Preparation Of Co-based Electrocatalysts For Oxygen Reduction Reaction

The slow oxygen reduction reaction（ORR）is a key electrode reaction in fuel cells and metal-air batteries,and high-efficiency electrocatalysts are required to accelerate the reaction,thereby enhancing cell performance.In this paper,based on Co-based catalyst,it is closely combined with other metal components to construct a composite Co-based catalyst.The structure-activity relationship of composite Co-based catalysts was studied through modern characterization techniques and electrochemical testing techniques,and the ORR catalytic performance of this type of catalysts is continuously optimized.The main contents of this work are as follows:1.A series of Co-Co Ti O₃/Ti O₂ catalysts were obtained by loading Co active components onto the surface of Ti O₂ nanoparticles by impregnation method.Various characterization results show that the Co-Co Ti O₃composite nanoparticles are tightly bound to the Ti O₂ support.The electrocatalytic performance of this series of catalysts was evaluated.Among them,the catalyst with 15 mmol Co loading exhibited the best ORR performance:the half-wave potential was 0.84 V（vs.RHE,the same below）,the onset potential was 0.92 V,and the limiting current was 4 m A/cm².The ORR catalytic performance of this catalyst is already close to 20 wt%Pt/C;and the Tafel slope is 52.5 m V/dec,which is less than 83.9 m V/dec for 20wt%Pt/C.It is applied to high temperature proton exchange membrane fuel cells.As the temperature increases,the battery performance gradually improves.When the cell temperature was 180°C and the onset potential was 0.72 V,the highest power density achievable was 9 m W/cm² when the current density reached 40 m A/cm².2.On the basis of the first part,the Ag-Co bimetallic ORR catalyst:Co-Ag-Ti O₂ was successfully prepared by one-pot water bath method.Among them,the 30%Ag-Co-Ti O₂-700℃catalyst exhibits the best ORR performance,which is attributed to the favorable charge transfer efficiency brought by the appropriate content of Ag.Based on this advantage,the catalyst has a lower Tafel slope and a higher electrochemically active area,thereby exhibiting higher ORR activity and selectivity for the four-electron pathway:an onset potential of 0.88 V and a half-wave potential of 0.78 V,the limiting current density is 5.46 m A/cm²;the electron transfer number is about 3.9.3.A series of Co-Sm-g-C₃N₄ catalysts were prepared by low temperature heat treatment as g-C₃N₄ carrier.Structural characterization confirmed that this is a single-atom catalyst composed of Co and Sm bimetallic single atoms.It was used to catalyze ORR and oxygen evolution reaction（OER）and zinc-air batteries.Among them,5%Sm/Co-g-C₃N₄-140exhibited the most optimized ORR and ORR catalytic performance.The difference between the OER potential at 10 m A/cm² and the ORR half-wave potential(E_OER-ORR value)is only 0.78 V,showing high bifunctional electrocatalytic performance.In a zinc-air battery,the bimetallic single-atom catalyst enables the battery to exhibit a high specific capacity of773.26 m Ah/g_Zn and a specific energy of 974.31 Wh/kg.The excellent ORR/OER bifunctional catalytic performance is attributed to the strong interaction between Co and Sm single atoms.