Green Synthesis Of Metal Phosphide-Based Catalysts And Their Performance And Optimization For Water Electrolysis

Hydrogen energy is considered as the cleanest and perfect energy source.Electrochemical water splitting for production of hydrogen is a promising and environmentally friendly technology in the future but its large-scale practical application is mainly limited by high energy consumption.At present,there are two research strategies to lower energy consumption:one is to prepare efficient and low-cost catalysts;The other is to replace the high energy consumption oxygen evolution half reaction（OER）so as to achieve efficient hydrogen production.In terms of catalyst,transition metal phosphides are a kind of catalytic material with high activity,corrosion resistance and low cost,which have gained more and more attention and research.However,they are usually prepared by phosphating of phosphine with highly toxic and flammable generated by the pyrolysis of phosphorous salts.Therefore,it is necessary to optimize the synthesis of transition metal phosphate to promote its practical application.On the other hand,OER is mainly replaced by anodic oxidation or anodic synthesis reaction whose initial potential is required to be lower than the theoretical potential of water electrolysis（1.23V）,thus to reduce the overpotential of the overall reaction.For this regard,efforts are aimed at improving the efficient utilization of anodic reaction,which can realize the purpose of environmental treatment or organic synthesis simultaneously.In this paper,the phytic acid with strong chelation ability with metal are selected as green phosphorus source for synthesis of transition metal phosphides to optimize the traditional preparation method,thus enabling efficient electrocatalytic overall water splitting;In addition,the electrocatalytic anodic oxidation reaction of formaldehyde（FOR）is used to replace sluggish OER to reduce the energy consumption of electrocatalytic overall water splitting for production of hydrogen and realize the pollutants treatment in the water environment.The main research contents of this paper are as follows:（1）On the substrate of stainless steel mesh,with synthetic CoFe LDH by hydrothermal method as precursor and phytic acid as phosphorus source,P-doped CoFe nanoparticles loaded on P-doped carbon sheets compound is synthesized by chelation reaction between CoFe LDH and phytic acid followed by calcination reduction process.The phosphorus element is introduced and meanwhile a few amount of carbon is also introduced.This hierarchical structure composite exhibits excellent bifunctional overall water splitting activity.The overpotential of HER and OER(10 m A cm^-2)in 1 M KOH alkaline electrolyte are 139m V and 281 m V,respectively.To achieve the current density of 10 m A cm^-2,the two electrodes cell voltage is 1.64 V and its stability is much better than that of commercial platinum carbon and ruthenium dioxide.This work provides a method for the synthesis of P-doped three-dimensional transition metal-based nanomaterials and a possibility for the optimization of catalytic properties by structural engineering transformation.（2）On a flexible carbon cloth substrate,a three-dimensional nano-structured transition metal phosphide-based catalyst（Ni Co-Ni Co P@PCT/CC）is synthesized by the chelation reaction between cobalt-nickel bimetallic nanowires precursor and phytic acid followed by subsequent calcination process.Moreover,the reaction process and mechanism are investigated in detail.In addition,the water electrolysis for production of hydrogen is optimized by the efficient coupling of FOR and HER.The as-synthesized Ni Co-Ni Co P@PCT/CC shows many functional catalysis activities.The electrolyzer which is constructed with Ni Co-Ni Co P@PCT/CC as both cathode and anode can achieve the current density of 50 m A cm^-2 in HCHO wastewater with a cell voltage of 1.76 V,which is about 320m V less than that of traditional pure water electrolyzer that needs 2.07 V.At the same time,the hydrogenation reduction reaction of formaldehyde can be carried out in the cathode,which realizes the upgrading and conversion of HCHO and the resources utilization.This work not only provides a way for the safe and controllable synthesis of 3D nano-structured transition metal phosphates using phytic acid as P source and chelation agent,but also proposes a new electrolyzer coupling system for the efficient production of hydrogen energy and the treatment and conversion of environmental pollution.