Preparation Of Nano Cobalt Trioxide Based Electrode Catalyst And Its Performance In Direct Methanol Fuel Cell

Direct methanol fuel cell（DMFC）has the unique advantages of simple structure and direct use of methanol aqueous solution or steam methanol as fuel without reforming hydrogen to generate electricity,has been widely used in communications,electric vehicles and portable smart devices.The monomer of DMFC is composed of three parts:membrane electrode,cathode and anode of battery,among which the bipolar catalyst of battery is the key to restrict its further development.At present,noble metal platinum（Pt）-based materials are the most widely used catalysts for DMFC,and this type of catalyst has good catalysis for both the methanol oxidation reaction（MOR）at the anode and the oxygen reduction reaction（ORR）at the cathode.Effect.However,during the reaction process,with the permeation and precipitation of methanol,the by-products(such as COH_ads,HCHO_ads,and CO_ads,etc.)generated by insufficient methanol oxidation will directly reduce the effective area of the electrocatalytic reaction of Pt nanocatalysts until the catalyst is poisoned and deactivated,which seriously affects the catalytic quality and service life of methanol fuel cells.In addition,the small reserves of precious metal Pt and the high price and cost limit the wide application and in-depth development of platinum-based nanoelectrocatalytic materials in the field of DMFC,which is not conducive to commercial large-scale use.In this paper,the non noble metal oxide cobalt trioxide based material is selected as the cathode catalyst of direct methanol fuel cell,and further modified by introducing carbon and nitrogen elements.It has good catalytic effect,and has the advantages of rich raw material reserves,low price,easy preparation,rich synthetic routes,green,environmental protection and no pollution in the preparation process.It has important research value and application prospect.In this paper,the composition,morphology and structure of the prepared materials were studied in detail,and the electrochemical properties of the catalytic materials were further studied.The specific research contents and conclusions are as follows:（1）Spherical,hexahedral and rod-shaped Co₃O₄were prepared by chemical precipitation and thermal decomposition with cobalt nitrate hexahydrate as cobalt source,ammonia bicarbonate as precipitant and polyethylene glycol（PEG20000）as surfactant.The average particle size was 8.54 nm;Compared with commercial Pt/C（20%）,the initial current density of Co₃O₄is 0.0373 m A/cm²less than that of Pt/C（20%）,but the current density attenuation of the two materials in 1 mol/L（KOH+CH₃OH）electrolyte solution is 0.0441 m A/cm²and 0.0686 m A/cm²respectively,indicating that Co₃O₄material has better methanol resistance than commercial Pt/C（20%）.Compared with Co₃O₄and commercial Pt/C（20%）,the ultimate current density is 0.0285 m A/cm²and m A/cm²respectively,The methanol resistance of Co₃O₄material is higher than that of Pt/C（20%）,but it is slightly insufficient in catalytic activity,and the stability needs to be further improved.（2）Mesoporous carbon supported Co₃O₄composite catalyst was prepared by impregnation method with the improved synthetic amorphous mesoporous carbon as carbon carrier,cobalt nitrate hexahydrate as cobalt source and ammonia bicarbonate as precipitant according to the ratio of n（NH₄HCO₃）:n（Co₃O₄）=2.1:1.Compared with commercial vulcan-72 carbon black and glucose,it was found that the specific surface area of Co₃O₄/mesoporous carbon was much higher than that of Co₃O₄/vulcan-72 carbon black and Co₃O₄/glucose carbon,The specific surface area of the three materials is compared:Co₃O₄/C（mesoporous carbon）（977.33 m²/g）>Co₃O₄/C（vulcan-72carbon black）（115.21 m²/g）>Co₃O₄/C（glucose）（34.97 m²/g）.The high specific surface area of the modified amorphous mesoporous carbon is more conducive to the attachment of catalytic active substances and improve the active effective area.In the test of I-T chronoamperometric current,with 1 mol/L（KOH+CH₃OH）solution,the attenuation order of current density of Co₃O₄/C,Co₃O₄and Pt/C（20%）is:Pt/C（20%）（0.0686 m A/cm²）>Co₃O₄（0.0441 m A/cm²）>Co₃O₄/C（0.0171 m A/cm²）.Co₃O₄/C catalyst shows obvious stability and good methanol resistance.Due to the addition of carbon material,the carbon skeleton of Co₃O₄strengthens the transmission of oxygen,The rate of oxidor reaction is increased,so that the limit current is 0.0285 m A/cm²to 0.0798 m A/cm²respectively.The change of overpotential Co₃O₄/C(34.54 m V dec^-1)is significantly less than that of commercial Pt/C（20%）(42.03 m V dec^-1),indicating that Co₃O₄/C material has lower energy consumption in the process of oxygen reduction reaction than commercial Pt/C（20%）material,and the reaction can be started quickly.（3）Co₃O₄/N-C composite catalyst was prepared by calcination and carbonization in a high-temperature tubular furnace with ionic liquid 1-ethyl-3-methyl-dicyandiamide as the precursor of carbon source and nitrogen source,nano cobalt tetroxide as the active material,non-ionic polymer PEG 20000 as the surfactant and MCM-41 molecular sieve as the template.The specific surface area is 421.13 m²/g,and the introduction of nitrogen increases the local charge density of mesoporous carbon.The ORR peak of Co₃O₄/N-C composite catalyst is 0.0361 m A/cm²higher than that of Co₃O₄/C.in terms of methanol resistance,the current density of Co₃O₄/N-C composite catalyst decreases to m A/cm²after 400 s,while Co₃O₄The current density attenuation of Co₃O₄/C and Pt/C（20%）are 0.0441 m A/cm²,0.0173 m A/cm²and 0.0686 m A/cm²respectively.The order of attenuation from large to small is:Pt/C（20%）>Co₃O₄>Co₃O₄/C>Co₃O₄/N-C;The Tafel slopes of Co₃O₄/N-C,Co₃O₄/C,Co₃O₄and Pt/C（20%）are 19.38 m V dec^-1,34.54 m V dec^-1,17.56 m V dec^-1and 42.03m V dec^-1respectively.The change of overpotential Co₃O₄/N-C is significantly less than that of commercial Pt/C（20%）and Co₃O₄/C materials.It can be seen that Co₃O₄/N-C composite catalyst has certain catalytic performance and low reaction energy consumption compared with Pt/C（20%）,Co₃O₄and Co₃O₄/C,Better stability.