Preparation Of Cobalt And Nickel-based Chalcogenides Catalysts For Electrochemical Water Splitting

The development of green and sustainable clean energy is the key to solve the seriously environmental pollution and the depletion of fossil fuels.It is an attractive approach to convert clean energy sources,such as wind and solar,which are time and space unevenly distributed,into sustainable,high-energy density fuels or chemicals.Hydrogen prepared by water splitting technology has the advantages of high purity,high energy density and no pollution in combustion,concidering as an ideal carrier for clean energy.However,the water splitting technology for hydrogen production still suffers from the high reaction potential and low energy conversion efficiency.The development of well-defined catalyst to reduce the reaction energy barrier and accelerate the reaction rate is the key to the rapid development of current technology.Precious metal catalysts（IrO₂,RuO₂,Pt）are relatively ideal catalysts at present,but their high price limits their large-scale application in the future.The development of non-precious metal-based catalyst is the focus of the research and the key to promote the industrial production of hydrogen from water splitting.Especially,the fundermental understanding of electrochemical activity related to electrocatalysts structure will appealing whereas still challenging.Here,the facilitate synthesis of transition metal chalcogenides,the employment of as-prepared catalysts for electrocatalytic water splitting,and the investigation of the relationship between structure and electrochemical activity were demonstrated.The mainly research contents are as follows:（1）N and Ce co-doped cobalt sulfide（N,Ce-CoS₂）was prepared by a two-step synthesis method.N,Ce-CoS₂ showed excellent catalytic performance of oxygen evolution reaction（OER）with overpotential of 190 mV(j=10 mA cm^-2)and long stability（120 h）.The structure characterization revealed the reason for the high activity of the catalyst.The complementary electronegativity property of N and Ce elements enable the efficient protection of catalyst surface against oxidation,thus exbiting long-term stability under harsh alkaline testing conditions.The doping of the two elements is helpful for the formation of high oxidation sites in the catalyst,which reduces the adsorption energy of intermediates and products.（2）Self-supporting nickel sulfide with different crystal phases（Ni₃S₂ and NiS₂）were synthesized by direct sulfiding of nickel foam.The self-supported Ni₃S₂ exhibited excellent electrochemical activity in both hydrogen evolution reaction（HER）and OER catalysis,with overpotential of 123 mV and 245 mV(j=10 mA cm^-2),respectively.In overall water splitting,the current density of 10 mA cm^-2 could be reached at a voltage of only 1.61 V.Through structural characterization and theoretical calculation,the relationship between electrochemical activity and different crystal phases of nickel sulfide was elucidated.Compared with NiS₂,the d-band center of Ni atom in Ni₃S₂ is closer to Fermi level,which can better balance proton adsorption and hydrogen desorption in HER.Combined with Bader electron and X-ray photoelectron spectroscopy（XPS）analysis,Ni₃S₂ contains high oxidationstate Ni³⁺,which can be regarded as the active site of OER.（3）P-doped nickel selenide（P-NiSe₂）was synthesized by selenization with the assistance of NaH₂PO₂.The over-potential of P-Ni Se₂ in HER and OER was 71 mV and 270 mV(j=10 mA cm^-2),respectively.In overall water splitting,the current density of 10 mA cm^-2 can be reached at only 1.58 V.Structural characterization and theoretical studies show that P doping makes the d-band center of Ni atom closer to the Fermi level,which promotes proton adsorption and hydrogen desorption.P doping increased the valence state of Ni site.Compared with pure NiSe₂,P doping reduces the reaction energy barrier,thus shows excellent activity in OER.