Preparation Of Oxide-supported Cobalt-based Electrocatalysts And Their Oxygen Reduction Performance

Oxygen reduction reaction（ORR）?is the central reaction of numerous sustainable energy conversion systems such as zinc-air batteries,ZABs.However,cathodic ORR suffers from slow kinetics and high overpotentials,which restrict the practical application of these energy conversion systems.Therefore,designing high-performance catalysts is crucial for accelerating ORR electrocatalysis.Although Pt/C catalysts have excellent performance,they suffer from the disadvantages of high cost and low durability.Carbon-supported non-noble transition metals have catalytic activities comparable to Pt/C,but electrochemical oxidation of carbon supports can lead to loss or aggregation of supported catalysts,thereby reducing the durability and activity of electrocatalysts.In recent years,low-bandgap oxides have received extensive attention due to their excellent electrical conductivity and electrochemical stability,providing a way to address the instability of carbon-supported electrocatalysts.In this paper,combined with the design of oxygen vacancies（OVs）,cobalt（Co）-based electrocatalysts supported by low-bandgap oxides were used to construct three-dimensional ordered macroporous（3DOM）structured ORR electrocatalysts 3DOM Co@WNO and 3DOM Co/NPC@Ti O_2-x,which was subjected to a series of characterization and electrochemical performance tests and applied to primary zinc-air batteries.The research work is as follows:（1）Three-dimensionally ordered macroporous tungsten oxynitride（WNO）loaded Co nanoclusters（3DOM Co@WNO）high-performance ORR catalysts were prepared by pyrolysis of precursor-containing polystyrene（PS）templates.The tungsten oxynitride carrier with oxygen vacancies not only provides high conductivity and stability of the catalyst,but also ensures good dispersion and strong anchoring of the loaded Co clusters,thus achieving high catalytic activity and durability.In 0.1 M KOH,3DOM Co@WNO exhibits excellent ORR performance with a half-wave potential(E_1/2)of 0.85 V（vs.RHE）,which is comparable to Pt/C and has better durability and methanol resistance than Pt/C.Density functional theory（DFT）suggests that the electron transfer occurring between the interfaces of WNO and Co clusters leads to more electron accumulation around the Co sites,promoting the ORR reaction kinetics.In addition,3DOM Co@WNO as a primary ZAB cathode exhibits high power density(185 m W cm^-2)and higher specific capacity(740 Wh kg^-1)than Pt/C at 20 m A cm^-2.（2）High-performance ORR catalysts(3DOM Co/NPC@Ti O_2-x)with Co-based N and P co-doped carbon（Co/NPC）embedded in three-dimensional macroporous structure of oxygen-rich vacancy Ti O₂(Ti O_2-x)were prepared by pyrolysis containing precursor PS templates.The three-dimensional macroporous structure provides high specific surface area,good mass transfer and strong structural stability.The ORR catalytic activity and stability of 3DOM Co/NPC@Ti O_2-xare better than Pt/C in 0.1 M KOH.Density functional theory reveals that the high ORR activity can be attributed to the synergistic effect of N and P co-doping and the presence of Co,which facilitates oxygen adsorption while lowering the reaction energy barrier.The primary ZAB using 3DOM Co/NPC@Ti O_2-xas cathode exhibited higher open-circuit voltage（OCV,1.50 V）and high specific capacity of 820 Wh kg^-1at 20 m A cm^-2discharge.In this paper,two low-bandgap semiconductor carriers with three-dimensional macroporous structures,WNO and Ti O_2-x,loaded with Co-based ORR electrocatalysts were synthesized.The combination of experiments and theoretical calculations shows that the synergistic optimization strategy of intrinsic activity and mass transfer capacity is beneficial to improve the ORR performance,which provides a reference for the design and synthesis of efficient and stable ORR electrocatalysts.