Experimental study of gas-liquid flow visualization in gradient porous transport layers based on hydrogen production by water electrolysis

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 ELSL < EMMM < ESLS. 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. © 2024 Materials China. All rights reserved.