Electrocatalytic Water Splitting In Alkaline On Nickel-based And Carbon-based Catalysts With Heteroatomic Doping

Hydrogen is considered as an ideal candidate to alleviate the dependence on fossil fuels by virtue of its high mass energy density,renewability.And it appears to be a promising energy carrier for the future.Water electrolysis represents one of the most promising and appealing approaches for large-scale,ecofriendly,and sustainable hydrogen production.However,the high cost and low efficiency of water electrolysis seriously hider its large-scale application.Exploring inexpensive,efficient,and stable catalysts to reduce the cost and improve the efficiency of water electrolysis is of great significance to realize the large-scale water electrolysis.Based on this,this thesis aims at achieving efficient,cheap and stable electrocatalyst for water splitting,clarifying the reaction mechanism,and constructing a large-scale electrolytic water system.We try to study the relationship between the structure and activity in three aspects:material design,reaction mechanism and operating condition.This thesis provides scientific basis and theoretical guidance for design and development of practical water electrolyzer catalysts.The main results are as follows:(1)Water splitting of Ni Co bifunctional catalyst in alkaline.Ni Co catalyst was used as the research object to explores the design and development of practical Ni Co electrolytic water catalyst.A plasma thermal spraying assisted method which is simple and easy to be amplified was used to prepare the Co doped Ni catalyst(Ni Co_0.08).Thanks to the special structure produced by the plasma thermal spraying assisted method and the addition of Co,the Ni Co_0.08catalyst has excellent OER activity(?_{10 m A cm-2}=210 m V and?_{100 m A cm-2}=266 m V)and good HER activity(?_{10 m A cm-2}=106 m V and?_{100 m A cm-2}=194 m V),demonstrates its efficient bifunctional performances of water splitting.The overpotential reached 500 m A cm^-2 of the system used Ni Co_0.08 catalysts are 140 m V and 160 m V lower than that of Ni catalysts and commercial Raney-Ni catalysts under the condition of industrial water electrolysis(30 wt.%KOH,80 ^oC),respectively.Furthermore,the activity is without any deviation after 280 hours of continuous operation.The result in industrial electrolytic water plant shows that the cell voltage of Ni Co_0.08 catalysts is about 100 m V lower than that of commercial electrolytic water catalysts under the same conditions,and the activity shows almost no change after continuous operation for 172 hours.Those results indicate that Ni Co_0.08 catalyst has great potential for practical application.(2)The alkaline HER performance and mechanism of Ni Mo electrocatalyst.The effect of Mo on the surface of Ni for HER was studied by using a Ni Mo catalyst with Mo atomic dispersion.It was found that the incorporation of atomically dispersed Mo could greatly improve the HER activity.The overpotential of Ni Mo catalyst at 10 m A cm^-2 in 30 wt.%KOH is 21 m V and the Tafel slope is 49 m V dec^-1.The TOF normalized with the surface Mo content reaches 246.67 H₂ s^-1at?=100 m V.The overpotential reached 400 m A cm^-2 of the system used Ni Mo catalyst as the cathode and Ni catalyst as the anode is 133 m V and 140 m V lower than that of Ni catalyst and commercial Raney-Ni catalyst under the condition of industrial water electrolysis(30 wt.%KOH,80 ^oC),respectively.And the activity after 3000 hours of continuous operation is a little better than the beginning.Those results indicate that Ni Mo catalyst has great potential for practical application.DFT calculation results show that Mo in Ni Mo is the adsorption active site of H₂O and Ni nearby Mo in Ni Mo is the adsorption active site of H.The incorporation of Mo can not only adjust the local electronic structure of Ni,but also promote the adsorption and dissociation of H₂O in the HER process.(3)The HER active sites and mechanism of nitrogen-doped carbon catalysts.The effect of nitrogen in nitrogen-doped carbon on HER was investigated by using ordered mesoporous carbon as a model catalyst.The interface structure and electrochemical evolution of nitrogen-doped carbon electrocatalysts at different p H values were studied by using proton reduction as the probe reaction.It is found that the doped nitrogen atoms on the surface of nitrogen-doped carbon catalysts are the active sites of H in HER process,and the HER activity of nitrogen-doped carbon catalyst can effectively improve by increasing the surface nitrogen content.In acidic media,the HER process of nitrogen-doped carbon catalysts follows the Volmer-Heyrovsky mechanism,the protonation of surface-active nitrogen atoms promotes the Volmer step,and the rate-determining step is Heyrovsky step.In alkaline media,the HER process of nitrogen-doped carbon catalysts also follows the Volmer-Heyrovsky mechanism as the Tafel slope is 70-90 m V dec^-1.