A non-noble metal-doped myriophyllum-derived carbon-based material with oxygen reduction activity and its application

Abstract

The present invention belongs to the field of inorganic functional materials and electrochemical energy technology, and specifically relates to a non-precious metal-doped foxtail algae-derived carbon-based material with oxygen reduction activity and its application. The preparation method of the carbon material comprises the following steps: S1: culturing the biomass foxtail algae in a water environment containing metal components; S2: removing the water after washing the product in the above S1; S3: grinding the dried foxtail algae in the above S2 into powder; S4: adding an external nitrogen source to the powder in the above S3 to obtain a metal-nitrogen composite biomass material precursor; S5: heat-treating the precursor in the above S4 in a tubular furnace under inert gas protection to obtain a foxtail algae-derived carbon-based material. The carbon-based material provided by the present invention has excellent performance, can be used to prepare the oxygen reduction electrode of a fuel cell, and can be used in a fuel cell, and shows good electrochemical performance, and has great application potential and industrial value in the field of electrochemistry.

Description

Technical Field

[0001] The present invention belongs to the technical fields of inorganic functional materials and electrochemical energy, and particularly relates to a non-precious metal-doped carbon-based material derived from Myriophyllum spicatum with oxygen reduction activity and its application. Background Art

[0002] Electrochemical energy conversion and storage devices such as fuel cells, unitized regenerative fuel cells (URFCs), and rechargeable metal-air (oxygen) batteries are key nodes in the development and utilization of renewable energy. These devices use the oxygen reduction reaction (ORR) at the cathode of fuel cells and during the discharge process of metal-air batteries. The performance of fuel cells and metal-air batteries is significantly limited by the slow ORR kinetics. Therefore, both academia and industry have made great efforts to develop advanced electrocatalysts and / or electrode materials for the cathodes of these devices. The state-of-the-art ORR catalysts are materials based on platinum group metals (PGMs).

[0003] However, the biggest challenge faced by PGM-based ORR catalysts is the scarcity and high cost of PGM resources. Therefore, a great deal of effort has been devoted in the past few decades to developing advanced PGM-free ORR catalysts.

[0004] Two of the most representative PGM-free ORR catalysts, heteroatom (e.g., N)-doped carbon and transition metals (e.g., Fe) coordinated with N in the carbon matrix have been widely accepted as promising candidates to replace PGM-based materials. In both cases, carbon is the main component; even for PGM-based ORR catalysts, the carbon support is an important research topic. Therefore, the research on carbon supports is crucial for the research and development of PGM-free ORR catalysts. Different types of carbon precursors have been used to synthesize PGM-free ORR catalysts, such as metal-organic framework-derived carbon, carbon black, and graphene. In particular, biomaterials (i.e., biomass) have recently emerged as promising carbon precursors. This is based on the renewable and sustainable characteristics of biomass, resulting in abundant raw material sources, i.e., low cost. In addition, due to the need for biology to adapt to various natural environments, biomass has many interesting characteristics in terms of composition and structure. Therefore, biomass materials have a large number of elements required to construct ORR active sites and some unique coordination environments. It should be mentioned that, in addition to active sites, mass transfer is another key parameter determining ORR performance. The mass transfer problem can be easily alleviated by using porous electrocatalysts and electrodes. In this regard, biomass materials with well-organized macro, meso, and microstructures are expected to provide customizable templates for material synthesis.

[0005] Porous carbon materials with excellent oxygen reduction activity, including biomass materials doped with non-precious metals, have been widely used in fuel cells, for example:

[0006] CN110575834A discloses a rare earth-doped iron-based catalyst, its preparation method and application. The raw materials of the rare earth-doped iron-based catalyst consist of the following components: iron nitrate, rare earth compound and diatomite, wherein: the molar ratio of iron nitrate to rare earth compound is (1-6):1, and the mass ratio of iron nitrate to diatomite is 1:(0.3-6); the rare earth-doped iron-based catalyst is prepared according to the following method. Mix iron nitrate and rare earth compound evenly, add deionized water and stir to dissolve it to obtain a mixed solution, wherein the concentration of iron nitrate in the mixed solution is 0.1-2 mol / L; mix diatomite with the mixed solution and stir, place it in an ultrasonic generator and ultrasonically load for 0.5-1 h, and then stand at room temperature for 12 h; after extrusion molding and drying, calcine in a rich oxygen atmosphere or a mixed atmosphere of sulfur dioxide and air at 300-600 °C for 2-5 hours, and cool naturally to obtain the rare earth-doped iron-based catalyst. The rare earth-doped iron-based catalyst not only has excellent high-temperature stability, but also has a wide temperature application range.

