The Preparation And Electrochemical Performance Of Nickel Based Fluoride And Phosphide Catalysts

Recent years have witnessed a significant increase in the ever-growing fossil energy consumption and environmental concerns,thus compelled humans to search for more sustainable,renewable and clean energy sources.Hydrogen is considered by researchers as one of the most ideal energy carriers and clean fuels to replace fossil energy because of its high energy storage density and renewable.Among many hydrogen production methods,hydrogen production by water electrolysis is widely regarded as an effective and sustainable technology to produce high-purity hydrogen.Water electrolysis mainly includes two half reactions:cathodic hydrogen evolution reaction（HER）and anodic oxidation evolution reaction（OER）.The theoretical potential of hydrogen production from traditional electrolytic water is 1.23 V.However,because the oxygen evolution reaction involves the four-electron transfer process（4OH^-→2H₂O+O₂+4e^-）,the kinetics is slow and the energy consumption is large,which indirectly leads to the slow hydrogen evolution reaction,and the actual voltage required for the whole electrolytic water reaction is much higher than its theoretical value.Therefore,the main purpose is to prepare transition metal catalysts with high activity,strong stability and low price for hydrogen evolution reaction and reducing the total energy consumption of water electrolysis by urea oxidation reaction（UOR）with relatively low theoretical potential（0.37 V vs.RHE）instead of OER,so as to reduce the overpotential and speed up the reaction.The main contents of this paper are as follows:（1）A novel NiF₃-Ni₂P heterostructure with abundant heterogeneous interfaces in-situ grown on carbon cloth（NiF₃/Ni₂P@CC-2）was controllable synthesized by hydrothermal and subsequent successive fluorination-phosphorization method.Benefiting from the synergistic effect between NiF₃ and Ni₂P,large amounts of high valent Ni³⁺ions,mesoporous diffusion channel and superior hydrophilic surface,the heterojunction composite exhibits excellent catalytic towards UOR and HER,merely1.36 V vs.RHE and 121 mV is required to achieve the current density of±10 mA cm^-2.Moreover,it can continuous operation at±10 mA cm^-2 for 10 h with no significant decrease of catalytic activity,indicating the high stability of the catalyst.When NiF₃/Ni₂P@CC-2 is used as the anode and cathode to assemble the urea electrolyzer,the urea overall oxidation only needs 1.54 V to achieve a current density of 10 mA cm^-2,which is significantly lower than overall water splitting（1.58 V）,proves that urea electrolysis has obvious thermodynamic and kinetic preponderance over water electrolysis.（2）The partially amorphous fluorine-decorated nickel iron layered double hydroxides（NiFe-F）is constructed via two-step hydrothermal and low-temperature fluoridation method.Our study found that HF acid etching of NiFe LDH precursor resulted in the partially amorphous feature and abundant oxygen vacancies,providing rich reaction sites and enhancing electrical conductivity as well as improving the performance of UOR.Simultaneously,the formation of ionic metal-F bond makes it easier to form high valence metal oxyhydroxide active sites.The electrochemical results showed that the as-prepared NiFe-F-4 electrode has excellent catalytic UOR performance with a superb mass activity of 1290 mA mg^-1 at 1.6 V vs.RHE.Moreover,NiFe-F-4 casts remarkable long-term durability for 40 h without performance decay.This work holds great promise to develop advanced electrocatalysts for pollution treatment of urea-rich wastewater and energy-saving H₂ production.