Study On The Performance Of Fe-Based Catalysts With Doping For Seawater Electrolysis At Large-Current-Density

The rapid consumption of traditional fossil fuels accelerates the global environmental and energy crisis,and it is imperative to seek environmentally friendly and alternative energy sources.Hydrogen is the most promising energy carrier to replace fossil fuel due to its green and high energy density.In many kinds of hydrogen production technology,water electrolysis as a pollution-free and efficient hydrogen production method has attracted more and more attention.Seawater electrolysis is more suitable for industrial large-scale hydrogen production than freshwater electrolysis because of the abundance of seawater in nature.However,the complex composition of seawater can cause severe corrosion of the electrode and other adverse reactions,thus reducing the efficiency of hydrogen production.Therefore,it is urgent to develop efficient and stable electrocatalysts for efficient seawater decomposition.In this paper,Fe-based catalysts with doping were successfully prepared by one-step hydrothermal method,high temperature gas phase phosphating and molten salt method,which showed excellent catalytic activity and stability in electrolytic seawater hydrogen production reaction.The main contents are as follows:（1）Here,Ru,Ni‐doped Fe₂O₃with a lily shaped morphology was synthesized on iron foam（Ru Ni‐Fe₂O₃/IF）via a hydrothermal process.The prepared Ru Ni‐Fe₂O₃/IF catalyst shows excellent overall water/seawater splitting performance thanks to Ru and Ni bimetallic doping.In 1.0 M KOH（1.0 M KOH seawater）solution,Ru Ni‐Fe₂O₃/IF can be used as a self-assembled two-electrode electrolytic system with a voltage of only1.66（1.73 V）to achieve a current density of 100 m A cm^-2,which is significantly better than the commercial precious metals.In addition,the electrodes show remarkable long‐term durability,maintaining current densities exceeding 100 m A cm^-2for more than 100h in the seawater system.This work provides an efficient,economical method to synthesize self‐standing bifunctional electrodes for large-current-density alkaline seawater.（2）The Ru-doped Fe P₄ nanosheets（Ru-Fe P₄/IF）grown on iron foam are successfully constructed.By combining the thermodynamic favorable hydrazide oxidation reaction（Hz OR）with seawater system,chlorine evolution reaction（Cl ER）can be effectively avoided,so as to achieve hydrogen production from seawater without chlorine.Benefiting from trace Ru doping tuning the size and chemisorption of Fe P₄,the as-prepared Ru-Fe P₄/IF can requires a voltage of 0.90 V to reach 1000 m A cm^-2with outstanding long-term stability and 100%Faradaic efficiency when Ru-Fe P₄/IF is assembled in a two-electrode cell for overall hydrazine splitting（OHz S）.Density functional theory（DFT）calculations show that Ru-doped modulates electronic structure to optimize adsorption free energy of H^*(ΔG_H*)and accelerate the*N₂ to N₂dehydrogenation kinetics for HER.This work provides a good foundation for the rational application of seawater resources and the degradation of industrial wastewater.（3）Oxygen-vacancy enriched Co,P double doped Fe₃O₄ was prepared by molten salt mediated oxidation and low temperature phosphorylation on iron foam.The doping of P atom promotes the conversion of Fe₂O₃ to Fe₃O₄phase.During the OER process,the surface of the catalyst is reconstructed,Fe₃O₄is converted to Fe OOH phase with active site.The doping of Co atoms allows this transformation to be completed at a lower voltage,promoting the kinetics of the reaction.The doping of atoms and the structure of vacancy change the electronic structure of Co,P-Fe₃O₄@IF catalyst,exposing more active sites.Thanks to the above advantages,the as-fabricated Co,P-Fe₃O₄@IF can display the outstanding bifunctional electrocatalytic activity in alkaline seawater（1.0 M KOH seawater）,requiring overpotentials of 261 and 370 m V to achieve 500 m A cm^-2current densities for HER and OER.For overall seawater splitting,Co,P-Fe₃O₄@IF catalyst needs 1.68 V to drive 500 m A cm^-2 at simulated industrial conditions（60℃and6.0 M KOH seawater）.This work provides a simple and feasible strategy for the realization of industrial high current(>500 m A cm^-2)in seawater.