[0007] CN103007975A discloses a preparation method of a high-nitrogen-containing carbon material, belonging to the technical field of carbon composite materials. The technological steps are as follows: 1. Dry and ball-mill soybeans to obtain soybean powder; 2. In a protic solvent, mix soybean powder and chloride salt at a certain mass fraction, ultrasonically disperse and stir for a period of time, and evaporate the solvent to obtain a mixed solid powder; 3. Ball-mill the mixed solid powder in a zirconia ball-milling tank; then place the ball-milled powder in a tubular furnace and carbonize it under the protection of high-temperature inert gas to obtain a primary carbonized material; 4. Continue to ball-mill the primary carbonized material in a zirconia ball-milling tank, fully disperse it in acetone, and reflux for a period of time at a certain temperature; filter, wash with deionized water and dry, oxidize it with a mixed aqueous solution of nitric acid and hydrogen peroxide at room temperature, then wash, filter, dry to obtain a secondary carbonized material; 5. Place the secondary carbonized material in a tubular furnace and continue to carbonize it under the protection of high-temperature inert gas; then oxidize it with a mixed aqueous solution of nitric acid and hydrogen peroxide at room temperature, wash, filter, dry and grind to obtain a non-precious metal oxygen reduction electrocatalyst. The high-nitrogen-containing carbon material prepared by this method as an oxygen reduction catalyst has the advantages of good stability, high activity, not being easily poisoned, etc. More importantly, the raw materials used in the preparation of the above carbon material are not precious metals, realizing the non-precious metalization of the oxygen reduction catalyst in fuel cells, thus greatly reducing the cost of the oxygen reduction catalyst and being beneficial to the industrialization of fuel cells.

[0008] CN109148901A discloses a doped carbon-based transition metal oxide composite material, a preparation method thereof and an application thereof. The preparation method includes: adding sodium alginate into deionized water, and obtaining a transparent viscous liquid after stirring; adding a sulfur and nitrogen source into a transition metal solution, and obtaining a homogeneous solution after stirring; dropping the transparent viscous liquid into the homogeneous solution, stirring and standing to obtain a tubular coagulated hydrogel; filtering, washing and freeze-drying the tubular coagulated hydrogel to obtain a dry gel; carbonizing the dry gel under an inert atmosphere to obtain a pyrolysis clinker; heat-treating the pyrolysis clinker under an air atmosphere, and then washing and drying to obtain a doped carbon-based transition metal oxide composite material, which can be used as a bifunctional catalyst for the air electrode positive electrode of a zinc-air battery.

[0009] CN112436155A discloses an oxygen evolution reaction catalyst of Co / N double-doped biomass porous carbon spheres. Using lignin microspheres as a biomass carbon source and adding an additional N source, N-doped porous carbon spheres are obtained by carbonization, which have a rich mesoporous structure and a super-high specific surface area. Co2+ is thermally reduced to form Co nanoparticles, which are highly dispersed in the matrix of the N-doped porous carbon spheres, reducing the agglomeration and aggregation of Co nanoparticles. The uniformly dispersed Co nanoparticles can better form Co-Nx active sites with adjacent active nitrogen structures, serving as the active catalytic center for the oxygen evolution reaction. Under the synergistic effect of the porous carbon sphere matrix and the highly dispersed Co-Nx catalytic active center, the oxygen evolution reaction catalyst exhibits a high oxygen evolution onset potential and an oxygen evolution half-wave potential, and has excellent oxygen evolution reaction catalytic activity.

