Preparation Of Carbon Wood Fiber-based Transition Metal Phosphide And Their Properties For The Urea Electrooxidation

With the increasing population of the world,human energy demand will surpass crude oil reserves within a few decades,requiring an urgent search for a sustainable and clean alternative to fossil energy.As an energy-dense,carbon-neutral fuel,hydrogen energy is considered an ideal substitute to fossil fuel.At present,urea electrolysis has been considered as an effective way to produce hydrogen from urea-rich wastewater.The theoretical voltage of urea electrolysis is only 0.37 V vs.RHE,much lower than the typical theoretical potential required for water electrolysis(1.23 V vs.RHE),which can significantly improve the efficiency of hydrogen production.Transition metal phosphide has attracted wide attention due to its similarity in structure with hydrogenase,abundant reserves and low cost.However,it still has issues with metal particles easy to aggregate,poor conductivity and low durability.Therefore,it is essential to effectively improve the catalytic performance of transition metal phosphide through catalyst regulation strategy for the preparation of efficient urea electrooxidation reaction(UOR)catalyst.This paper develops a series of catalysts with high efficiency urea electrooxidation performance based on transition metal phosphide,and effectively improves the performance by designing and regulating the micro-morphology and structure of the catalyst.The synergies of morphology,element doping and conductive matrix on UOR catalyzed reaction of transition metal phosphide were studied.The research work in this paper provides a new idea for the design and preparation of high efficiency urea assisted hydrogen production catalyst and the high value-added utilization of wood residues.The specific research content is as follows:(1)Taking green and renewable WF as matrix,Ni(OH)2NiOOH/WF nanosheet arrays were grown on WF by hydrothermal method,and then Ni2P/PCWF electrocatalysts supported by wood carbon fiber with uniform Ni2P nanoparticles were prepared through simultaneous phosphorization and carbonization.The synergistic effect between Ni2P and PCWF in the UOR process is enhanced through electronic structure regulation and interface regulation,which improves the UOR performance of the catalyst.The electrochemical test results show that Ni2P/PCWF can reach the current density of 50 mA cm-2 with only 1.34 V(vs.RHE)in 1.0 M KOH and 0.5 M urea electrolyte,and shows excellent stability.In a urea assisted electrolytic hydrogen production device,Ni2P/PCWF as anode and Pt/C as cathode achieve a current density of 50 mA cm-2.The battery voltage is only 1.49 V,which is 260 mV lower than the potential required for water electrolysis.(2)Based on the morphology control strategy,a ZIF-67-derived P-doped wood carbon fiber supported P,N co-doped carbon coated CoP nanoparticle composite electrocatalyst(CoP@PNC/PCWF)was prepared by synchronous carbonization phosphating method using ZIF-67 as template.Its unique coating structure can give the electrocatalyst good conductivity and structural stability.At the same time,P-doped carbon can induce more defects in wood carbon fiber and further regulate the electronic structure of CoP@PNC interface.The results of electrochemical tests showed that CoP@PNC/PCWF showed excellent UOR catalytic performance in 1.0 M KOH and 0.5 M urea electrolyte,and reached 50 mA cm-2 current density of only 1.32 V(vs.RHE).In addition,CoP@PNC/PCWF was used as anode to form a two-electrode system with commercial Pt/C,which also showed excellent urea-assisted hydrogen production.