Transition Iron-Based Catalysts Coupling Low-Carbon Molecules Electrooxidative Reaction And Hydrogen Evolution Reaction

The increasing global energy demand and the imminent threat of climate change due to the combustion of fossil fuels have motivated considerable efforts to develop technologies to generate,convert and store renewable energy.One promising way is to use the renewable energy electricity（e.g.electricity generated by soalr or wind）for water or seawater electrolysis to produce green hydrogen.Hydrogen evolution reaction（HER）at cathode and oxygen evolution reaction（OER）at anode are two important half reaction in conventional water electrolysis.However,the intrinsically sluggish kinetics of oxygen evolution reaction is often considered an obstacle that limits the overal energy conversion efficiency of water electrolysis.Although,some novel OER catalysts with the outstanding activities have been developed,it is still impossible to achieve low-energy to achieve low-energy hydrogen production.Besed on this,it is a new feasible strategy to replace OER with thermodynamically favorable biomass oxidation reaction to improve ovreal energy conversion efficiency of water electrolysis.In this paper,transition metal carbide and transition metal oxide catalyst were designed by reasonable composition design and structure construction,and their structural morphology,electrochemical properties and catalytic mechanism were studied.（1）A trimetallic carbide（Co₃Fe₃W₆C）,derived from one-pot systhesis,could act as a rubust electrocatalyst for formaldehyde upgrading reaction（FUR）to produce formate at a high faradic efficiency（>98%）,without any production of CO₂ or O₂.Compared to OER,the input voltages of Co₃Fe₃W₆C-catalyzed FUR are 150 and 120 m V lower to achieve current densities of 10 and 50 m A cm^-2,respectively,thereby facilitating a significant boost in the energy efficiency of water elecrtrolysis.Besed on theoretical calculations evidence discussed above,A site in A₆W₆C occupancies by Co and Fe,which could optimized the electronic structure of catalyst to improve electron transfer capability and FUR activity.（2）The bifunctional nickel foam self-supproted nickel ferrite catalyst was sysnthesized by two steps of hydrothermal method and calcination method,which could couple HER with selective methanol oxidation reaction（SMOR）in water or seawater electrolysis.In two-electrodes system,Ni Fe₂O₄/NF||Ni Fe₂O₄/NF catalyzed HER-SMOR system produces remarkably high current densiy(>800 m A cm^-2)with high Faradaic efficiencies（FE）at both electrodes（>96%for HER and>95%for SMOR to formate）.Besides,Ni Fe₂O₄/NF||Ni Fe₂O₄/NF catalyzed HER-SMOR system are sufficiently robust in seawater electrolysis,showing no sign of deactivation or chlorine oxidation reactions over 6 h of continuous operation at a high current density of 700 m A cm^-2.DFT calulations reveal that SMOR proceeds via a CO-free pathway,with Ni and Fe as the active sites for methanol and water activation,respectively.Aiming at the scientific problem that the efficiency of hydrogen production in alkaline electrolyzed water is often limited by the thermodynamically sluggish oxygen evolution reaction,this work proposes a new technical route that using transition metal iron-based catalysts to catalyze the low-carbon molecular formaldehyde and methanol oxidation reaction to replace the oxygen evolution reaction.This strategy can achieve the coupled production of hydrogen（H₂）and value-added anodic product formate（HCOOK）,which provide a new method to solve the inherent engineering problems about hydrogen production by water/seawater electrolysis.