Preparation And Properties Investigation Of Ruthenium-nickel Based Nano-electrocatalyst For Water Splitting

The energy and environmental problems caused by the large-scale use of fossil fuels are becoming more and more serious.The sustainable hydrogen production by electrocatalytic water splitting is currently one of the most effective solutions,which is divided into two half reactions——the oxygen evolution reaction（OER）and the hydrogen evolution reaction（HER）.However,these reactions with slow kinetics and high overpotential usually need to be carried out in the presence of efficient electrocatalysts to overcome the energy barrier.At present,the biggest obstacle of electrocatalytic water splitting is the activity and stability of anode electrocatalyst.As platinum group metal,ruthenium has excellent OER activity and relatively low price,which is expected to replace the current commercial platinum group OER electrocatalyst.Nickel foam has unique porous structure and excellent electrical conductivity,when it is used as the base material,the activity of the catalyst can be significantly improved.In this thesis,a series of ruthenium-nickel-based electrocatalysts based on foamed nickel are prepared by solvothermal method,electrodeposition method and heat treatment,then their physicochemical properties and electrocatalytic performance were studied.The main works are as follows:（1）Preparation,characterization and testing of RuO₂-Ni₃S₂/NF-30 ultra-thin nanosheet arrays:First of all,the Ni₃S₂/NF ultra-thin nanosheet arrays based on nickel foam were prepared by the solvothermal method.After that,a trace amount of RuO₂ was electrodeposited on it by cyclic voltammetry,and finally the RuO₂-Ni₃S₂/NF was obtained.Compared with the Ni₃S₂/NF precursor,the electrocatalytic activity of RuO₂-Ni₃S₂/NF was significantly improved.At a current density of10 m A cm^-2 in 1 M KOH,it requires overpotentials of only 88 m V and 252 m V for HER and OER respectively,and has a small Tafel slope(99.3 m V dec^-1 and 70.8 m V dec^-1 for HER and OER,respectively).In addition,the effect of RuO₂ content on the electrocatalytic performance of the catalyst were studied,and the results showed that the electrocatalyst prepared by electrodeposition of 30 cycles cyclic voltammetry has best electrocatalytic performance.The main reasons for the good activity of RuO₂-Ni₃S₂/NF-30 are as follows:Firstly,the ultra-thin nanosheet array of the RuO₂-Ni₃S₂/NF-30 enables the catalyst to have a larger electrochemical surface area and expose more active sites.Secondly,the synergistic effect among RuO₂,Ni₃S₂ and NF changes the electronic structure of the material,optimizes the adsorption free energy of the reaction intermediates.Thirdly,the nickel foam substrate has good electrical conductivity and three-dimensional network structure,which improve the electrical conductivity and mass transfer efficiency of the RuO₂-Ni₃S₂/NF-30.（2）Preparation,characterization and testing of RuNiO_x/NF:The ruthenium-nickel-based oxide（RuNiO_x/NF）with nanoporous structure was prepared by hydrothermal and heat treatment.The results of physical characterization and electrochemical performance test showed that RuNiO_x/NF had excellent electrocatalytic performance for water splitting.The current density of10 m A cm^-2 could be obtained in 1 M KOH with overpotential of 42.3 m V（HER）and 212 m V（OER）,and the Tafel slope was extremely low(HER and OER were 37.4 m V dec^-1 and 67.3 m V dec^-1,respectively).In addition,the chronopotentiometry test showed that RuNiO_x/NF had excellent stability.The main reasons for the high activity of RuNiO_x/NF are as follows:Firstly,the nanoporous structure increases the electrochemical surface area and expose more active sites.Secondly,the nanoporous structure has abundant mass transfer channels,which are conducive to material transport and desorption of bubbles.Thirdly,the high temperature annealing improves the adhesion between porous structure and nickel foam,and enhances the stability of the catalyst.Fourthly,different components of RuNiO_x/NF have synergistic effect,which optimizes the adsorption free energy of active sites.There are 29 figures,4 tables and 114 references in this thesis.