Synthesis Of Ni And Co-based Nanomateirals And Their Electrocatalytic Performance

Electrochemical energy storage and conversion are regarded as one of ideal pathways to realize the utilization of the clean energy,such as electrocatalytic water splitting,hydrogen fuel batteries and metal-air batteries.The electrocatalytic water splitting involves hydrogen evolution reaction and oxygen evolution reaction,while metal-air batteries include oxygen reduction reaction and oxygen evolution reaction.However,the sluggish reaction kinetics can lead to the high overpotential,thus preparing electrocatalysts to lower the reaction barrier is highly required.The high cost,low abundance and poor stability of traditional noble-metal based catalysts limit the large-scale application.Therefore,it’s urgent to develop efficient,cost-effective and stable electrocatalysts.Herein,based on nickel-based and cobalt-based transition metal compounds,electrochemical performances of catalysts are enhanced by constructing multi-component heterostructures,regulating the spin-state of metal active sites and loading noble metal single-atom,which is beneficial to modify the electronic structure and coordination environments,increase active sites and enhance the adsorption of reaction intermediates,thus improving the electrocatalytic performance.Firstly,amorphous Ni O nanosheets coupled with Ni and Mo O₃ nanoparticles（Mo O₃/Ni-Ni O）are fabricated via two-step electrodeposition strategy.The as-synthesized Mo O₃/Ni-Ni O composite exhibits excellent electrocatalytic HER/OER performance,affording low overpotentials of 62 m V at 10 m A cm^-2 and347 m V at 100 m A cm^-2for catalyzing the hydrogen and the oxygen evolution reaction（HER/OER）,respectively.DFT theoretical results demonstrated that the generated Ni-Ni O and Mo O₃-Ni O heterostructures optimize the hydrogen adsorption and significantly reduce the energetic barrier for HER and OER,respectively.This work provides experimental guidance for the rational design hybrid nanomaterials for diverse catalytic processes.Secondly,we synthesized Mo-doped amorphous cobalt sulfides with different Mo doping content by hydrothermal method,and the influence of Mo doping on the spin state of Co²⁺and ORR activity of amorphous Co S was investigated.Experimental results demonstrate that the e_g filling of Co²⁺in amorphous Co S nanosheets can be regulated by Mo doping.It is attributed to the contraction of Co-S bond after Mo doping,leading to a broader energy gap between t_2g and e_g due to the enhanced crystal field,and resulting in the spin-state transition from HS(t_2g⁵e_g²)and LS(t_2g⁶e_g¹)consequently.DFT calculations reveal that Mo doping can optimize the adsorption of oxygen intermediates on Co S,accelerating ORR reaction kinetics.The fabricated zinc-air battery with Mo-doped amorphous Co S as cathode shows small charge/discharge performance and good cycle stability.Finally,Ni_0.85Se and Ni Se nanosheets supported platinum single-atom catalysts were synthesized by the electrostatic adsorption method,and the effects of different substrates on the electronic structure and coordination environment of Pt single atoms were studied.Experimental results display strong electronic metal-support interaction of Pt and nickel selenide,and the oxidation state of Pt single atom in Pt-Ni_0.85Se is higher than that in Pt-Ni Se.Electrochemical tests suggest Pt-Ni_0.85Se exhibits excellent HER activity with an overpotential of 45 m V at the current density of 10 m A cm^-2,comparable to that of commercial Pt/C and higher than that of Pt-Ni Se.In addition,Pt-Ni_0.85Se could be operated for 120 h under the current density of 10 m A cm^-2 without evident decay,demonstrating excellent stability.