Preparation Of Ni Co-based Composites And Their Applications In Hydrogen Evolution Reaction

With the development of nanotechnology,functional nanomaterials are gradually becoming research hotpots.The properties of materials are related to their surface morphology and chemical components.NiCo-based composites are widely applied in the fields of lithium batteries,super capacitors and water splitting.Different synthesis conditions and chemical components of NiCo-based composites may greatly influence the size,structure and morphology of materials,thus change the catalytic activity.In this work,with the method of morphology design,heteromorphic NiCo₂S₄/Ni₃S₂/NF composites,NiCo₂S₄/NF nanowire arrays and NiCoP/NiP₂/NF composites were prepared via different methods and we further investigated the influence of morphology to the electrocatalytic activity of bimental composites.The structures of as-made samples were characterized by X-ray diffractometer,field emission scanning electron microscopy,transmission electron microscopy and so on.The performances of obtained composites as free-standing electrodes for hydrogen evolution reaction were investigated.The main contents and results are as following.1.NiCo₂S₄/Ni₃S₂/NF was prepared from nickel nitrate hexahydrate,Cobalt nitrate hexahydrate,nickel foam and sulfur powder.NiCo₂S₄ and Ni₃S₂ were in-situ grown on the nickel foam in the shape of nanoflakes and nanospheres,respectively.The co-synergistic effect and the uniqie heteromorphic facilitated the mass transfer of electrolyte and accelerated the electron transfer effectively,thus enhanced the HER performance.When sulfurized with 1g sulfur powder for 1 h,the NiCo₂S₄/Ni₃S₂/NF-1 sample exhibits best electrocatalytic activity.In alkaline solutions,the resultant Ni₃S₂/NiCo₂S₄/NF-1 exhibits extremely low onset overpotential（15 mV）,a relatively small tafel slope(105 mV·dec^-1),small EIS（2Ω）and high cycling stability.2.NiCo₂S₄/NF nanowire arrays were fabricated through a facile hydrothermal and sulfurization method.It is found that the surface roughness of NiCo₂S₄/NF was very high,which promoted the escape of H₂.But over sulfurization would destroy the uniform structure,which was negative for HER performance.The three-dimensional conductive NiCo₂S₄/NF possesses good elelctrocatalytic activity.The sample sulfurized with 400 mg TAA for 6 h exhibits an overpotential of 196 mV at a current density of 10 mA·cm^-2 and still keeps a current density of 340 mA·cm^-2 under-0.5 V.3.NiCoP/NiP₂/NF were prepared from NiCo/NF via phosphatizing.The great HER activity of resultant NiCoP/NiP₂/NF can be ascribed to the bi-synergistic system formed through morphology designing and defect construction.The NiCoP/NiP₂/NF sample shows an overpotential of 59 mV at a current density of 10 mA·cm^-2 and a low EIS of 1.3Ω.After cycling for over 24 h,the structure of NiCoP/NiP₂/NF rentained and there was no obvious decay of current density.The NiP₂ nanoparticles were uniformly grown on the NiCoP nanowires and there were two synergistic effect in the system,furthermore,the introduction of P atoms expedited the desorption of absorbed hydrogen and enhanced the bubbling effect,therefore,NiCoP/NiP₂/NF possessed the best electrocatalytic activity among these three composites.