[0010] CN112892593A discloses a MOFs / water hyacinth-derived material, a preparation method thereof and a method for degrading organic pollutants. The MOFs / water hyacinth-derived material is composed of water hyacinth biochar and cobalt-based zeolitic imidazolate frameworks embedded in the water hyacinth biochar. The water hyacinth biochar serves as the carrier of the MOFs material. The prepared MOFs / water hyacinth-derived material has excellent stability, conductivity and specific surface area, which is more conducive to the charge transfer and mass transfer process between the cobalt active sites and the pollutants; due to the pore-limiting effect of the water hyacinth biochar, the crystal growth of the MOFs-derived metal oxides during thermal decomposition can be effectively restricted. The MOFs / water hyacinth-derived material of this application has a strong ability to activate persulfate to generate sulfate radicals, enabling it to have a high-efficiency and long-lasting ability to catalytically oxidize organic substances, effectively overcoming the disadvantages such as easy agglomeration of the catalyst and long activation time of persulfate.

[0011] As described above, a variety of metal-doped biomass-derived composite materials have been disclosed in the prior art. Due to the introduction of metals, the resulting carbon-doped materials (such as carbon nanotubes, mesoporous carbon, graphene, etc.) exhibit excellent ORR and OER activities. However, on the other hand, the synthesis process of such catalysts is complex, the conditions are harsh, it is difficult to carry out large-scale synthesis, and their bifunctional electrical properties still need to be further improved.

[0012] For the above reasons, it is still of great significance to synthesize new non-precious metal-doped biomass-derived carbon-based materials with good electrical properties through simple, green, and low-cost methods. This is also a research hotspot and focus in the field of electrochemical energy at present, and this is exactly the basis and driving force for the completion of the present invention. Summary of the Invention

[0013] In order to develop new non-precious metal-doped biomass-derived carbon-based materials, especially porous carbon materials for oxygen reduction electrodes, the inventors of the present invention have conducted in-depth research. After a large amount of creative work, the present invention has been completed.

[0014] Specifically, the technical solution and content of the present invention relate to a non-precious metal-doped Myriophyllum spicatum-derived carbon-based material with oxygen reduction activity, an oxygen reduction electrode and its preparation method, and a fuel cell.

[0015] More specifically, the present invention relates to the following aspects.

[0016] In the first aspect, it relates to a non-precious metal-doped Myriophyllum spicatum-derived carbon-based material with oxygen reduction activity. The preparation method of the carbon material includes the following steps:

[0017] S1: Cultivate the biomass Myriophyllum spicatum in an aqueous environment containing metal components;

[0018] S2: After washing the product in S1 above, remove the moisture;

[0019] S3: Grind the dried Myriophyllum spicatum in S2 above into powder;

[0020] S4: Perform external nitrogen source doping on the powder in S3 above to obtain a metal-nitrogen composite biomass material precursor;

[0021] S5: Heat-treat the precursor in S4 above in a tubular furnace under the protection of an inert gas to obtain a Myriophyllum spicatum-derived carbon-based material.

[0022] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S1, the metal component-containing water environment includes one or more of iron, nickel, cobalt, copper, and zinc metal ions, and the source comes from various metal inorganic salts. For example, the iron salt can be ferric nitrate, ferric sulfate, iron acetylacetonate, ferrocene, or ferric chloride.

[0023] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S2, the dehydration includes one of hot drying, natural drying, and freeze-drying.

[0024] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S2, the drying temperature is 60-120 °C, for example, it can be 60 °C, 80 °C, 100 °C, or 120 °C; the drying time is 4-12 hours, for example, it can be 4 hours, 6 hours, 8 hours, 10 hours, or 12 hours.

[0025] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S3, the grinding method can be mechanical stirring, ball milling, and grinding with an ordinary mortar.

[0026] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S4, the external nitrogen source doping method can be ball milling and impregnation.

[0027] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S4, the ball milling speed is 300-700 rpm / min, for example, it can be 300 rpm / min, 400 rpm / min, 500 rpm / min, 600 rpm / min, or 700 rpm / min; the ball milling time is 2-12 hours, for example, it can be 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, or 12 hours.

