Study On Surface/Interface Electronic States Regulation And Electrocatalytic Properties Of Transition Metal Compounds

With the continuous progress of human society,the consumption of non-renewable energy such as fossil fuels is increasingly aggravated,which brings about the problem of the gradual depletion of resources and continuous environmental pollution.Therefore,it is urgent to develop efficient、environmentally friendly and low-cost clean energy.The technology of generating clean energy hydrogen by electrolysis of water has attracted extensive attention from scientists at home and abroad,among them,oxygen evolution reaction（OER）is a research hotspot,which plays an important role in electrochemical decomposition of water.However,due to the complex four-electron transfer process and the involvement of multiple reaction intermediates,the overpotential of OER is too high and the kinetics is slow.Therefore,it is necessary to develop OER catalysts with low cost、good catalytic performance and environmental friendliness to reduce the overpotential and accelerate the reaction.Heterogeneous catalytic reactions usually occur at the surface and interface of the catalyst.Regulation and design of electronic states at the surface and interface will help to improve the catalytic performance of the catalyst.In this study,we mainly focus on the regulation of electronic states at the surface and interface of transition metal compounds,and reasonably optimize the electronic states of transition metal atoms at the atomic scale by means of in-situ growth,plasma treatment,ion exchange and acid etching:In this paper,amorphous NiCo₂（OH）X hollow nanospheres have been grown in situ on MXene for the first time by using Pearson’s hard and soft acid base principle and coordination etching process.The strong coupling between NiCo₂（OH）X and MXene results in the change of the spin states of transition metal ions and the obvious3d electron delocalization.Plasma treatment further tuned and optimized the electron orbital configuration of the transition metal to the best state.The intermediate spin state（t2g⁵eg¹）of transition metal ions and the low local electrons（i.e.the existence of delocalization state）are favorable for electron transfer,which makes the participating species more likely to adsorb to the active site of Co/Ni,thus improving the OER activity.Ti3C2Tx Mxene@NiCo₂（OH）X-P has the best OER activity with an overpotential of 268 m V after 15 minutes of plasma treatment.The structure、electron spin and delocalized electron cloud density of the composites are discussed and analyzed in detail.This work provides a new idea for rational regulation of electron spin state and delocalized electron density.Co-NiO was synthesized by ion exchange method and annealing process,and the proportion of Ni³⁺in Co-NiO was adjusted by solution etching process（ammonium cerium nitrate）.The Ni³⁺-rich surface was conducive to the formation of the active site NiOOH,thus effectively improving the OER performance.When etched with ammonium cerium nitrate for 60 minutes,the optimal OER performance is 253 m V at current density of 10 m A/cm².This work provides an idea for improving OER performance by properly setting doping and adjusting transition metal valence state.