Bubble dynamics matters at high-rate water electrolysis

Bubbles accumulation in the electrode limits anion exchange membrane water electrolyzer performance at industrial current densities (>1.0 A cm-2). Currently, conventional electrode designs prioritize the optimization of the electrochemically active surface area. However, this study reveals that bubble dynamics matters high-rate water electrolysis efficiency in anode-feeding mode in three ways:1) cover active sites at the anode; 2) hinder water diffusion through the membrane; 3) cause water shortage at the cathode. Based on this mechanism, we propose an easy-to-prepare gradient stainless steel square hole mesh electrode. It not only offers a low cost ($8-150/m2), but also improves bubble dynamics. As a result, it reduces the cell voltage by 0.14 V at a current density of 5.0 A cm-2, even with a lower electrochemically active surface area compared to the stainless steel felt electrode. And it maintains a stable operation over 400 hours. This work redefines electrode engineering paradigms, shifting focus from electrochemically active surface area-centric approaches to two-phase flow management in water electrolyzers for industrial current densities-scale hydrogen production. Efficient hydrogen production at industrial current densities is hindered by bubbles blocking water flow to electrodes in water electrolyzers. Here, the authors report a low-cost gradient mesh electrode that effectively manages bubble removal, ensuring stable and high-efficiency operation.