Design,Synthesis Of Transition Metal Based OER Catalysts And Related Study Of Their Structure,Performance

Electrocatalytic water splitting to produce highly purified clean hydrogen gas(H2)is one of the most significant methods for alleviating the problems of energy crisis and environmental pollution at present.Oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)are of great significance for water splitting,and principally determine the rate and efficiency of H2 production.Compared with HER,the reaction rate of OER is lower and the reaction energy barrier is larger,because OER involves four-electron transfer process.Therefore,high rate and efficiency of water splitting are highly dependent on efficient and stable OER catalysts.Transition metal-based materials,due to their tunable electronic structure,have been considered as the most potential alternatives to noble metal-based OER catalysts.However,numerous transition metal-based materials are facing some drawbacks in conductivity and active site,which restrict their applications in electrocatalysis.In view of these shortcomings of transition metal-based materials,several facile synthetic strategies were developed to synthesize novel transition metal-based OER catalysts in this dissertation.The specific findings are as follows:The conductivity of traditional cobalt phosphate is not good,and the number of exposed active sites is limited due to its large sizes.Given the problems,we reasonably selected O-phospho-DL-serine as the multifunctional raw material,and after adding Co source,cobalt phosphate nanoparticles decorated with nitrogen doped carbon layer(Co3(PO4)2@N-C)were prepared via solvothermal and high temperature treatment.As-prepared Co3(PO4)2@N-C catalyst exhibited good OER activity and stability in 1 M KOH electrolyte.The onset potential is 1.47 V and Tafel slope is 62 mV dec-1,which is even better than standard IrO2 catalyst.O-phospho-DL-serine worked as sources of phosphorus,carbon and nitrogen at the same time.During the synthetic process,O-phospho-DL-serine was transformed into nitrogen-doped carbon layer,and deposited on the surface of cobalt phosphate nanoparticles to increase the conductivity of the obtained catalyst.Moreover,the size of as-prepared Co3(PO4)2@N-C is about 80 nm,leading to abundant active sites,which could contribute to the excellent performances.This work provides method guidance for facile synthesis of transition metal-based materials/nitrogen-doped carbon composite electrocatalysts.When nanomaterials are loaded onto the conductive substrates,polymer binder is needed,which could suppress the performances of electrocatalysts.To address this problem,a novel example of cobalt phosphide nanoparticles anchored on cobalt foil(CO2P/Co-foil)as a self-supported electrode was prepared by one-step in-situ phosphorization of the pre-oxidized Co foil.The obtained electrode can be directly used as a working electrode in alkaline electrolyte and showed excellent and stable OER performances,achieving current density of 10 mA cm-2 at a low overpotential of 319 mV.Moreover,the integrated electrodes could be used as both the anode and the cathode for practical water splitting,which also exhibited outstanding activities.The Co foil not only worked as Co source to prepare Co2P nanoparticles,but also acted as current collector for active Co2P particles to obtain the self-supported integrated electrode.No polymer binder is needed,leading to a strong interaction between Co2P nanoparticles and conductive Co foil,which results in remarkable catalytic performances.Our method opens a new avenue for large-scale preparation of highly active and self-supported electrodes.Reasonable doping strategy is a useful way to improve the performances of electrocatalysts.Based on the advanced one-step in-situ synthetic method,the iron-nickel alloy(FeNi)foil was selected as the sources of Fe,Ni and conductive supporter.Fe doped Ni3S2 nanosheets array on conductive FeNi foil as a self-supported electrode was successfully prepared.This as-prepared integrate Fe-Ni3S2/FeNi electrode displayed superb activity and stability towards OER in alkaline solution,with a small overpotential of 283 mV at current density of 10 mA cm-2.Combined with DFT theoretical calculation,the results proved that Fe doping could tune the electronic structure of Ni3S2,increase the active sites,and optimize the barrier and rate of O2 evolution.Fe doping as well as the strong interaction of Fe doped Ni3S2 nanosheets and FeNi foil greatly boost the OER performances.