Electrocatalytic Nitrogen Reduction Performance Study Of W₁₈O₄₉-based Catalysts

Electrocatalytic nitrogen reduction reaction（NRR）for ammonia synthesis can effectively avoid the disadvantages of traditional Haber-Bosch method,and is considered as a potential alternative method.However,the NH₃ yield and faraday efficiency（FE）of electrocatalytic NRR are too low,and the development is restricted.The search for high activity,high stability and excellent selective electrocatalysts has become the research focus in this field.Owing to their easy preparation,low price,and unique electronic structure,transition metal oxides are widely used in the field of NRR.Among them,W₁₈O₄₉ has attracted much attention.On the one hand,W₁₈O₄₉ with abundant oxygen vacancies can effectively facilitate the adsorption and activation of N₂ by donating adsorbed electrons of oxygen vacancies to the anti-bonding orbital of N₂.On the other hand,it has weak binding ability with H atom,which could inhibit the hydrogen evolution reaction.However,the electrocatalytic NRR activity of W₁₈O₄₉ is restricted by less active sites and poor conductivity.In this paper,in order to improve the electrocatalytic NRR performance of W₁₈O₄₉,the oxygen vacancy was generated by the unequal doping of Cu⁺,which was further combined with reduced graphene oxide（RGO）to improve the conductivity,and the mechanism of electrocatalytic NRR was explored.Oxygen-rich Cu⁺doped W₁₈O₄₉ was prepared by the solvothermal method.The introduction of unequal Cu⁺in W₁₈O₄₉ made W_17.5O₄₉-Cu_0.5 obtain more oxygen vacancies and promoted the activation of N₂.In the doping range（0.1-1.0）,W_17.5O₄₉-Cu_0.5 showed the smallest charge transfer resistance and the largest electrochemical active area,thus obtaining the best ammonia production activity(5.13μg h^-1 mg_cat^-1,16.58%),It was found that oxygen vacancies were the main active sites for electrocatalytic NRR by XPS analysis,thermogravimetric analysis,and ammonia yield test analysis after reduction of oxygen vacancies（H₂O₂ oxidation and oxygen high-temperature calcination）.Due to its excellent electronic conductivity,good electrochemical stability,and high surface area,RGO is considered to be one of the composite materials for improving catalytic performance.In order to further improve the problem of W₁₈O₄₉ for poor conductivity and accelerate electron transfer in NRR process,RGO-W_17.5O₄₉-Cu_0.5 catalyst was prepared via solvothermal method.Furthermore,to explore the impact of RGO,the structure,morphology,ammonia synthesis performance,and electrochemical property of the catalyst were analyzed.Among them,3%RGO-W_17.5O₄₉-Cu_0.5 exhibited the highest NH₃ yield(11.41μg h^-1 mg_cat^-1),which was 2.22 times that of W_17.5O₄₉-Cu_0.5(5.13μg h^-1 mg_cat^-1).