[0028] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S4, the mass ratio of the external nitrogen source to the myriophyllum powder is any ratio of 1:1 - 1:4, for example, it can be 1:1, 1:2, 1:3, or 1:4.

[0029] In the preparation method of the non-precious metal-doped myriophyllum-derived carbon-based material of the present invention, in step S5, the inert gas includes nitrogen and argon.

[0030] In the preparation method of the non-noble metal-doped myriophyllum-derived carbon-based material of the present invention, in step S5, the heat treatment temperature is 700 °C - 1100 °C, for example, it can be 700 °C, 800 °C, 900 °C, 1000 °C or 1100 °C, preferably 800 - 1000 °C, and most preferably 800 °C.

[0031] In the preparation method of the non-noble metal-doped myriophyllum-derived carbon-based material of the present invention, the time for heat treatment in the tubular furnace is 1 - 4 hours, for example, it can be 1 hour, 2 hours, 3 hours or 4 hours.

[0032] The inventors of the present invention found that when the above preparation method of the present invention, especially certain preferred process parameters thereof, is adopted, a non-noble metal-doped myriophyllum-derived carbon-based material with excellent oxygen reduction activity can be obtained. The oxygen reduction electrode prepared therefrom has excellent electrochemical properties, such as high catalytic activity, good stability, long service life, etc., and thus can be applied to the field of fuel cells.

[0033] In a second aspect, the present invention also relates to an oxygen reduction electrode, and the oxygen reduction electrode comprises the non-noble metal-doped myriophyllum-derived carbon-based material.

[0034] In a third aspect, the present invention also relates to a preparation method of the oxygen reduction electrode, and the method comprises the following steps:

[0035] A. Polish the glassy carbon electrode in an alumina aqueous slurry with a particle size of 1 - 0.05 μm, then ultrasonically wash it in acetone, absolute ethanol and high-purity water for 20 - 60 seconds in sequence, and dry it with nitrogen to obtain a pretreated glassy carbon electrode;

[0036] B. Take the non-noble metal-doped myriophyllum-derived carbon-based material in a mixed solution of ethanol, water and Nafion, then ultrasonically disperse it for 30 - 60 minutes to obtain a uniformly mixed solution; drop the uniformly mixed solution onto the pretreated glassy carbon electrode and dry it at room temperature to obtain the oxygen reduction electrode.

[0037] In the preparation method of the oxygen reduction electrode of the present invention, in step A, the diameter of the glassy carbon electrode is 2 - 6 mm, for example, it can be 2 mm, 3 mm, 4 mm, 5 mm or 6 mm.

[0038] In the preparation method of the oxygen reduction electrode of the present invention, in step A, the high-purity water is deionized water, and preferably its resistance is at least 18 MΩ.

[0039] In the preparation method of the oxygen reduction electrode of the present invention, in step A, there is no clear regulation on the dosages of the acetone, absolute ethanol and high-purity water, and those skilled in the art can make appropriate selections, for example, dosages that can fully immerse the glassy carbon electrode and facilitate washing are sufficient.

[0040] In the preparation method of the oxygen reduction electrode of the present invention, in step B, the mass percentage concentration of the ethanol aqueous solution is 30-60%, for example, it can be 30%, 40%, 50% or 60%.

[0041] In the preparation method of the oxygen reduction electrode of the present invention, in step B, ultrasonic dispersion is carried out for 30-60 minutes, for example, it can be 30 minutes, 40 minutes, 50 minutes or 60 minutes, and preferably 60 minutes.

[0042] In the preparation method of the oxygen reduction electrode of the present invention, in step B, the mass volume concentration of the non-precious metal doped Myriophyllum-derived carbon-based material in the uniformly mixed solution is 3-6 mg / ml, that is, each 1 ml of the uniformly mixed solution contains 3-6 mg of the nitrogen and sulfur co-doped cauliflower-like carbon material. This mass volume concentration can be, for example, 3 mg / ml, 4 mg / ml, 5 mg / ml or 6 mg / ml.

