Construction Of Transition Metal Phosphides And Their Activity In Hydrogen Evolution Reaction

Currently,traditional energy sources come from fossil fuels,such as coal,oil and natural gas,but they can't meet the social demands with the development of society.The increasing fossil fuel crisis and accompanying environmental pollution are motivating researchers to develop clean energy technologies.Hydrogen,as an ideal energy carrier,is one of the most potential alternatives to fossil fuels owing to its eco-friendly and high energy output.Water electrolysis,due to its simple technology,high product purity,reliable in operation and so on,is an attractive technology to future sustainable hydrogen production.A desired hydrogen evolution reaction?HER?electrocatalyst is essential to decrease the overpotential for highly efficiency.To date,the state-of-the-art electrocatalyst for HER is commercial Pt-based catalysts?Pt/C?.However,its large-scale utilization is seriously constrained by its rarity and high cost.Therefore,searching earth-abundant catalysts with high HER performance and durability is required to satisfy the hydrogen generation for future sustainable hydrogen economy.Hydrogen evolution electrocatalysts are mainly divided into:metal alloy,metal carbides,metal borides,metal nitrides,metal phosphides,metal chalcogenides,and heteroatom-doped carbon nanomaterials.The transition metal phosphides have excellent thermal stability,good electrical conductivity and chemical stability,so they can be used as catalyst for the electrolysis of water to produce hydrogen,and show excellent electrochemical performance.This paper mainly introduces the preparation of diruthenium phosphide nanoparticles and their research in hydrogen evolution reaction,and discusses the activity trend between different crystal phase ruthenium phosphides and how to further improve the hydrogen evolution activity of diruthenium phosphide nanoparticles.The specific research results are as follows:1.Ruthenium and platinum are precious metal elements belonging to the eighth group,but the price of ruthenium is only 1/3 of platinum with the strong stability.In this article,we reported ultrasmall ruthenium phosphide nanoparticles grown on reduced graphene oxide nanosheets?Ru₂P/graphene-20?as a Pt's superior in HER electrocatalysis.This Pt-free catalyst can achieve a current density of 10 m A·cm^-2 at extremely low overpotential of 22 and 13 m V with small Tafel slope of 29 and 56 m V dec^-1 in acidic and alkaline conditions,respectively,all superior to commercial Pt/C.It also exhibits excellent long-term durability and high Faradaic efficiency.Density function theory?DFT?calculation suggests that Ru-Ru-Ru hollow site is the most favourable hydrogen adsorption site,where the Gibbs free energy of hydrogen adsorption reaches a desirable value of 0.058 e V due to partial electron transfer from Ru to underlying sp² carbon when Ru₂P is combined with graphene.Considering the low price?ca.1/3 of Pt?and low loading of Ru,this catalyst holds great promise for practical application.2.We developed a general strategy to fabricate Ru₂P,Ru P,and Ru P₂nanoparticles on graphene,named Ru₂P/graphene-PA,Ru P/graphene-PA,and Ru P₂/graphene-PA,respectively.This approach allows controllable synthesis of various Ru phosphides by simply changing the dosage of phytic acid?PA?as P source while keeping the loading density and nanoparticle dimensions of phosphides at the same level.Electrochemical tests showed that Ru₂P/graphene-PA exhibits the highest intrinsic HER activity,followed by Ru P/graphene-PA and Ru P₂/graphene-PA.Ru₂P/graphene-PA achieves a current density of 10 m A cm^-2 at overpotential of 18 m V in acid solution.Theoretical calculations further revealed that P-deficient Ru₂P has a lower free energy of hydrogen adsorption on the surface than other two P-rich Ru phosphides?Ru P,Ru P₂?,which confirms the excellent intrinsic HER activity of Ru₂P and is consistent with experiment results.3.Based on the electrochemical performance trend of ruthenium phosphide obtained in the previous chapter,we reported Ru₂P nanoparticle decorated P,N co-doped carbon nanofibers on carbon cloth?Ru₂P@PNC/CC-900?as a highly active and durable hierarchical HER electrocatalyst in both acidic and alkaline media.Electrochemical tests show that Ru₂P@PNC/CC-900 has Pt-like HER performance to afford 10 m A cm^-2 HER current density at low overpotential of 15 and 50 m V in acidic and alkaline condition,respectively.DFT calculations suggest that coupling Ru₂P nanoparticles with heteroatom-doped carbon fibers leads to enhanced intrinsic HER performance.4.We rationally designed and developed a novel Mo₂C/Mo P hybrid nanoparticle embedded N,P dual-doped carbon nanofibers on carbon fiber paper?Mo₂C-Mo P NPC/CFP-800?as a highly active hierarchical HER catalyst.Taking advantage of structural and compositional merits,the Mo₂C-Mo P NPC/CFP-800 electrocatalyst shows excellent catalytic activity as well as good durability for HER.Only 85 and 146m V overpotential is needed to drive a HER current density of 10 m A cm^-2 at acidic and alkaline p H,respectively.Remarkably,the catalyst is also able to perform efficient HER even in seawater.In summary,this paper has rationally designed and synthesized transition metal phosphides from structure,phosphorus content and phase types,and explored the internal mechanism of its effect on the catalytic electrolysis of hydrogen evolution reaction.It has provided important practical experience toward the future energy application.