Synthesis Of Selenide/carbon Composite And Study On The Electrocatalytic Water Splitting For Hydrogen Evolution Performance

The increase of the energy demand,the rapid consumption of non-renewable fossil fuels and their associated environmental pollution issues have attracted attention.Hydrogen(H2)as an energy carrier,it owns high energy density and can release heat through direct combustion,also can produce clean power by fuel cell,which is regarded as a promising energy.Hydrogen evolution reaction(HER)as the half of the water splitting in the cathode reaction,is regarded as one of the means to produce high purity hydrogen.For water splitting to produce hydrogen,the most practical electrocatalyst is precious metals(Pt)based materials.But the precious metals are restricted to have the large-scale development by some disadvantages that the low storage capacity and high cost.Therefore,it’s very important to look for high efficiency,low cost and stable non-noble metal catalysts for HER materials.This paper takes transition metal selenide-base as the research object,which compounds conductive basement,heterojunction and heteroatom doping methods to improve the HER activity of transition metal selenide material.The specific research contents are as follows:In alkaline,neutral and acid electrolytes,Ni0.85Se/rGO has a smaller overpotential at the current density of 10 mA·cm-2 and a smaller Tafel slope.In addition,NiSe-Ni3Se2/rGO material was prepared by a hydrothermal method as the HER catalyst.In addition to rGO for the enhanced electrical conductivity,NiSe-Ni3Se2 nanosheets also have good dispersion on rGO.NiSe-Ni3Se2 nanosheets are with the hollow hexagonal nanosheets,the small hollow structure can increase more active sites and promote better HER activity.In the alkaline,neutral and acidic electrolytes,NiSe-Ni3Se2/rGO also has a smaller overpotential at the current density of 10 mA·cm-2 and a smaller Tafel slope,meaning good HER performance.Heterostructure can promote electron transfer by modifying the electronic structure to get high conductivity and mass transfer efficiency.MoS2 is a widely studied material,MoSe2 and MoS2 have the similar structure,MoS2 has higher intrinsic conductivity and lower ΔGH*than that of MoSe2.So MoSe2 was as research foundation,combining the low cost of transition metal cobalt,CoSe2-MoSe2 heterojunction electrodes were prepared with different proportion of Co/Mo.The best Co/Mo proportion of 1:1 was determined by the performance analysis in acidic and alkaline electrolytes.The bimetallic CoSe2-MoS2(1-1)/rGO heterojunction electrode was prepared by further compositing rGO.In alkaline and acidic electrolytes,the overpotential(at 10 mA·cm-2)and Tafel slope of CoSe2-MoSe2(1-1)/rGO are significantly lower than those of other comparative materials.The interfacial electronic properties of CoSe2-MoSe2 heterojunction and its ΔGH*were investigated in detail by density functional theory(DFT)calculation.The result proves that,compared with CoSe2 and MoSe2,CoSe2-MoSe2 heterojunction has the narrower band gap and ΔGH*,which can accelerate the reaction kinetics and improve the HER activity by promoting faster electronic conductivity.Transition metal Fe element in the earth’s crust has the advantages with the high storage(5%)capacity and low cost.The price of iron is almost two orders of magnitude lower than that of metal Ni and metal Co,which can significantly reduce the cost of synthesis technology and accelerate its commercial rationalization.Therefore,the combination of FeSe and MoSe is considered.FeSe2-MoSe2 heterojunction hydrogen electrodes were prepared with different proportion of Fe/Mo using one-step hydrothermal method.Through the analysis of HER performance tests in acidic and alkaline electrolytes,the best Fe/Mo proportion of 1:1 was determined.The bimetallic FeSe2-MoSe2(1-1)/rGO heterojunction electrode was prepared by rGO recombination.At 10 mA·cm-2,the overpotential and Tafel slope of FeSe2-MoSe2(11)/rGO in alkaline electrolyte are smaller than those of other comparative materials.In acid electrolyte,the overpotential(10 mA·cm-2)and the Tafel slope of FeSe2-MoSe2(1-1/rGO are also smaller than those of other materials.DFT shows that compared with MoS2,FeSe2-MoS2(1-1)/rGO has smaller density of states(DOS)of Se-H and Mo-H bonds.And it has a lower work function,suggesting that it needs a small additional voltage input to drive the HER process,which is conducive to better HER activity.In order to further improve the HER activity,the use of impurity atoms doped heterojunction to regulate electronic structure and optimize the intrinsic activity of the catalyst.In addition,the carbon cloth as a matrix,composite materials to make self-supporting electrode can avoid the use of the binder.In addition,considering Ni-Mo has the better HER properties than Fe-Mo,and NiSe2 is a material with a low resistivity.So NiSe2-MOSe2 heterojunction electrode was prepared with different proportion of Ni/Mo by one-step hydrothermal method.The best Ni/Mo proportion of 1:1 was determined by the analysis of performance tests in acidic and alkaline electrolytes.The P-NiSe2/MoSe2(1-1)@CC heterojunction electrode was obtained by P-doped.In alkaline or acidic electrolytes,compared with other comparative materials,PNiSe2/MoSe2(1-1)@CC has the smallest overpotential(at 10 mA·cm-2)and Tafel slope.The effect of P doping on hydrogen evolution was investigated by DFT calculation.The calculation results shows that the density of electronic states near Fermi level of P-NiSe2/MoSe2(1-1)is significantly enhanced,which proves that it has better electron transport capacity and promotes the faster HER reaction.