Electrocatalytic Activity Regulation And Mechanism Investigation Of Molybdenum Dioxide For Electrocatalysts Toward Hydrogen Electrode Reaction In Alkaline Media

Alkaline membrane water electrolysis and anion exchange membrane fuel cell can realize the application of inexpensive non-precious metal catalysts,thus reducing the cost of hydrogen energy conversion devices and.However,the hydrogen electrocatalysis reaction（hydrogen evolution reaction and hydroxide reaction）in alkaline media is of 2 to 3 orders of magnitude slower compared to acidic conditions,and the reaction mechanism is not yet clear,the effect of oxophilicy on alkaline hydrogenation reaction is still under debate.Aiming at the above problems,this paper purpose on improving the electrocatalytic activity of the hydrogen electrocatalysis and explore the reaction mechanism of the hydrogen electrode under alkaline conditions.The catalyst designed and prepared is based on MoO₂,a substance with good oxophilicy,which significantly improves the catalytic activity of the hydrogen electrode of the catalyst and establishes the structure-activity relationship to further explore the reaction mechanism of the hydrogen electrocatalysis under alkaline conditions.The main research contents and results of this article are as follows:Ni/MoO₂nanosheet catalysts were prepared by hydrothermal reduction method,and the catalytic activity of hydrogen evolution reaction under alkaline conditions was studied.The results show that the recombination of MoO₂ greatly enhances the catalytic activity of Ni for hydrogen evolution.The NMOU400 requires an overpotential of only 40 m V to achieve a current density of 10 m A cm^-2 in 1.0 M KOH.Combined with the difference in catalytic activity of HER under acidic and alkaline conditions,it was found that MoO₂ promotes the dissociation of water,thereby increasing the reaction activity.Subsequently,the preparation process was optimized to reduce the particle size of the metal Ni and increase the exposure of the Ni/MoO₂ active interface,thereby showed good catalytic activity for hydrogen oxidation.The comparison experiments through the preparation of Pt/C-MoO₂ demonstrated that the bifunctional effect of MoO₂ is the key factor for the improvement of the HOR activity.In order to further improve the catalytic performance of the Ni electrode,the two properties of hydrogen adsorption energy and oxygen affinity were adjusted for the first time.The nitrogen doping and MoO₂ cooperation were used to simultaneously change the hydrogen binding energy and oxophilicity of the Ni electrode.A Ni₃N and MoO₂ composite catalyst was prepared that nitrogen doping regulates the hydrogen adsorption energy of Ni and MoO₂regulates the oxygen affinity.The catalyst exhibits the highest reported HOR exchange currents of 13.22 m A mg _Ni^-1and kinetic current densities of 107.3 m A mg _Ni^-1.The strategy of regulating oxophilicy is further extended to other metals and the composite catalyst of Pd,Ru,Pt,Ir,Rh and MoO₂ was prepared.The analysis of the changes of the catalytic activity of different metal hydroxides with the same oxophilic sites shows that the catalytic activity has been improved by the cooperation of MoO₂,indicating that this strategy of constructing oxygen-promoting sites has good universality.For the first time,it was found that the increase in the catalytic activity of the catalyst for hydrogen oxidation has a certain correlation with the offset of the CO stripping peak,indicating that the oxophilicy is the main reason for the increase in activity,which provides a new experimental proof for the bifunctional theory.In order to reveal the phenomenon that most of the non-precious metal hydrogen evolution catalysts do not have hydroxide activity.Ni,Co,Mo alkoxides were used as precursors to prepare nitrogen,sulfur,phosphide and their MoO₂ complex.By comparing different metal valence states and the effect of MoO₂ on the hydrogen electrode activity of these catalysts,combined with their physical characteristics and CV analysis,it is supposed that the requirement for the catalyst to possess HOR activity is the metals exist in zero valence.This result provides the guidance for the design of non-noble metal catalysts in the future.