| In order to promote the large-scale industrial application of water electrolysis to product hydrogen,iron metal porous films were electrodeposited on Gas-Liquid-Solide(GLS)interface.However,for iron metal,it is easy to form single-scale micron-sized particles and pores by using electrodeposition,and the micro-structure is difficult to control.So,the catalytic activity is low.In addition,the understanding of the intermediate process of film morphology evolution is lack,and there is no common formation model of porous film,and the pore structure evolution mechanism is unclear.In order to solve the above bottleneck problem,taking nickel for an example,the rules and mechanisms of pore formation and pore structure evolution were investigated.A porous structure formation model based on the growth of the protuberance was established,and a method of film morphology control based on the wettability was proposed.Then,self-supporting NiAg and CoP-based films with with micro/nano porous structure were prepared to provide technical and theoretical support for the large-scale industrial application of water electrolysis to product hydrogen.The effect of electrodeposition kinetics on the formation of porous Ni films was investigated,and the key factors for the determination of porous nickel films electrodeposited on gas-liquid-solid interface were determined.The results show that NH4+ can make nickel electrodeposition continuously proceeds,which is the necessary condition for the porous structure formation.The chemical structure of discharge ion has a great influence on the morphology of nickel film.The stronger the chemical structure of nickel discharge ion is,the more inhibited the nucleation of nickel crystal.As a result,the grain size of nickel is larger,and the isotropic growth ability of the film is stronger.So,it is not conducive to form porous structure.By comparing the differences between the iron metals and non-iron metals,it is found that the non-iron metals with high exchange current density and low melting point are easy to form dendrites which develop to porous structure.While,for the iron metals with small exchange current density and high melting point porous structure is difficult to form.Sodium lauryl sulfate can reduce the pore size and pore wall thickness,increase pore density and make the porous structure more uniform.The effects of NH4Cl on the formation and evolution of porous nickel sturcture were investigated.It was found that when the concentration of NH4Cl is low(0.2 M-0.35 M),the mass amount of electrodeposited Ni is less than the critical deposition of porous formation,so,a compact film was formed.When NH4Cl concentration is higher than 0.4 M,Ni electrodeposition process continued,resulting in the formation of protrusions,and the protrusions rapidly grow to form porous structure.Protrusion formation and critical nickel deposition are necessary for porous formation.On the basis of this,a model of porous structure formation based on the growth of the protrusion was established.In the early stage of metal electrodeposition,it was controlled by complete linear diffusion to produce a dense and flat nickel film.With the increase of the nickel ion concentration gradient,hydrogen evolution reaction is aggravated.A large number of insulating hydrogen bubbles change the electric field lines and ion concentration distribution on the surface of the electrode,and the protrusions are formed.When the protrusions reach the height of the critical protrusions,the tip changes from linear diffusion to spherical diffusion control,and the protrusions grow rapidly around the bubbles to form porous structure.At the same time,it was found that when the concentration of NH4Cl(greater than 0.75 M),the species of nickel ions changed,resulting in the increase of pore density and the decrease of the pore size.In order to investigate the effect of wettability on the bubble properties and the morphology of the film,the wettability of GLS interface was adjusted by liquid and solid phases.A method to control film morphology was proposed based on the wettability.It was found that C12H25SO4Na can reduce hydrogen bubble diameter,and decrease bubble residence time,and increase bubble nucleation density by making the surface tension and contact angle lower,which makes the bubble nucleation more uniform on the electrode plate.Therefore,the pore size of the nickel film is reduced,and the pore density is increased,and the pore structure is more uniform.On ultra-hydrophilic surface,radius of the bubbles were small,and it’s residence time was short.As a result,a compact and flat film was obtained because the protrusions did not reach the critical growth height.On compact copper film surface,as bubble residence time was moderate and bubble nucleation was uniform,the protrusion reaches the critical height of growth.The top of the protrusion changed from linear diffusion to spherical diffusion,and it grow rapidly to form porous structure.On superhydrophobic surface,the surface of the films was covered by a layer of bubbles,and Ni was electrodeposited on the bubbles,which result in the films structure was irregular,and has a poor bonding with the substrate.In the process of Ni electrodeposition on the GLS interface,Ag,which possess high exchange current density and low melting point,was introduced to obtain a NiAg film with micro/nano porous structure.The thickness of NiAg film was increased from 7 μm to more than 20 μm,and the roughness of NiAg film was increased(4352).As a result,the hydrogen evolution activity was enhanced due to the increase of the effective activity area.The water electrolysis stability of NiAg film was well and the voltage was low.The surface wettability of NiAg film was well,and the contact angle was only 19 °,which was conducive to the rapid separation of bubbles and reduce the ohmic voltage drop.Therefore,the low hydrogen evolution overpotential and good wettability of NiAg film greatly reduce the cell voltage.CoP porous films electrodeposited on GLS interface were treated by phase separation,thermal oxidation and selective etching to control the morphology and the phase distribution.Dual-phase Co2P-Co3O4 porous catalysts for OER and the outer layer rich C02P phase hierarchically porous films for HER were obtained.The catalytic activity of CoP-based thin films and the stability of water electrolysis at high current density were systematically investigated.The results show that the presence of Co2P phase can improve the conductivity of Co3O4 to enhance the catalytic activity.After etching,the active area of CoP-base films increased,and more highly active Co2P phase was exposed on the surface,as a result,the hydrogen evolution activity was enhanced.The stability was improved because the inner Co phase transition layer in the CoP-base film enhanced the binding force between the film and the substrate.Assembled CoP-400-IO||CoP-400-E15 Electrolytic Water Cell was stable at high current density(500 mA cm-2)with low cell voltage. |
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