Research On Structure Control And Electrocatalytic Performance Of Mo/Fe Compounds

In recent years,clean energies such as solar energy,wind energy and hydrogen energy have attracted growing concerns due to the dual problems of the energy crisis and air pollution caused by the excessive use of fossil fuels.Among them,hydrogen has unparalleled advantages such as high energy density and pollution-free.Electrolytic water hydrogen production is expected to become a sustainable hydrogen evolution method.However,water splitting process is restricted by the high intrinsic activation barriers,the electrolyzer usually operates at a voltage much higher than the theoretical limit voltage（1.23 V）.Using efficient electrocatalysts can effectively improve the sluggish kinetics and decrease the overpotential.This thesis mainly applies to high-temperature carbonization and hydrothermal reaction,synthesizes xTM-Mo₂C@NCF and（Mo,Fe）P₂O₇@NF by metal doping modification and construction of pyrophosphate heterostructures,respectively,the structure and electrochemical properties of the materials were characterized and analyzed.Specific research contents are as follows:（1）The electronic structure of molybdenum carbide is adjusted by coating on carbon substrate and doping transition metals to enhance its conductivity and structural stability.Herein,a series of transition metal modified molybdenum carbides in a nitrogen-doped carbon matrix（xTM-Mo₂C@NCF）are synthesized to maximize exposed active sites.Among them,0.5%Fe-Mo₂C@NCF delivers better hydrogen evolution performance over a wide range of electrolytes.Overpotentials of 65,130 and129 mV at 10 mA cm^-2 and Tafel slopes of 76,109 and 110 mV dec^-1 were obtained in1.0 mol L^-1 KOH,1.0 mol L^-1 phosphate buffer solution and 0.5 mol L^-1 H₂SO₄,respectively.The computational study further demonstrates that the synergistic electronic modulation co-activated by Fe and N dopants in Fe-Mo₂C@NCF can reduce the Gibbs free energy of H adsorption(ΔG_H^*),which contributes to an increased catalytic performance.（2）Mo/Fe bimetallic pyrophosphate was uniformly coated on the surface of nickel foam（NF）by hydrothermal method and low temperature phosphating to obtain（Mo,Fe）P₂O₇@NF electrocatalyst with excellent oxygen evolution activity in alkaline medium.The synergistic effect of bimetallic active centers has greatly increased active sites,the active materials are tightly combined with the three-dimensional conductive substrate to improve the structural stability of the electrocatalyst.Overpotential required for（Mo,Fe）P₂O₇@NF in 1.0 mol L^-1 KOH（purity:85%）to provide high current densities of 100 and 600 mA cm^-2 are 250 and 290 mV,respectively.In addition,the（Mo,Fe）P₂O₇@NF electrocatalyst also exhibits excellent performance in alkaline simulated seawater and 1.0 mol L^-1 KOH（purity:99.99%）electrolytes.