Doping Regulation Of Mo₂C And Electrocatalytic Nitrogen Reduction Performance

The industrial nitrogen fixation for the production of ammonia（NH₃）mainly relies on the conventional Haber-Bosch process under conditions with high temperature and pressure.This process requires heavy energy consumption and causes abundant CO₂emissions.The electrocatalytic nitrogen reduction（NRR）has attracted considerable attention as an environmentally friendly strategy for ammonia synthesis at room temperature and pressure.However,the NRR process requires overcoming the high energy barrier to break the N≡N bond,and the strong adsorption of protons at most active sites makes competitive hydrogen evolution reaction（HER）always more dominant than NRR,resulting in poor catalytic activity and low selectivity of NRR.Therefore,the design of ideal electrocatalysts with high catalytic activity and selectivity has become the focus and difficulty of current research.Transition metal carbides（TMCs）with rich d-orbital electronic structures can inject electrons into theπ*orbitals of N₂,thus effectively weakening the N≡N bond and showing adsorption behavior similar to that of noble metal catalysts.Therefore,this paper chooses molybdenum carbide（Mo₂C）electrocatalytic material as the main research object.Through metal and non-metal doping to adjust its electronic structure,improve the adsorption and activation of nitrogen molecules,reduce the reaction energy barrier,so as to improve its NRR electrocatalytic activity and selectivity.Firstly,we prepared the Ni-doping Mo₂C anchored in the graphitized porous carbon to study its NRR catalytic performance.Benefited from the porous structure and graphitization features of the carbon matrix,the catalyst obtains more active sites and higher electrical conductivity.Meanwhile,the doped Ni atom replaces the Mo atom to achieve dual active site construction and optimize the Ni-Mo electronic configuration,which promotes the adsorption and activation of N₂.Moreover,the lowered energy barrier of the NRR process and the suppressed hydrogen adsorption on the active site,all resulted in the high catalytic activity and selectivity of the catalyst.The NH₃ yield was 46.49μg h^-1 mg^-1 and the FE was 29.05%,which were 2-fold and 3.16-fold higher relative to the undoped catalyst,respectively.In addition,the B-doped Mo₂C anchored on nitrogen-doped carbon was investigated.The B element was able to induce the phase transfer from hexagonal Mo₂C to cubic Mo₂C under high-temperature conditions with stronger intrinsic NRR electrocatalytic activity.In addition,B-element doping leads to the d-band center of Mo closer to the Fermi energy level,and its charge transfer with N₂ molecules is further enhanced,which enhances the adsorption and activation of nitrogen.In addition,the adsorption of hydrogen protons on the catalyst surface was effectively suppressed,exhibiting excellent NH₃ yields(52.1μg h^-1 mg^-1)and FE（36.9%）,which were 1.8-fold and 4-fold higher relative to the undoped catalyst,respectively.