| As the most mature technology to produce Hydrogen,alkaline water splitting possesses simple structure,normal temperature and can be combined with renewable energy to make large-scale Hydrogen storage,which exhibits wide prospect in energy storage.While,its operating current density is relatively low.And due to the employment of highly corrosive electrolyte,metal parts are easily corroded and thus causes a decrease of electrolysis efficiency.Noble metals,such as Pt,Ir,exhibit excellent catalytic performance.However,due to the extremely high cost,noble catalysts are unable to be deployed in large-scale applications.As an alternative to noble metal catalysts,transition metal Ni presents excellent alkaline corrosion resistance ability and lower catalytic ability compared to noble metals.Moreover,its low cost and high abundance make it the most widely used electrode material.It has been proved that a larger active surface area can provide more active sites for the electrolysis reaction,effectively improving the performance of water splitting.Therefore,Ni-based porous catalyst is prepared by surface modification technology to improve electrode catalytic performance which has become the important research direction in the field of Hydrogen produced by water splitting.High-pressure cold spray is a novel surface modification technique.In a cold spray process,metal particles are accelerated to a higher speed by a high-pressure and high-speed gas,then impact substrate surface and experience plastic deformation to form a coating.The process is suitable for large-scale preparation of catalyst coatings to water splitting due to its high efficiency.And metal particles don't be melted and oxidized in the whole cold spray process,thus the preparation of metallurgical binding coatings can be achieved.This subject intended to use Ni/Al mixed powder as feedstock,and catalytic coatings with different porous structures were obtained by adjusting the Al volume fraction.The coatings with gradient structures were obtained by controlling the deposition sequence of the coating with different pore former content.And to further increase the binding strength between coatings,post annealing was adopted to eliminate the residual stress in the coating.SEM,EDS,XPS,XRD and industrial CT were implemented to check the micromorphology and structure of coatings.Electrochemical tests such as LSV,CV,OCV,Tafel slope and Cdl were used to characterize electrochemical properties of coatings.The effects of the porous structures of catalytic coating on electrode properties and mass transfer during electrolysis were studied.In addition,the impact mechanism of the coating structure of Ni electrode on its catalytic performance was discussed,to clarify the mechanical relationship between high-performance electrode coating structure and performance.The results show that the increase of Al addition brings the larger porosity of coating.When the Al content is 20%,the coating porosity can reach 38.5%,which greatly increases the surface area of the electrode and thus the electrode performance is significantly improved.A suitable post annealing temperature can cause interdiffusion of Ni and Al in the coating to form alloy phases of Ni Al and Ni3Al,which effectively enhances the binding strength of the coating,and ensures the porous structure of coatings to bring electrodes excellent electrolysis performance.To achieve a current density of 10m A.cm-2,the HER overpotential of electrode only needs 30 m V.The mass transfer capability inside pores is effectively improved due to the introduction of the gradient porous structure,further improves the catalytic activity of the electrode.When the current density is 60 m A.cm-2,the HER overpotential only consumes 480 m V,and the OER current density can reach 80 m A.cm-2 at the potential of 1.6 V.It indicates that the catalytic performance is improved approximately 60%compared to sample N30A.Meanwhile,the sample exhibits an excellent durability,and thus is suitable as the electrode of water splitting. |
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