Abstract:

During the process of electrolyzing water to produce hydrogen, the pores in the porous electrode will be blocked by bubbles, which will hinder gas diffusion and the flow of electrolyte in the porous electrode, resulting in an increase in the mass transfer resistance of the electrode. This in turn affects the rate and energy consumption of hydrogen production through electrolysis of water. Three regular shaped diffusion layers of nickel-iron alloy electrodes, LSL-PTL, MMM-PTL and SLS-PTL, were fabricated by 3D metal printing and visualized for water electrolysis experiments. In the experiments, the changes of gas-liquid two-phase flow in the gradient porous transport layer at different current densities were quantitatively recorded, including parameters such as bubble morphology, pore gas content and bubble detachment rate. The effects of the gradient of the diffusion layer on the gas-liquid mass transfer process were investigated, and the effects of different electrode gradient structures on the impedance and overpotential during electrolysis were analyzed. The experimental results show that compared with the two gradient structures of SLS-PTL and MMM-PTL, the gradient structure of LSL-PTL, i.e., gradually increasing the pore size from the catalytic layer, always maintains a lower volumetric gas content. It can accelerate the migration of gas bubbles in the diffusion layer, make the gas-liquid exchange more frequent, and effectively reduce the gas-liquid mass transfer resistance. Moreover, a lower mass transfer impedance and electrolytic overpotential can be obtained by using the diffusion layer with this gradient, and the relationship of electrolytic potentials of the three gradient electrodes at the same current density is . Therefore, a diffusion layer with LSL-PTL gradient in water electrolysis can improve the hydrogen production efficiency and reduce the energy loss. This study provides an intuitive basis for the active control of the gas-liquid mass transfer process in water electrolysis for hydrogen production and the structural design of the porous transport layer in the electrolytic cell, which will have a positive impact on the further development of electrolytic water hydrogen production technology.

Key words: water electrolysis, porous transport layer, gradient structure, hydrogen production, gas-liquid flow

摘要：

在电解水制氢的过程中，多孔电极内的孔隙会发生气泡阻塞现象，这会妨碍气体扩散以及电解液在多孔电极内的流动，从而导致电极传质电阻的增加，进而影响电解水制氢的速率和能耗。采用3D金属打印技术制备了LSL-PTL、MMM-PTL和SLS-PTL三种规则的镍铁合金电极扩散层，进行了可视化的水电解实验，定量地记录了不同电流密度下梯度多孔传输层中气液两相流动的变化，包括气泡形态、孔隙含气率和气泡脱离速率等参数，研究扩散层梯度对气液传质过程的影响，并分析了不同电极梯度结构对电解过程中阻抗和过电位的影响。实验结果显示，与SLS-PTL和MMM-PTL相比，LSL-PTL的梯度结构从催化层即逐渐增大孔隙尺寸，始终保持较低的容积含气率，可以加速气泡在扩散层中的迁移，使气液交换更加频繁，有效减小气液传质阻力，并获得更低的传质阻抗和电解过电位，三种梯度电极在相同电流密度下的电解电势关系为。因此，在水电解中采用LSL-PTL梯度的扩散层可以提高制氢效率，减少能耗损失。这项研究为水电解制氢中气液传质过程的主动控制和电解池多孔传输层的结构设计提供了直观依据，对电解水制氢技术的进一步发展具有积极推动作用。

关键词: 水电解, 多孔传输层, 梯度结构, 制氢, 气液两相流