激光选区熔化制备梯度多孔镍电极及其电解水制氢性能

Fabrication of Gradient Porous Ni Electrodes by Selective Laser Melting and Their Performance in Water Electrolysis for Hydrogen Production

摘要:

镍是目前应用最广泛的碱式电解水制氢电极材料之一。对镍电极进行多孔化处理，可有效提高其析氢效率并降低制氢能耗。然而，现有报道仅研究了孔隙率、平均孔径等对电极析氢性能的影响，缺乏针对梯度多孔电极孔隙尺寸和分布等影响的研究。为此，设计了4组具有不同孔隙尺寸和排布方式的多孔电极模型，并且采用激光选区熔化技术制备高精度成型电极样品，表征了样品的表面形貌、截面微观组织、电化学性能及稳定性，深入分析和研究了样品的析氢性能。结果表明，4组样品均呈现出粗糙微观表面，为析氢反应提供更多的活性位点。所有样品均表现出优异的电解稳定性，经测试后未见明显的性能衰减。梯度多孔结构有利于气液传质，减小气泡层电阻，降低析氢过电位。当电流密度为10 mA?cm^-2时，梯度多孔样品的析氢过电位虽仅为406 mV，但气液传质效果较差，而气泡层电阻较大的均匀多孔样品的析氢过电位却高达766 mV。梯度多孔结构的构筑可显著提高镍电极的析氢动力学特性，梯度多孔样品的Tafel斜率最低为129 mV?dec^-1，明显低于均匀多孔电极的Tafel斜率168和211 mV?dec^-1。析氢过程受Volmer步骤控制，尽管镍电极析氢动力学特性得到提升，但并未改变镍电极的析氢机理，所有样品的Tafel斜率均高于120 mV?dec^-1。因此，引入梯度多孔结构可有效降低镍电极材料的析氢过电位，提升析氢性能。本研究为镍电极的结构优化设计及析氢性能的提升，提供了新思路。

Abstract:

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.