Research On The Design And Performance Of Non-noble Metal Carbon-based Oxygen Reduction/evolution Bifunctional Catalyst

Renewable energy such as solar energy,wind energy,and tidal energy have discontinuous and unstable characteristics,and large-scale energy storage equipment is needed.Zinc-air flow battery is one of the most ideal energy storage technologies with high safety,low cost and long life.However,the reaction kinetics of the oxygen reduction and oxygen evolution of the positive electrode of zinc-air flow battery are slow,resulting in low energy conversion efficiency of the battery,and it is urgent to develop a cheap and efficient bifunctional catalyst.Carbon-based catalysts have the advantages of excellent electrical conductivity,adjustable functions,and low production costs.However,carbon-based catalysts have low active site density and the catalytic activity still needs to be improved.This paper focuses on the research of non-metallic and non-precious metal carbon-based bifunctional catalysts,designing and synthesizing highly efficient metal catalytic active centers,and increasing the density of active sites.The main research results are as follows:1.Developed a host-guest strategy to prepare nitrogen and boron co-doped carbon materials.Using the host-guest synthesis strategy,the boron-containing guest molecule(phenylboronic acid)is encapsulated in the pore cage of the zeolite imidazole framework ZIF-8.By adjusting the ratio of phenylboronic acid,the optimal ratio of hetero atoms to carbon atoms can be optimized.A series of non-metallic carbon-based bifunctional catalysts(B-N-C)were prepared by pyrolysis and used to catalyze oxygen reduction/evolution reactions.The results show that the ratio of boron atoms in phenylboronic acid to zinc atoms in ZIF-8 is 30%.After two-step carbonization and the cracking temperature is 1100?,the prepared catalyst(30%B-N-C-1100)has the best catalytic performance of oxygen reduction(E1/2=0.82 V vs.RHE)and catalytic performance of oxygen evolution(Ej=10mA/cm2=1.77 V vs.RHE).2.In order to further improve the oxygen reduction and oxygen evolution activity of the catalyst,on the basis of the above,the ion exchange was used to replace zinc in the ZIF-8 skeleton with iron,and we studied the effect of phenylboronic acid molecules on the structure and content of iron species.Studies have shown that when boron atoms in phenylboronic acid account for 20%of the zinc atoms in ZIF-8,50 mg of ferric chloride hexahydrate is added,metal atom agglomeration can be avoided,making the iron loading in the catalyst up to 5.49 wt%,increasing the active site density.At the same time,the hollow structure enhances mass transfer and improves the utilization rate of the active center.Therefore,the prepared catalyst has high-efficiency catalytic performance.The half-wave potential of the catalytic oxygen reduction reaction is 0.89 V(vs.RHE),and the current of 10 mA cm-2 produced by the catalytic oxygen evolution reaction requires only an overpotential of 0.55V.3.Further increase of single atom iron content.Explore the critical points of the dispersion and reunion of metal atoms,and explore the interaction between guest molecules and metal atoms.The results show that phenylboronic acid molecules can interact with iron ions and prevent iron agglomeration during calcination.When the content of phenylboronic acid is 20%and 110 mg of ferric chloride hexahydrate is added,the metal atoms are still in a highly dispersed state,and there is no phenomenon of agglomeration caused by metal migration.The content of single atom iron can reach 8.65 wt%.