Study On The Preparation Of Transition Metal Phosphides With Water-splitting Performances

Hydrogen energy plays a significant role in building a green,low-carbon,economy,and diversified energy supply system.And the green hydrogen produced by the electrolysis of water with zero carbon emission,so it has developed rapidly in recent years.The electrocatalytic water splitting involves two half-reactions of oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）.However,generally,the overpotentials of HER/OER are very high.In recent years,to reduce the overpotential of electrodes and enhance the efficiency of hydrogen production,transition metal phosphides with low prices,excellent catalytic activity and low overpotentials have attracted great attention.For example,transitional metal phosphides such as Fe P,Co P,Ni P and Mn P have been proved to show high HER/OER electrocatalytic activity.However,the defects of single-component transition metal phosphides catalysts,such as small number of active sites,insufficient performance,and poor stability,limit their industrial application greatly.Based on this,this research utilizes synergistic effects to explore the syntheses of multielement transition metal phosphide catalysts on various substrates to improve the defects of single-component transition metal catalysts.the specific researches are as follows:（1）Preparation and Screening of Single/dual Transition Metal Phosphides Codoped Porous Carbon CompositesN-P codoped porous carbon has become an ideal non-noble metal bifunctional catalyst in recent years due to its high specific area and excellent bifunctional catalytic activity.In this work,firstly,series of single metal phosphide catalysts（Fe P@N-PPCs）were synthesized using N-P codoped porous carbon（N-PPC）as a carrier through adjusting ratios,hydrothermal times,and phosphating.The HER/OER properties of catalysts were evaluated by the electrochemical methods.After obtaining the best HER/OER performance conditions,Co and Ni elements were added into Fe P@N-PPC to synthesize binary transition metal phosphide catalysts.Then,the prepared catalysts were characterized by SEM,TEM,XPS,BET,and XRD.Electrochemical dates showed that in alkaline solutions,the OER overpotentials of the Fe Ni P@N-PPC and FeCoP@N-PPC at 10 m A cm^-2 were only 231 and 237 m V,which are much lower than those 319 and 512 m V of Fe P@N-PPC2 and the commercial noble metal Ir O₂ catalysts.Meanwhile,the HER overpotentials at 10 m A cm^-2 of FeCoP@N-PPC and Fe Ni P@N-PPC were only 276 m V and 312 m V.And there was no significant change in the OER/HER polarization curve of the catalyst before and after 2000 cycles of CV.Therefore,FeCoP@N-PPC and Fe Ni P@N-PPC have high OER/HER bifunctional activities and stability,mainly benefiting from synergistic effects,strong interaction between transition metal phosphides and N-PPC carriers,and the high conductivity of N-PPC carriers.（2）Preparation and Electrocatalytic Performances of Multicomponent transition metal phosphides Codoped Porous Carbon CompositesConsidering the superior HER/OER performances of binary transition metal phosphides to those of single compoment,ternary/quaternary/pentagonal transition metal phosphides were loaded on to the surface of N-PPC carrier in this work.And their OER/HER electrocatalytic performances were evaluated under alkaline conditions through electrochemical methods.Text results showed that the OER overpotentials of Fe Co Mn P@N-PPC,Fe Co Mn Ni P@N-PPC,Fe Co Ni Cu P@N-PPC,Fe Co Mn Cu P@N-PPC,Fe Co Mn Ni Cu P@N-PPC and commercial catalysts at 10 m A cm^-2 were 264,244,432,177,386,and 521 m V,respectively.Among them,Fe Co Mn Cu P@N-PPC possessed high OER performance(Tafel slope of 138 m V dec^-1).Meanwhile,the HER overpotentials at 10 m A cm^-2 of Fe Co Mn P@N-PPC,Fe Co Mn Ni P@N-PPC,Fe Co Ni Cu P@N-PPC,Fe Co Mn Cu P@N-PPC and Fe Co Mn Ni Cu P@N-PPC were 264,244,432,251 and 386 m V,respectively.Impressively,Fe Co Mn Cu P@N-PPC also exhibited high HER catalytic activity(Tafel slope of 98 m V dec^-1).Those results demonstrated that the OER/HER performances of multicomponent transition metal phosphide catalysts were much higher than those of single/binary transition metal phosphide catalysts,indicating that multi-compositing is an effective way to improve OER/HER performances of transition metal phosphides.Among them,Fe Co Mn Cu P composite materials promising a potential for water-splitting application.（3）Syntheses and OER/HER electrocatalytic performances of Fe Co Mn Cu P/nickel foam（NF）catalystOwing to the high conductivity and HER/OER electrocatalytic activities,NF is often used as a carrier to prepare high-performance self-supporting OER/HER electrocatalysts.In this chapter,Fe Co Mn Cu P/NFs at different phosphating temperatures were prepared by hydrothermal and phosphating reactions,and their OER/HER performances were evaluated through electrochemical methods in alkaline solutions.Results showed that in 1.0 M KOH,the overpotentials of Fe Co Mn Cu P/NF2catalyst were only 88 and 425 m V at 10 and 100 m A cm^-2.And under the same conditions,the HER overpotentials of this catalyst were only 147 and 336 m V at 10 and100 m A cm^-2.At the same time,overall water splitting system Fe Co Mn Cu P/NF||Fe Co Mn Cu P/NF worked stably for 48 hours in 1.0 M KOH at a potential range of 1.56V to 1.61 V at 10 m A cm^-2,indicating an excellent stability.And Fe Co Mn Cu P/NF promising a good industrial application prospect.