Nickel foam thickness effect on alkaline electrolysis performance: Structural advantages outweighing transient ultrasonic activation

This study examines nickel foam thickness influence (1 mm and 2 mm, 110 PPI) on alkaline water electrolysis performance in 30 wt% KOH at 25 °C, specifically analyzing a short 20 s ultrasonic pulse at 26 kHz. A smooth stainless-steel electrode served as a non-porous reference to decouple the effects of porosity from acoustic activation. Polarization curves, current density gains, overpotential reduction, and high-speed imaging of bubble dynamics were analyzed under silent and transient ultrasonic conditions. Results show that the porous nickel foam structures promote efficient bubble detachment, leading to higher current densities and volumetric hydrogen production rates compared to the smooth stainless-steel reference. The 2 mm foam consistently outperformed the 1 mm foam, mainly associated with its higher areal density. Transient ultrasound produced modest improvements on the foam electrodes (2.3 mV average overpotential reduction; ≤ 3.7 % current density gain), whereas the smooth stainless-steel electrode exhibited a pronounced response (∼4.5 % current increase), consistent with surface gas film removal. The findings indicate that for high-porosity nickel foams (110 PPI), structural optimization—particularly increased thickness—provides greater performance benefits than short-duration ultrasonic activation under the conditions studied, with the latter appearing more effective on non-porous surfaces.