Application Of Graphite-Based Hybrid Materials In Oxygen Electrode Reaction

Electrochemical energy conversion and storage technologies such as fuel cells and metal-air batteries have been widely used.Oxygen reduction（ORR）and oxygen evolution（OER）are the key reactions.However,the kinetics of ORR and OER are slow,requiring the use of highly active and stable catalysts to speed up the reaction and reduce overpotentials.Current commercial catalysts consist of precious metals such as platinum and rhodium,which are expensive and susceptible to poisoning,hindering their use in electrochemical energy conversion and storage technologies.Transition metals and their oxides are promising alternatives to these precious metals.Therefore,in this paper,the transition metal active sites are loaded onto the graphite-based materials by different methods,and these catalytic materials are used for the oxygen electrode reaction.The details are as follows:1.Composite catalyst of binary Ni2FeOx anchored on modified graphite for electrocatalytic oxygen evolution reactionDevelopment of earth-abundant electrocatalysts for the OER is highly desirable.Herein,a binary nickel-iron oxide is supported on the surface of sulfonated-graphite（Ni₂FeO_x@-G-Ph-SN）,and it demonstrates superior electrochemical OER activity(only 265 mV overpotential at 10 mA cm^-2)and outstanding stability in 1.0 M KOH.2.Single-sitecopper-nitrogenco-dopedgraphenecatalystfor electrocatalytic oxygen reductionA single-site Cu-and N-codoped graphene material was prepared by a simple thermal decomposition process.The catalyst exhibits prominent ORR performance in alkaline media,including a positive onset potential（～0.94 V vs RHE）and half-wave potential（0.84 V vs RHE）,a low Tafel slope of 48.0 mV dec^-1,remarkable catalytic stability,and strong tolerant to methanol.The single-site Cu-N-C might be the active site toward efficient ORR.3.Bifunctional single-site iron-based catalyst for oxygen electrode reactionsA single-site iron-and nitrogen-codoped graphene catalyst with high content of iron（up to 1.5 wt%）by thermal decomposition process.The single-site iron-based catalyst on glassy carbon electrodes displays low overpotential（194 mV and 275 mV）reported at 10 mA cm^-22 in 1.0 M KOH and 0.1 M KOH solutions for OER,respectively.In addition,the single-site iron-based composite electrocatalyst exhibits a high half-wave potential of 0.90 V vs RHE for ORR,and a combined ORR and OER potential gap of 0.605 V.Structural characterization and theoretical calculations demonstrate that the efficient active sites for OER and ORR should be FeN₄-moiety embedded into the graphene,on which the overpotential-determining step is the O-O coupling step.