Transition-metal Phosphide-based Electrocatalysts: Preparation And Property For Hydrogen Evolution

Hydrogen?H₂?,with the highest gravimetric energy density among all chemical fuels,is considered as the best carrier to replace fossil fuels as a new clean energy source.Hydrogen evolution reaction?HER?from electrolytic water is an important way to produce hydrogen.To reduce energy consumption,the efficient electrocatalysts for HER are indeed required to provide high current density at low potential.Among various HER catalysts,transition metal phosphides?TMPs?are widely used as HER catalysts due to their abundant content,low cost and high catalytic activity.In this paper,the catalysts of NiP₂-Ni₅P₄/CFP,FeP@PC and Cu₃P/CuCl@PANI were synthesized by simple methods.The effects of carbon support on the catalytic properties of TMPs were studied.The main research conclusions were as follows:?1?NiP₂-Ni₅P₄/CFP composite catalysts were prepared on carbon fiber paper?CFP?by simple hydrothermal method and chemical vapor deposition?CVD?phosphating.The results of electrochemical performance test showed that the NiP₂-Ni₅P₄/CFP catalyst showed excellent performance with a low onset overpotential 29.6 mV,a low overpotential?122 mV?at 10 mA cm^-22 and a small Tafel slope of 87 mV dec^-1 in acid electrolytes.In 1 mol/L KOH,the onset overpotential was 33 mV,the required overpotential at 10 mA cm^-2 was 177 mV and the Tafel slope was 98 mV dec^-1.Therefore,the NiP₂-Ni₅P₄/CFP catalyst remained to be efficient catalyst both in acid and alkaline media.By cyclic sweep voltammetry and chronoamperometry,the NiP₂-Ni₅P₄/CFP catalyst exihibited superior stability in acidic and alkaline media.?2?Using the mental organic framework?MOF?UIO-66 as the substrate,the FeP@PC electrocatalyst was prepared by carbonization,chemical vapor deposition?CVD?and in-situ phosphating by NaH₂PO₂ and etching by hydrofluoric acid.The effects of Fe content on the morphology and properties of the FeP@PC catalyst were also studied.Results showed that with the increase of Fe content,the catalytic performance of the final product FeP@PC is gradually improved.When the molar ratio of Fe to ZrCl₄ increased to 5:1,the final product FeP@PC?5:1?showed excellent HER catalytic performance and stability.The onset overpotential of FeP@PC?5:1?was 67mV,and the overpotential required for 10 mA cm^-2 was 145 mV.After cyclic sweep voltammetry and working for 8 h at 145 mV by chronoamperometry,the current density did not decrease significantly,manifesting that the FeP@PC?5:1?had superior stability.?3?The Cu₃P/CuCl hybrid nanorods were synthesized by simple hydrothermal method in one step.The effect of the molar ratio of CuCl to P and the reaction temperature on Cu₃P/CuCl hybrid nanorods was studied.In addition,the dispersion and electrochemical properties of Cu₃P/CuCl hybrid nanorods were improved by the encapsulation of PANI.Results showed that the optimum conditions for the preparation of Cu₃P/CuCl hybrid nanorods were the feed ratio of 1:1 and the reaction temperature of200?.The dispersion,electrochemical properties and electrochemical stability of Cu₃P/CuCl@PANI were better than that of Cu₃P/CuCl nanorods.When the electrochemical performance was tested in 0.5 mol/L H₂SO₄,The onset overpotential of Cu₃P/CuCl and Cu₃P/CuCl@PANI were 165 and 140 mV and the Rct were 583 and 136?,respectively.After 1000 cycles,the overpotential of Cu₃P/CuCl@PANI at current density 4 mA cm^-2 increased by only 21 mV.