Preparation And Oxygen Reduction Properties Of Platinum-Cobalt Based Ordered Intermetallic Compounds

The oxygen reduction reaction（ORR）is an essential half-reaction in fuel cells.However,the multi-step and slow electron transfer of ORR and low mass transfer efficiency leads to sluggish kinetics,which greatly hinders its practical application.In recent decades,despite ORR catalysts has been developed with high electrocatalytic performance and stability,they have not been mass-produced due to the limitation of material cost and complicated technical process routes.Therefore,the development of novel electrocatalyst for fuel cell cathode is an urgent issue to be addressed.The aim of this paper is to prepare highly active platinum carbon（Pt/C）catalyst and optimized the process parameters by simple synthesis process and materials.In addition,the Pt/C catalysts were doped with transition metal elements cobalt and manganese to enhance the oxygen reduction activity and stability by rationalizing the structure composition,particle size,and electronic structure,thus reducing the amount of precious metal platinum.A water-modified polyol reduction method was utilized to synthetize a high-loaded Pt/C catalyst.The controlled synthesis of a single batch gram-scale highly active Pt/C catalysts was achieved by investigating the effects of key reaction factors,such as reaction steps,solvent ratios,reaction times and carbon support types,and by improving the preparation process（metal loading and solvent amounts）.The catalyst was observed through TEM,revealing PtNPs were highly dispersed on the carbon support.The results showed that the Pt/C catalyst prepared at 90℃for 3 h of reflux reaction and 0.6 volume ratio of ethylene glycol had the highest catalytic performance.The atomically ordered intermetallic compounds（IMCs）of platinum-cobalt were synthesize by seed-mediated growth and heat treatment,which optimization of catalyst surface structure by acid-washing treatment and secondary heat treatment.The results showed that the catalysts prepared at 800℃exhibited excellent catalytic performance with a mass activity of 209.1 A·g^-1.After ADT of membrane electrode,the electrochemical surface area was enhanced by 2.5%,which indicated that PtCo-IMCs exhibited good stability.Based on the research of PtCo-IMCs,doped with a second transition metal element manganese.The electrochemical test results exhibited that the ORR performance of the catalyst(282 A·g^-1)was higher than that of the PtCo-IMCs catalyst(209 A·g^-1)and much higher than the commercial Pt/C catalyst(90A·g^-1)when the atom ratio of cobalt to manganese was 4.8.The maximum power density of the membrane electrode is 1.393 W·cm^-2when the cathode platinum loading is 0.15 mg _Pt·cm^-2,which corresponds to the platinum utilization of 0.143 g _Pt·k W^-1,close to the DOE 2025 target(0.125g _Pt·k W^-1).