Electrodeposition Of Nickel-based Alloys From Deep Eutectic System And Their Electrocatalytic Properties

With the rapid economic growth,the energy crisis and environmental pressure need to be solved.Hydrogen energy is favored because of its high calorific value,renewable and pollution-free advantages.Hydrogen production from water decomposition is preferred to obtain hydrogen because of its wide range of raw materials and no pollution.However,the cost of hydrogen production from the decomposition of water is too high to meet the wide application in the market due to the low transformation effenciency.Hydrogen evolution catalyst can effectively reduce the interface resistance of hydrogen electrode,decrease the cell voltage and accelerate the reaction speed,which is expected to fundamentally solve the problems existing in the current hydrogen production industry.Pt and its alloys can be served as the best catalysts for improving the hydrogen evolution reaction efficiency.However,because of its high cost and limited reserves,it cannot meet the application requirements.Therefore,a low-cost hydrogen evolution catalyst with less Pt or Pt-free attracts an increasing attention.Nickel and its alloys can freely gain and lose electrons to form electron pairs or complexes due to the unfilled state of d electron orbital.The ligand and receptor coordination will form active sites,resulting in a catalytic effect.Therefore,nickel and its alloys have broad application prospects as low-cost and efficient catalytic materials.Due to the particular structure of ionic liquids,the alloy composition and internal structure can be controlled.Therefore,the electrodeposition of nickel-based alloys in the deep eutectic solvent is expected to obtain high-performance hydrogen evolution catalysts.In this study,Ni-P,Ni-Mo and Ni-Mo-P alloys were electrodeposited in a choline chloride-ethylene glycol deep eutectic solvent(CE).The catalytic activity of hydrogen evolution was valued to optimize the synthesis conditions of nickel-based alloys.The main conclusions are listed as following:(1)Ni-P alloy in CE mainly relies on instantaneous nucleation and formed under diffusion control.The existence of P changes the charge center of Ni-P alloy,and also promotes the formation of nanocrystalline in the alloy.The 0.3Ni-0.05P alloy electrodeposited at 70℃and 7 mA·cm-2 has the smallest grain size with a best hydrogen evolution catalytic activity(η100=170 mV,b=50.8 mV·dec-1)and good catalytic stability(△η100=7.4 mV/1000 cycles);(2)Ni-Mo alloy is formed by multi-step reduction of Ni(II)and MoO2Ni4 intermediate.With the increasing Mo content in the alloy,the grain size increases gradually,and shows an amorphous transformation.The intrinsic activity of Ni-Mo alloy also increases with the increasing Mo content.The 0.6Ni-0.21Mo alloy electrodeposited at 70℃ and 30 mA·cm-2 has not only high Mo-content but also large surface roughness,leading to a best hydrogen evolution activity(η100=150 mV,b=48.7 mV·dec-1),but the stability is low;(3)Current density influences the grain size,alloy content and phase composition of Ni-Mo-P ternary alloy.With the increase of current density,the grain size of the alloy gradually decreases,the Mo content increases,but the P-content decreases,and the alloy gradually transits from Ni(Mo,P)to the mixture of Ni4Mo and Ni(P).The charge transfer among Ni,Mo and P elements in the alloy promotes more active sites.The 0.6Ni0.21 Mo-0.066P alloy prepared at 30 mA·cm-2 and 70℃ has the optimal hydrogen evolution catalytic activity(η100=146 mV,b=43.6 mV·dec-1)and excellent catalytic stability(△η100=9.3 mV/1000cycles).