Design And Application Of Cobalt-based Spinel Oxygen Catalyst

The increasing demands of energy and global warming have accelerated the exploration of clean,green and sustainable new energy sources,Rechargeable Zn–air batteries and microbial fuel cells regarded as the most potential new green energy devices in terms of their energy storage capabilities,eco-friendly,low cost,and safe.ORR（oxygen reduction reaction）and OER（oxygen evolution）are key processes in zinc–air batteries and microbial fuel cells,but the slow electron transfer process further hinders their commercial application.Therefore,the design and development of highly active and low–cost oxygen catalysts are crucial for the development of high–efficiency energy conversion systems.Cobalt–based spinel is considered as a potential substitute for noble metal oxygen catalysts because of its stable structure,easy availability,and certain oxygen catalytic properties.However,the general spinel oxide as electrocatalysis cannot meet the actual requirement due to their poor electrical conductivity and low activity density,the structure of cobalt-based spinel needs to be further regulated.In this paper,a bifunctional catalyst with high catalytic activity was designed by tuning the electronic structure of cobalt-based spinel octahedral sites and oxygen sites.The main contents of this paper are as follows:（1）A compound catalyst is synthesized with nitrogen–doped hollow carbon spheres as substrates and Zn_xCo_3–xO₄（0≤x≤1）as active components by hard template method and chemical deposition.Nitrogen doped hollow carbon spheres（NHCS）effectively enhance the electrical conductivity of spinel and provide a large specific surface area for the growth and dispersion of highly catalytically active spinel nanoparticles,which is conducive to the rapid charge transfer.the optimized Zn_0.6Co_2.4O₄/NHCS exhibits excellent oxygen catalytic activity.The assembled rechargeable Zn–air battery affords a high–power density(136 m W cm^–2)and excellent cycle stability of over 120 h at 5 m A cm^–2.In application of cathode in MFC device,the maximum power density is 512 m W m^–2.（2）Treatment of ZnCo₂O₄ with NaBH₄ solution to generate oxygen vacancies,followed by filling of the oxygen vacancies with fluoride ions,which regulates O 2p centers for activating lattice oxygen and reducing reaction energy barrier.Moreover,F ion can stabilize catalysts against accelerated bulk oxygen migration and the formation of excessive oxygen vacancies by precisely tuning the coordinated environment of lattice oxygen.This electrocatalyst exhibits the ultralow overpotential of 350 m V at 10 m A cm^–2 in alkaline medium.The assembled Zn–air batter based on Zn Co₂O_4–xF_x/CNTs achieves a stable charge–discharge for 300 h.