[0043] In the preparation method of the oxygen reduction electrode of the present invention, in step B, the mass percentage concentration of the Nafion ethanol and water mixed solution is 4-9%, that is, the mass percentage concentration of Nafion in this solution is 4-9%, and it can be, for example, 4%, 5%, 6%, 7%, 8% or 9%.

[0044] In the preparation method of the oxygen reduction electrode of the present invention, in step B, the volume of the uniformly mixed solution dropped onto the pretreated glassy carbon electrode is not clearly defined, as long as it can uniformly cover the surface of the glassy carbon electrode. Those skilled in the art can appropriately determine and select it, and no detailed description will be given here.

[0045] Fourthly, the present invention also relates to a fuel cell comprising the oxygen reduction electrode.

[0046] As described above, due to having various excellent electrochemical properties, the oxygen reduction electrode can be applied to a fuel cell, and thus a fuel cell with excellent performance can be obtained.

[0047] As described above, the present invention provides a non-precious metal doped Myriophyllum-derived carbon-based material with oxygen reduction activity, its preparation method, use and an oxygen reduction electrode comprising it. The non-precious metal doped Myriophyllum-derived carbon-based material has excellent properties, can be used to prepare the oxygen reduction electrode of a fuel cell, and thus can be used in a fuel cell and exhibits good electrochemical properties, having great application potential and industrial value in the field of electrochemistry. Description of the Drawings

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, obtaining other accompanying drawings based on these drawings still belongs to the scope of the present invention.

[0049] Figure 1 It is a scanning electron microscope image (SEM) of the non-precious metal-doped Myriophyllum-derived carbon-based material in Embodiment 1 of the present invention.

[0050] Figure 2 It is a transmission electron microscope image (TEM) of the non-precious metal-doped Myriophyllum-derived carbon-based material in Embodiment 1 of the present invention.

[0051] Figure 3 It is a full-scan XPS image of the non-precious metal-doped Myriophyllum-derived carbon-based material prepared in Embodiment 1 of the present invention.

[0052] Figure 4 It is an XPS high-resolution C1s spectrum of the non-precious metal-doped Myriophyllum-derived carbon-based material prepared in Embodiment 1 of the present invention.

[0053] Figure 5 It is an XPS high-resolution N1s spectrum of the non-precious metal-doped Myriophyllum-derived carbon-based material prepared in Embodiment 1 of the present invention.

[0054] Figure 6 It is an XPS high-resolution Fe2p spectrum of the non-precious metal-doped Myriophyllum-derived carbon-based material in Embodiment 1 of the present invention.

[0055] Figure 7 It is a linear voltammetric scan curve of the oxygen reduction electrode prepared using the non-precious metal-doped Myriophyllum-derived carbon-based material in Embodiment 1 of the present invention.

[0056] Figure 8 It is a CV curve of the oxygen reduction electrode prepared using the non-precious metal-doped Myriophyllum-derived carbon-based material in Embodiment 1 of the present invention, with a scan rate of 5 mv / s.

[0057] Figure 9 It is a stability test diagram of the oxygen reduction electrode prepared using the non-precious metal-doped Myriophyllum-derived carbon-based material in Embodiment 1 of the present invention. Detailed implementation manners

[0058] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0059] Embodiment 1

[0060] S1: Cultivate the aquatic plant Myriophyllum verticillatum in 5 L of water containing 150 mg / L for seven days;

[0061] S2: After washing the hydroponic Myriophyllum verticillatum, put it into an oven and dry it at 80 °C for 24 hours;

[0062] S3: After drying, break the obtained dehydrated plant into powder under the action of a wall breaker;

[0063] S4: Take 200 mg of the above powder and 400 mg of urea and put them into a planetary ball mill, and ball mill at a speed of 500 rpm / min for 12 hours.

[0064] S5: Put the material obtained after the above ball milling into a quartz boat, push it into a tube furnace for heat treatment. Under a nitrogen atmosphere, the heat treatment temperature is 800 °C, the heating rate is 5 °C / min, and pyrolysis is carried out for 2 hours. The obtained black powder is the above-mentioned iron-doped Myriophyllum verticillatum-derived carbon-based material.

