Alkaline Water Electrolysis at 25 A cm-2 with a Microfibrous Flow-through Electrode

The generation of renewable electricity is variable, leading to periodic oversupply. Excess power can be converted to H-2 via water electrolysis, but the conversion cost is currently too high. One way to decrease the cost of electrolysis is to increase the maximum productivity of electrolyzers. This study investigates how nano- and microstructured porous electrodes can improve the productivity of H-2 generation in a zero-gap, flow-through alkaline water electrolyzer. Three nickel electrodes-foam, microfiber felt, and nanowire felt-are studied to examine the tradeoff between surface area and pore structure on the performance of alkaline electrolyzers. Although the nanowire felt with the highest surface area initially provides the highest performance, this performance quickly decreases as gas bubbles are trapped within the electrode. The open structure of the foam facilitates bubble removal, but its small surface area limits its maximum performance. The microfiber felt exhibits the best performance because it balances high surface area with the ability to remove bubbles. The microfiber felt maintains a maximum current density of 25 000 mA cm(-2) over 100 h without degradation, which corresponds to a hydrogen production rate 12.5- and 50-times greater than conventional proton-exchange membrane and alkaline electrolyzers, respectively.