Preparation And Electrocatalytic Water Splitting Performance Of Transition Metal Sulfides And Phosphides

The energy that today’s society mainly relies on is fossil energy represented by petroleum,which has caused serious resource shortages due to its non-renewability;in addition,the consumption of fossil energy has brought serious environmental pollution and greenhouse effect.In order to meet the current needs of people’s lives,the consumption of fossil raw materials is gradually increasing,and environmental pollution is becoming more and more serious.People urgently need to find a green,clean and renewable resource.As the best clean energy for the development of human society in the future,H₂ is considered to be the best alternative to fossil fuels due to its clean and efficient characteristics,and will become the most potential energy carrier in the future.At present,the electrocatalysts used for hydrogen production in the industry are the noble metals Pt/C and Ru O₂,but their large-scale use is limited due to their high price and low reserves.Therefore,the development and design of high-efficiency,stable and low-cost electrocatalysts has become a hot research topic.Based on the above,this thesis takes transition metal（mainly Ni,Co）sulfide phosphides as the research object,and obtains highly efficient and stable electrocatalyst materials by doping with non-metallic elements and constructing heterostructures.The electrochemical performance of electrodes in different electrolytes was studied by electrochemical workstation.The particular works were summarized as follows:1.Using the reducibility of sodium borohydride to construct a cobalt precursor on graphene nanosheets,an N-doped cobalt disulfide catalyst（N-CoS₂/G）supported on the graphene nanosheets was synthesized through one-step low-temperature vulcanization.Using thiourea as the N source and S source ensures that the metal elements in the precursor Co-precursor/G form uniformly distributed small-sized nanoparticles after vulcanization, thereby generating more active sites.At the same time,the introduction of N atoms can not only promote the adsorption of reaction intermediates,but also promote the stable connection of CoS₂ nanoparticles and graphene nanosheets to improve electron transfer. More importantly,the N-CoS₂/G catalyst has excellent catalytic activity at a current density of 10 m A cm^-2.The electrocatalyst with the highest activity was selected by adjusting the amount of thiourea used.In the alkaline electrolyte,only 260 m V and 109 m V of low overpotential are required for the OER process and the HER process to achieve a current density of 10 m A cm^-2.In addition,after assembling the electrode into an N-CoS₂/G|| N-CoS₂/G electrolytic cell,the overpotential of 1.58 V is required at a current density of 10 m A cm^-2,which greatly enhances the overall water decomposition performance of the catalyst.It is also superior to the reported Co-based bifunctional catalysts and other non-noble metal catalysts.2.A simple hydrothermal method was used to synthesize the precursor of MoS₂ nanosheets on a hydrophilic carbon cloth,and then the transition metal elements（Co,Ni,Fe,Cu）were introduced by dipping,and then a one-step vulcanization method was used to construct a precursor of MoS₂ nanosheets.Series of heterostructures of transition bimetallic sulfides.By hybridizing transition metal sulfides（CoS₂,Ni S₂,Fe S₂ and Cu S）with highly active MoS₂ nanosheets,unique interfacial interactions and synergistic catalysis are achieved,so that all catalysts achieve greatly improved bifunctional activity.The experimental results show that for the HER reaction,the current density of CoS₂@MoS₂/CC to reach 10 m A cm^-2 only requires 31 m V;for the OER reaction,the Ni S₂@MoS₂/CC heterostructure shows the best activity,only 225 m V can reach 10 m A cm^-2.After the two catalysts are assembled into an electrolytic cell,the electrolytic cell requires only 1.58 V at a current density of 10 m A cm^-2, which is less than most reported non-noble metal catalysts.3.A simple one-step coordinated phosphating/sulfidation reaction was used to synthesize a dianion-modified nickel-cobalt metal catalyst.By optimizing the P/S ratio,the S₂-Ni Co P_x/NF catalyst with the best catalytic performance was obtained.It has high-efficiency catalytic activity for the HER reaction in an alkaline medium.At a current density of 50 m A cm^-2,the overpotential only requires 144 m V,which is much lower than the original Co Ni P_x/NF catalyst.In addition,S₂-Ni Co P_x/NF also shows faster reaction kinetics and ultra-long stability,which is manifested in that the Tafel slope is only 66 m V dec^-1 and can be maintained at a current density of 10 m A cm^-2 Stability above 12 h.