[0065] S6: Use the above-obtained iron-doped Myriophyllum verticillatum-derived carbon-based material to prepare an oxygen reduction electrode

[0066] A. Polish the glassy carbon electrode on alumina water slurries with particle sizes of 1 μm, 0.3 μm, and 0.05 μm respectively, then ultrasonically wash it in absolute ethanol and high-purity water (with a resistance of at least 18 MΩ) for 30 seconds, and dry it with argon to obtain a pretreated glassy carbon electrode;

[0067] B. Take the above-mentioned iron-doped Myriophyllum verticillatum-derived carbon-based material and disperse it in a mixed solution of ethanol water and Nafion with a mass percentage concentration of 50%, where the mass percentage concentration of Nafion in this solution is 5.5%, and then ultrasonically disperse it for 60 minutes to obtain a uniformly mixed solution (mass volume concentration of 6 mg / ml); Drop the uniformly mixed solution onto the pretreated glassy carbon electrode and cover it evenly, and dry it at room temperature to obtain an oxygen reduction electrode.

[0068] S7: Use the above-obtained oxygen reduction electrode to conduct an oxygen reduction performance test in a 0.1 mol / L KOH solution.

[0069] As described above, the present invention provides a non-noble metal-doped Myriophyllum verticillatum-derived carbon-based material with oxygen reduction activity, its preparation method, use, and an oxygen reduction electrode containing the same. The non-noble metal-doped Myriophyllum verticillatum-derived carbon-based material has excellent performance, can be used to prepare an oxygen reduction electrode for fuel cells, and thus can be used in fuel cells, and shows good electrochemical performance, having great application potential and industrial value in the field of electrochemistry.

[0070] It should be understood that the use of these embodiments is only for illustrating the present invention rather than intending to limit the protection scope of the present invention. In addition, it should also be understood that after reading the technical content of the present invention, those skilled in the art can make various changes, modifications and / or variations to the present invention, and all these equivalent forms also fall within the protection scope defined by the appended claims of this application.

[0071] The above-disclosed are only the preferred embodiments of the present invention. Certainly, the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A fuel cell, characterized in that: The fuel cell comprises an oxygen reduction electrode comprising a non-noble metal-doped myriophyllum-derived carbon-based material, A non-noble metal-doped myriophyllum-derived carbon-based material having oxygen reduction activity, wherein the preparation method comprises the following steps: S1: Cultivating the biomass Myriophyllum in a water environment containing metal ions; S2: Wash the product in S1 and remove the water; S3: Grinding the dried biomass in S2 into powder; S4: doping the powder in S3 with an external nitrogen source to obtain a metal-nitrogen composite biomass material precursor; S5: heat treating the precursor in S4 in a tube furnace under inert gas protection to obtain a myriophyllum-derived carbon-based material; The metal in the water environment containing metal ion components is one or more of iron, nickel, cobalt, and copper, and the metal ions are derived from water-soluble metal inorganic salts; In step S2, the dehydration comprises one of thermal drying, natural drying and freeze drying; In step S3, the grinding method can be mechanical stirring, ball milling and ordinary mortar grinding; In step S4, the external nitrogen source doping method is ball milling and / or impregnation; In step S4, the mass ratio of the added nitrogen source to the foxtail algae powder is 1:1-4; In step S5, the inert gas includes nitrogen and argon, and the heat treatment temperature is 700°C-1100°C; The method for preparing the oxygen reduction electrode comprises the following steps: A. Grind and polish the glassy carbon electrode in alumina slurry with a particle size of 1-0.05 μm for multiple times, then ultrasonically wash the electrode in anhydrous ethanol and ultrapure water for 20-60 seconds, and blow dry with argon gas to obtain a pretreated glassy carbon electrode; B. Take the non-precious metal-doped foxtail algae-derived carbon-based material in a mixed solution of ethanol, water and Nafion, and then ultrasonically disperse it for 30-60 minutes to obtain a mixed uniform slurry; drop the mixed uniform slurry onto the pretreated glassy carbon electrode and dry it at room temperature to obtain an oxygen reduction electrode.

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