Preparation And Preparation Of La_1-xSr_xCoO_3- Perovskite And Ultra-thin Nickel-iron Sulfide Nanosheets Rich In Oxygen Defects Research On Electrocatalytic Performance

Electrochemical water splitting is one of the eco-friendly and sustainable ways to produce hydrogen energy with high purity,which is considered as the potential candidate for the future energy supply.The overall water splitting process involves two half reactions:the anodic oxygen evolution reaction(OER)and the cathodic hydrogen evolution reaction(HER).Currently,noble metal-based materials,such as IrO2 and Pt,are considered as the state-of-the-art OER and HER catalysts,respectively.However,their widespread applications have been severely hindered by their high cost and scarcity.Therefore,it is highly attractive to develop efficient earthabundant OER and HER catalysts as alternatives to noble metal-based catalysts.Transition-metal-based catalysts have been considered as a family of promising materials to replace precious metal as the next-generation electrocatalysts,attributed to their cost-effectiveness,good stability and high activity nature.Herein,we fabricate the oxygen vacancies rich La1-xSrxCoO3-? perovskites and the nickel iron sulfide ultrathin nanosheets for OER and HER,respectively.A series of characterization and electrochemical tests were carried out,and the following results are obtained:1.We successfully created abundant oxygen vacancies(OVs)in LaCoO3 perovskite through the combination of element doping with plasma treatment.The concentration of OVs in La1-xSrxCoO3-? perovskites were examined by X-ray photoelectron spectroscopy(XPS)and oxygen temperature-programmed desorption(O2-TPD)measurements.The sample of Sr-0.3 exhibited higher OVs concentrations than the other Sr-doping La1-xSrxCoO3-? perovskites.The concentration of OVs was further improved by Ar plasma treatment.The electrocatalytic activities of different samples were evaluated in 1 M KOH electrolyte.The Sr-0.3-p sample was the best performance catalyst,required an overpotential of 326 mV for achieving 10 mA cm-2 with a Tafel slope of 70.8 mV/dec.The result showed that the abundant OVs in LaCoO3 perovskite were responsible for the high OER activity.The electrochemically measurements results show that the electrochemically active surface areas of Sr-0.3-p sample is eight times of that of Sr-0 sample,and the Sr-0.3-p catalyst has a superior intrinsic activity of active sites.In addition,Sr-0.3-p exhibited an excellent stability,it can remains almost unchanged at a currelt density of 10 mA cm-2 for 15 h,and after long-term cycling for 1000 cycles,the polarization curves of Sr-0.3-p with negligible change compared with the original one.2.The bulk nickel iron layered double hydroxides(N.iFe LDH)was synthesized by one step hydrothermal method,and the NiFe LDH ultrathin nanosheets were obtained by the exfoliation of bulk NiFe LDH.Then we prepared the nickel iron sulfide ultrathin nanosheets(NiFeS-NS)via the sulfidation of its NiFe LDH ultrathin nanosheets precursor,which were supported on carbon cloth.NiFeS-NS were an efficient electrocatalyst for HER over a wide pH range(pH=0-14).It only required an overpotentials of 85,273 and185 mV to reach a current density of 10 mA cm'2 with Tafel slopes of 73.1,115.6 and 165.3 mV/dec in 0.5 M 1H2S04,1.00M KOH and 0.5 M PBS,respectively.The electrochemically active surface areas of NiFeS-NS is 103.75 cm-2ECSA which is higher than that of the corresponding bulk nickel iron sulfide(69.5 cm-2ECSA),indicating that more active sites exist in NiFeS-NS.Furthermore,the active sites in NiFeS-NS own higher intrinsic activity.