Analysis of the hydrogen evolution reaction at Ni micro-patterned electrodes

The behavior of bubbles generated by the hydrogen evolution reaction (HER) and the effect of these bubbles on HER performance were investigated using Ni micro-patterned electrodes. This study focused on the correlation between bubble behaviors affecting potential increase of HER and the surface microstructures of micro-patterned Ni cathode. Ni microdot array structures with diameters of approximately 5–10 μm, pitch of approximately 5–10 μm, and various dot heights were fabricated for alkaline water electrolysis measurements. The Ni micro-patterned structures controlled the surface wettability of the electrode. The change in the wettability influenced the HER efficiency during galvanostatic electrolysis at –20 mA cm^–2. Moreover, in situ observation of the evolved bubbles on the electrode surface revealed that bubbles with larger diameters evolved on the electrode surface with lower wettability, and bubbles tended to detach from the electrode surface by decreasing the contact area between the bubbles and the electrode. It was also observed that bubbles evolved more easily on the sidewall of Ni microdots and that generated bubbles moved onto the surface of the microdots in high-aspect Ni micro-patterned electrodes, indicating that an increase in the overpotential can be suppressed by different bubble nucleation behaviors. Therefore, the micro-patterned surface texture affected the bubble nucleation and growth behaviors, which would suppress the decrease in HER efficiency. These results can provide insights for fabricating highly efficient surfaces for HER catalytic electrodes.