Desigin Of A Highly Active Oxygen Reduction Electrocatalyst Based On The Regulation Of Transition Metal And Heteroatom Doping

The oxygen reduction reaction（ORR）is the main reaction that occurs at the air cathode of a zinc（Zn）-air battery.The ORR reaction process heavily relies on platinum group noble metal electrocatalysts.The scarcity and exorbitant price of platinum group noble metal electrocatalysts greatly impede their large-scale commercialization.Therefore,the development of low-cost,high-efficiency non-precious metal electrocatalysts is of great significance.We takes transition metal as the research object,optimizes electrochemical performance through heteroatom doping.We adjusts the formation conditions to control the morphology and composition of the electrocatalyst to obtain superior electrocatalytic activity.Various experimental methods are used to explore the relationship between the active components of the electrocatalyst and the composition of the catalyst.We further explored the application of the synthesized electrocatalyst in zinc-air batteries.The main research contents are as follows:（1）A facile molten salt assisted two-step pyrolysis strategy to construct carbon nanosheets matrix with the uniformly dispersed Fe₃N/Fe nanoparticles and abundant nitrogen-coordinated Fe single atom moieties(Fe@Fe _SA-N-C).Thermal exfoliation and etching effect of molten salt contribute to the formation of carbon nanosheets with high porosity,large surface area and abundant uniformly immobilized active sites.X-ray absorption fine spectroscopy,wavelet transform（WT）plot and X-ray photoelectron spectroscopy indicate the generation of Fe（mainly Fe₃N/Fe）and Fe _SA-N-C moieties,which account for the catalytic activity for ORR.Further study on modulating the crystal structure and composition of Fe₃N/Fe nanoparticles reveals that proper chemical atmosphere of Fe in Fe₃N/Fe notably optimizes the ORR activity.Consequently,the presence of abundant Fe _SA-N-C moieties,and potential synergies of Fe₃N/Fe nanoparticles and carbon shells,markedly promote the reaction kinetics.In addition,a rechargeable Zn-air battery device constructed by Fe@Fe _SA-N-C-900possesses remarkably stable performance with a small voltage gap without obvious voltage loss after 500 hours of operation.（2）A convenient and effective strategy to synthesis Co metal and Mn O immobilized on carbon nanotubes（Mn O/Co-CNTs）vis strong metal-support interaction（SMSI）.The CNTs support anchored abundant Mn O/Co nanoparticles（NPs）in a small size of～2 nm,when the strong interaction between them suppressed the homogeneous nucleation of Mn O/Co during high temperature sintering.Thus,enormous well-dispersed catalytic active sites are produced on the conductive CNTs.Together with the boosted charge transfer between Mn O/Co and support,the catalytic activity of Mn O/Co-CNTs is eventually significantly promoted.The catalyst shows an efficient oxygen reduction reaction（ORR）,oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）in alkaline solution.Furthermore,SMSI alleviate the agglomeration of NPs and secure the active sites during electrochemical reactions,which account for the enhanced catalytic durability for ORR,OER and HER.In consequence,the Mn O/Co-CNTs catalyst shows excellent performance for rechargeable Zn-air battery,and can be utilized to catalyze overall water splitting to produce hydrogen and oxygen.This work manifests a promising approach for optimizing the catalytic performance of the NPs.（3）An excellent non-noble metal oxygen electrocatalyst called Mn-Nx@C.The catalyst is a very thin nanometer made of high-density Mn-Nx active sites and rich defect-rich carbon materials with pyridine N.This special structure effectively avoids the corrosion of Mn-Nx active sites in acid and alkaline media.The oxygen electrocatalyst formed by high-temperature carbonization has a high density of active sites and good conductivity.The mechanism of ORR/OER performance enhancement is revealed,and the application of ORR/OER dual-function electrocatalysts in Zn-air batteries is explored.The results show that the electrocatalyst exhibits good ORR catalytic activity under the combined action of defective vacant Mn-Nx active sites and two-dimensional nanomaterials.