Fabrication of Gradient Porous Ni Electrodes by Selective Laser Melting and Their Performance in Water Electrolysis for Hydrogen Production
Nickel stands out as a widely utilized material in alkaline water electrolysis for hydrogen evolution electrodes.It has been proved that the efficiency and energy consumption for H2 production can be effectively optimized by increasing the porosity of Ni electrodes.However,the systematic exploration of the effect of pore size and gradient remains lacking.To address this gap,this work was initiated.Four sets of porous electrodes with controlled pore size and gradient were designed.Laser selective melting was then applied to fabricate the designed electrodes with high precision.The hydrogen evolution characteristics and performance of the resulting samples were comprehensively investigated through the analysis of surficial morphology,sectional microstructure,electrochemical performance,stability,and kinetics evaluation.The results showed that all the prepared samples exhibited a rough surface with numerous adhered particles,providing abundant active sites for hydrogen reactions.The high energy density of the laser led to the melting and coagulation of metallic particles,forming a porous structure in all samples.Consequently,all samples exhibited excellent electrolysis stability,showing no visible performance degradation after stability testing.Nyquist plots and the Bode plots reveled that samples without gradient exhibited a thin and dense bubble layer during electrolysis,leading to higher capacitive resistance and a lower frequency of the maximum phase angle.In contrast,the gradient samples displayed larger and dilute surficial bubbles,resulting in lower capacitive resistance and a higher frequency of the maximum phase angle.Optimized pores allowed released bubbles to easily merge and grow.The merged bubbles were quickly exhausted from the porous structure due to buoyancy.The gradient porous structure exhibited enhanced gas-liquid mass transfer,reducing resistance from bubbles and lowering the overpotential of hydrogen evolution reaction(HER).Specifically,gradient porous samples required an overpotential of 406 mV to drive 10 mA·cm-2 HER,while samples without gradient pores faced limited gas-liquid mass transfer,resulting a high bubble resistance and the overpotential as high as 766 mV to drive 10 mA·cm-2 HER.Moreover,the introduction of a gradient porous structure significantly improved the HER kinetics of Ni electrodes,with a Tafel slope as low as 129 mV·dec-1 for gradient samples compared to uniform porous samples(168 mV·dec-1 and 211 mV·dec-1).However,the consistent use of the same materials across all samples maintained the HER mechanism,confirming a Volmer step-controlled HER with Tafel slopes exceeding 120 mV·dec-1 for all samples.In conclusion,the application of a gradient porous structure can effectively reduce the HER overpotential of Ni electrodes and enhances their HER performance.
alkaline water electrolysisselective laser meltinggradient porous structurepore sizeelectrolyzing performancehydrogen evolution performancehydrogen evolution kineticsmass transfer between liquid and gas phase
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