Controlled Synthesis Of New Transition Metal Phosphates And Their Electrocatalytic Hydrogen Production Properties

As energy and environmental issues become increasingly serious,the development of new energy sources that can replace non-renewable fossil energy sources is particularly urgent.Hydrogen energy with many advantages has become one of the hot candidates for the development of next-generation energy.However,based on the existing technology,the production of hydrogen often requires the participation of fossil energy,which does not fundamentally solve the existing development problems.Therefore,the development of new hydrogen production methods has become the research focus of many scientists.The electricity generated from disposable renewable energy(wind,light,water)could produce hydrogen by water splitting,which can achieve no carbon or pollutant emissions in the hydrogen production process.Moreover,the production of hydrogen from sodium borohydride,ammonia borane,formic acid and other hydrogen-containing compounds can also achieve the goal of low pollution and low energy consumption to produce hydrogen.However,though noble metal-based catalysts often show excellent catalytic activity in above-mentioned hydrogen production process,it is difficult to achieve true large-scale commercial hydrogen production because the high cost and scarcity of the noble metalsThe purpose of this paper is to design and synthesize transition metal phosphide catalysts with high efficient,stable and low cost properties.Improving the efficiency of new hydrogen production methods(hydrogen production by electrolytic water and by hydrolysis of sodium borohydride),and preparing clean and high-purity hydrogen is the starting point.An efficient and stable Co,Mo-based transition metal three-dimensional self-assembly catalyst strategy has been developed.We have design,synthesizd and investigated the 3D self-supported CoP/NPC/TF electrodes,interfacial heterojunction catalysts CoP/CoMoP,and Mo-based catalyst MoS2-MoP/NC in hydrogen evolution reaction(HER)in water splitting.In addition,CoP nanowire catalysts can be used to catalyze sodium borohydride for hydrogen production.The main research contents are as follows:A vertically aligned core-shell structure grown on Ti foil with CoP nanoarray as a core and N,P-doped carbon(NPC)as a shell(CoP/NPC/TF)is first reported as an efficient electrocatalyst for HER.Results indicate that CoP/NPC/TF only demands the overpotentials of 91 and 80 mV to drive the current density of 10 mA cm-2 in acidic and alkaline solutions.The electrochemical measurements and theoretical calculations show that the synergy of CoP nanorod core and porous NPC shell enhances HER performance significantly,because the introduction of porous NPC shell not only offers more active sites but also improves the electrical conductivity and durability of the sample in acidic and alkaline solutions.Density functional theory calculation further reveals that all the C atoms between N and P atoms in CoP/NPC are the most efficient active sites,which greatly improve the HER performance.The identification of active species in this work provides an effective strategy to design and synthesize the low-cost,high-efficient,and robust CoP-based electrocatalysts.A heterostructure electrocatalyst on Ni foam with CoP nanowires coupled with the defective CoMoP nanosheets(CoP/CoMoP)is first synthesized via hydrothermal method followed by low-temperature phosphidation.Results indicate that CoP/CoMoP shows extraordinarily efficient HER activity and robust stability,especially,high activity superior to that of commercial Pt/C in alkaline electrolyte,due to the cooperative effect of interfaces between CoP and CoMoP.Density functional theory(DFT)calculations certified that the interface between the CoP and CoMoP can improve the activity of HER,especially in alkaline condition,by facilitating the H2O-dissociation on the CoMoP and H-adsorption on the CoP.Moreover,the CoMoP with P defects can enhance the activity of HER by preventing the active sites of CoMoP and CoP from the blocking of OH*.It is expected that such heterostructure CoP/CoMoP could provide a powerful interface-engineering strategy to design and construct efficient cooperative electrocatalysts for HER.A new strategy is reported to synthesize the N-doped carbon-encapsulated interface construction between MoS2 and MoP,derived from the partial phosphidation of MoS2 by incorporating P source(MoS2-MoP/NC).As a novel interface engineering electrode,MoS2-MoP/NC exhibits not only Pt-like catalytic activity in alkaline electrolyte but robust durability after continuous stability test.Experiment results certify the interface between the MoS2 and MoP can effectively improve the HER activity and the carbon can protect the active materials of MoS2-MoP under durable measurement in alkaline condition.In this work,porous CoP nanowires(NWs)have been successfully prepared via the low-temperature hydrothermal method and the comprehensive experiments validate that the sample is a high efficient bifunctional catalyst for both the reduction of 4-nitrophenol and sodium borohydride hydrolysis.Specifically,the as-prepared porous CoP NWs exhibit more excellent catalytic performance(knor=743 s-1 g-1)than that of other reported catalysts towards reduction of 4-nitrophenol.The catalytic activity of sodium borohydride hydrolysis is also investigated and the CoP NWs show superior hydrogen generation rate(4028 mL min-1 g-1)at 30? for sodium borohydride hydrolysis.Our results indicate that porous CoP nanowires possess a potential application on both the sodium borohydride hydrolysis and reduction of 4-nitrophenol.