)(iv), and the cross-sectional schematic in figure 4(c)(iv)). VI) Electric field driven device performance (advantage over only metal mesh):

The disadvantage of bare metal mesh is its charging effect during SEM imaging, which has been shown in figure 5 (a). Due to the presence of more than 80% non-conducting region on the TCE, it is not able to distribute or dissipate the electrons uniformly and as a result, the acquired SEM image is distorted and thus not clear. This lead to non-efficient and non-uniform charge collection or injection in solar cells or LEDs, no proper switching of transparency in voltage driven smart windows (e.g. - Electrochromic, polymer dispersed liquid crystal and the like). In contrast, a thin conducting coating of SnC>2 on Aluminium mesh provide solution and this can be concluded from the SEM image in figure 5 (b), where no charging effect is observed and this effect is similar to the ITO surface which has been shown in figure 5 (c) depicting no charging effect or distortion in the image.

Table 3 provides comparative analysis of the hybrid transparent conducting electrode of present invention with trilayered hybrid transparent metal electrode disclosed in the literature with Tin (IV) oxide coating i.e., Shihui Yu et al “Characterization of Tin (IV) oxide 2/Cu/Tin (IV) oxide multilayers for high performance transparent conducting electrodes’; Thin Solid Films 562 (2014) 501-505 and Shihui Yu et al “Optimization of Tin (IV) oxide /Ag/Tin (IV) oxide 2 tri-layer film electrode with high figure of merit” Thin Solid Films 552 (2014) 150-154, clearly highlight the advantage of present method.

Table 3: Comparative analysis of TCE obtained by current method and literature documents.

Thus the present invention provides a unique method that help in fabrication of hybrid transparent electrode with good opto electronic properties. The method embraces cost effective materials and mode of fabrication which is industry scalable in terms of the size/area and optoelectronic properties of Transparent conducting electrode.

Claims

WE CLAIM:

1.A method of fabrication of hybrid transparent conducting electrode(A) comprising Aluminium mesh (7) and Tin(IV) oxide layer(lO) on a substrate(l), said method comprising steps of a) depositing Aluminium in crackles of a film (2) on a substrate (1) and drying; removing the dried film (5) to obtain the substrate deposited with Aluminium mesh(7); b)heating the substrate (1) to a temperature of 500°C for 5 minutes to obtain a coating of Aluminium oxide on the Aluminium mesh; and c) coating a layer of Tin (IV) oxide (10) by spraying solution of hydrated Tin (II) chloride at

500°C over the substrate deposited with Aluminium oxide coated Aluminium mesh, to obtain the hybrid transparent conducting electrode.

2. The method of fabrication as claimed in claim 1, wherein the film is of material selected from a group comprising crackle paints, acrylic resin dispersion, Tί(¾ dispersion, milk powder, egg white, and the like.

3. The method of fabrication as claimed in claim 1, wherein the film is removed by washing with water.

4. The method of fabrication as claimed in claim 1, wherein the spraying solution of hydrated

Tΐh(P) chloride is in ethanol or water.

5. The method of fabrication as claimed in claim 4, wherein the solution of hydrated Tin(II) chloride is of concentration ranging from 0.05M to 3M.

6. A hybrid transparent conducting electrode (A) comprising Aluminium mesh (7) and Tin(IV) oxide layer(lO) on a substrate(l).

7. The hybrid transparent conducting electrode as claimed in claim 6, wherein the Aluminium mesh is coated with Aluminium oxide.

8. The hybrid transparent conducting electrode as claimed in claim 6, wherein the Aluminium mesh is of thickness ranging from 50 to 1000 nm, Aluminium oxide is of thickness ranging from 3 to 4 nm and Tin(IV) oxide layer is of thickness ranging from 200nm to 300nm.

9. The hybrid transparent conducting electrode as claimed in claim 6, wherein the electrode provides thermal stability up to 500°C, transmittance of 85% and sheet resistance of 5 Ohm/Sq.

10. The hybrid transparent conducting electrode as claimed in claim 6, wherein the Tin (IV) oxide provides mechanical stability and uniform charge transport.

11. A method of patterning hybrid transparent conducing electrode comprising Aluminium mesh and Tin(IV) oxide layer on a substrate, said method comprising acts of- a) drawing a desired pattern and projecting on a photoresist (PR) coated hybrid transparent electrode; b)illuminating the photoresist coated hybrid transparent electrode with UV light; and c) dipping the photoresist coated electrode in dilute hydrochloric acid and adding Zinc powder to remove Tin (IV) oxide from the illuminated region followed by dipping in a solution comprising Phosphoric acid (80%), Acetic acid (5%), Nitric acid (5%) and Water (10%)) to remove the Aluminium mesh to obtain the patterned hybrid transparent conducing electrode comprising Aluminium mesh and Tin(IV) oxide layer on a substrate.

12. The method of patterning hybrid transparent conducing electrode as claimed in claim 11, wherein the photoresist is selected from a group comprising AZ 1505, AZ 1512 HS, AZ 1514 H, AZ 1518, AZ 1518 HS.

13. The method of patterning hybrid transparent conducting electrode as claimed in claim 11, wherein the hydrochloric acid is of 50% concentration and Zinc powder ranging from 0.5g to

5g·