Study On Photocatalytic/Electrocatalytic Hydrogen Evolution By Transition Metal Compounds (Co_0.85Se,Cu₃P)

In recent years,it has been found that transition metal compounds(Co_0.85Se,Cu₃P)have excellent electrocatalytic properties.The transition metal electrocatalyst was used as a cocatalyst supported on the surface of the photocatalyst to form an excellent visible photocatalytic heterojunction materials for hydrogen production.Secondly,the transition metal compounds supported on highly conductive carbon materials are beneficial to enhance the conductivity and accelerate the electron transfer rate to realize the efficient performance of electrocatalytic hydrogen production.The specific research contents are as follows:（1）Co_0.85Se,as an excellent electrocatalytic activity,was used as a cocatalyst to modify Cd_0.5Zn_0.5S nano-photocatalyst.The Co_0.85Se（1.5 wt%）/Cd_0.5Zn_0.5S Schottky junction shows the greatest activity for H₂generation(759.3μmol h^-1),which is 2.1 times that of bare Cd_0.5Zn_0.5S(350.6μmol h^-1).It is noted that exfoliated metallic Co_0.85Se nanosheets show a little better hydrogen evolution reaction property and a smaller charge-transfer resistance than those of Co_0.85Se nanoplates,implying that exfoliated Co_0.85Se nanosheets have more active sites and higher electrical conductivity.The distinct properties of exfoliated metallic Co_0.85Se nanosheets enhance the efficient spatial separation of photoinduced charged particle carriers and result in an excellent enhancement in the photoelectric current and photocatalytic hydrogen evolution performance of Cd_0.5Zn_0.5S.（2）Co_0.85Se magnetic nanoparticles supported on carbon nanotubes were prepared by one-step hydrothermal method.Moreover,MWCNTs as an carbon materials with electrical conductivity is relatively high could enhance mass transport during electrocatalytic reactions.What is more,in acid solution,30 wt%MWCNTs/Co_0.85Se composites catalyst provided a current density of 10 m A cm^-2at a small overpotential of266 m V vs.RHE and a small Tafel slope of 60.5 m V dec^-1.These results demonstrates that MWCNTs/Co_0.85Se exhibit excellent hydrogen evolution reaction performance and a better long-term stability for HER.（3）In the absence of organic solvent solution,Cu₃P nanowires were synthesized by one-step hydrothermal method by copper chloride and red phosphorus,Cu₃P/Ti O₂heterojunction achieve efficient photocatalytic hydrogen production efficiency.The surface valence distribution and the energy band structure of Cu₃P and Ti O₂were analyzed by XPS spectrum and UV-vis spectrum.Moreover,PL spectrum,photocurrent test and electrochemical impedance spectra were used to clearly analyze the hydrogen production mechanism of Cu₃P and Cu₃P/Ti O₂.These results displayed that the 10 wt% Cu₃P/Ti O₂possess higher hydrogen evolution(2429.8μmol g^-1h^-1),which prove Cu₃P as cocatalyst can effectively restrain photoinduced e^-/h⁺recombination and increase the activity surface area of Ti O₂,so as to enhance the photocatalytic activity of Ti O₂.（4）Cu₃P and rGO/Cu₃P electrocatalysts were prepared by one-step hydrothermal method,X-ray powder diffraction（XRD）and scanning electron microscopy（SEM）were used to analyse their crystal structure and microstructure.In acidic solution,40 wt%rGO/Cu₃P shows lower initial potential（106 m V vs.RHE）and a small Tafel slope(93.7m V dec^-1).Stability test was performed by 1000 cycles LSV polarization curve at a scan rate of 5 m V s^-1,the results showed that rGO/Cu₃P had excellent long-term stability in acidic solution.