Synthesis And Characterion Of Nickel Carbide(Phosphide)/Carbon Composites And Their Electrochemical Hydrogen Evolution Properties

Non-noble metal nickel?Ni?containing unsaturated d shell orbit,the special structure is beneficial for the adsorption of hydrogen ions?H+?.In addition,nickel combinated with other compounds to form be alloy,and it has the advantages of corrosion resistance and deposit easily.So nickel is one of the major components of hydrogen electrode materials.Carbon materials with excellent electric conductivity,which accelerate the rate of electron transfer and reduce the hydrogen evolution overpotential???during the electrochemical reaction.Comprehensive the above reasons,we synthesized Ni@Ni₃C/SWCNTs,Ni-C@Ni2P-400 and Ni2P/C composites,respectively in this paper.Different kinds of electrodes were constructed which modified with the three catalysts on the surfaces of glassy carbon electrode?GCE?,and used for the study of electrochemical hydrogen evolution performance.The main works are as follows:?1?In this work,the Ni@Ni₃C/SWCNTs was synthesized by a facile one-step hydrothermal method which choose nickel chloride hexahydrate?NiCl2·6H2O?and2-methyl imidazole with single-walled carbon nanotubes as raw material.The morphology and structure of the materials were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscopy?TEM?etc.The results showed that the SWCNTs induce Ni@Ni₃C with a typical one-dimensional chain structure into disorder particles.In the meanwhile,SWCNTs as one dimensional conductive material intertwine between the Ni@Ni₃C particles.Electrochemical testing results displayed that the Ni@Ni₃C/SWCNTs has the better catalytic performance compared with the Ni@Ni₃C and SWCNTs due to the synergistic effect of Ni@Ni₃C and SWCNTs.The Ni@Ni₃C/SWCNTs composite with a low onset overpotential of-52 mV and a Tafel slope of 46.8 mV·dec-1,acquired an exchange current density of 35.5×10-3mA·cm-2.Using cyclic voltammetry?CV?and the time-current method?I-T?for further study,the results indicated that Ni@Ni₃C/SWCNTs modified electrodes can maintain its catalytic activity for over 24 hours in 0.5 M H2SO4 solutions,and the cathode current without no obvious change.All of the above result stated that material has outstanding catalytic stability in hydrogen evolution.?2?In this work,we prepared ZIF-67?Ni?in room temperature using NiCl2·6H2O and 2-methylimidazole as raw material.Then,Choose the Metal Organic Framework?MOF?materials as precursor,phosphorization in a porcelain boat with NaH2PO2 under 400 °C in the flow of N2 gas,and maintained at this temperature for 2h.The morphology and structure of the materials were characterized by SEM,X-ray spectra?EDX?,XRD,X-ray photoelectron spectroscopy?XPS?and Raman spectroscopy?Raman?.Results show that the block carbon-nickel surface grow many orderliness Ni2 P nanorods during the phosphating process,the average size of particle is about 0.30 0.45 microns.The electrochemical testing results displayed that the Ni-C@Ni2P-400 composite electrode with a low onset overpotential of-85 mV and a Tafel slope of 92.1 mV·dec-1 in 0.5 M H2SO4 solution,and acquires an exchange current density of 14.2×10-3 mA cm-2.Using CV and I-T methods to further study its stable performance,the results indicated that the cathode current maintain within a certain range in the 24 hours,it is means that the material has good activity for hydrogen evolution.?3?In this work,The hexagon rod Ni-MOF-74 were synthesized by microwave method which use nickel nitrate hexahydrate?Ni?NO3?2·6H2O?as transition metal source and 2,5-dihydroxy terephthalic acid?H4dhtp?as bridging ligands.Then,the Ni-MOF-74 precursor phosphorization in the tube furnace under the protection of N2 gas,which choose NaH2PO2 as the phosphorous source.Finally,the black powders Ni2P/C were achieved after the sample was naturally cooled to room temperature.The morphology and structure of the materials were characterized by SEM,XRD,EDX,TEM and XPS.Test results indicate that the smooth surface of hexagon rod Ni-MOF-74 into a porous structure after the phosphating reaction.The performance test results displayed that the Ni2P/C composite electrode with a onset overpotential of-94 m V and a Tafel slope of 118.9 mV·dec-1in 0.5 M H2SO4 solution.Furthermore,the obtained modified electrode can maintain its catalytic activity in a period of time.