Study Of Ni-S Alloy Cathodes And Mechanism Of Hydrogen Evolution Prepared By Electro-deposition

In all the mature hydrogen production techniques the water electrolytic production of the hydrogen energy is the most applicable technique.However,the iron and Raney-nickel electrode of the electrolytic technique used nowadays result in high energy consumption due to the high hydrogen evolution reaction(HER) potential.Thus,to develop and use the hydrogen energy in large scale,the HER potential must be decreased.Recently,Ni-S and Ni-S-based alloys have gain important considerations in hydrogen production field due to the low HER potential.In this paper,the amorphous Ni-S and Ni-S-based tertiary alloy electrode have been produced on different nickel substrates,and the crystal structures and the hydrogen evolution activity have been studied. Based on the investigations,the following conclusions are drawn:1.Ni-S alloy electrode on nickel net substrate has been produced. The best electrodepositing conditions have been experimentally determined.The results of the hydrogen evolution properties indicated that the content of S in the coating has large effect on the hydrogen evolution properties of the electrode.The Ni-S alloy electrode has very low HER potential when the content of S is between 15～19%.2.The amorphous Ni-S alloy electrode has been produced on nickel foam substrate.Compared to nickel net substrate,the hydrogen evolution properties of nickel foam substrate have obviously been improved since the nickel foam substrate has special pore structures and large true surface area.In modeling the industrial electrolysis conditions for 24 hours,the cell volt of the nickel foam substrate was decreased by 0.17 V and 0.26 V at current densities of 200 mA·cm^-2 and 400 mA·cm^-2,respectively,which substantially decreases the energy consumption in electrolytic production of hydrogen.3.Ni-S-based tertiary alloy electrodes have been produced by adding Co,La and Mo ions.The experimental results indicated that all the above mentioned metal ions can improve the hydrogen evolution activity of nickel foam substrate based amorphous Ni-S alloy electrode.However, only Ni-S-Co and Ni-S-La alloy electrodes have both excellent hydrogen evolution properties and electro-chemical stability,and have high real application merit for hydrogen electrolytic production industry.4.On the first time,the Ni-S electrode with gradient distribution of S and the Ni-S-Co electrode with gradient distributions of S and Co in the coating have been produced using gradient electrolytic process.This gradient distribution can help decrease the coating internal stress and increase the coherence between the coating and the substrate,and improve the electro-chemical stability and lifetime.Thus,they are good hydrogen evolution cathode materials for future applications.5.The rare earth element oxides Er₂O₃ and Pr₂O₃ have been added to the electroplating solution.The experimental results indicated that the grain size of the coating decreases and surface area increases as the concentration of the additives increase,which is probably due to the inhibition of the grain growth by Er₂O₃ and Pr₂O₃ particles on the coating surface.However,the addition of the Er₂O₃ or Pr₂O₃ can help improve the hydrogen evolution activity.6.The heat treatment program after electrodeposition has been studied.It has been shown that Ni-S alloy coating can change from amorphous state to crystalline state after heat treatment under argon atmosphere,thus increase the HER potential,while the HER potential during water electro-deposition can be decreased a lot after heat treatment under alkali solution.7.The calculated activation energies are 49.5,40.3 and 38.6 kJ mol^-1 for nickel foam electrode,nickel foam substrate based Ni-S alloy electrode and Ni-S-Co alloy electrode according to Tafel curves, respectively,which gives explanation about the difference in hydrogen evolution activity from energy angle.The results indicated that the high hydrogen evolution activity of Ni-S alloy electrode is due to the large absorption of the hydrogen atoms during hydrogen evolution process.The catalysis principle is electro-chemical desorption principle.