Mechanochemical activation of nickel oxide: a pivotal step in the process chain enabling binder-free-anodes for alkaline water electrolysis

Sustainable hydrogen production via alkaline water electrolysis (AWE) demands robust electrocatalysts for the oxygen evolution reaction (OER) that combine performance with scalability. Herein, we address critical challenges in AWE by mechanochemical activation of nickel oxide (NiO), enabling the fabrication of binder-free anodes. First, we investigated the effects of planetary ball milling on NiO, which include a decrease in crystallite size, increase in specific surface area, elevated Ni3+ content, and enhanced surface hydroxyl concentration. Milling with larger beads induced more pronounced structural transformations due to higher impact forces. Electrochemical testing revealed an improved overpotential of the mechanochemically activated NiO compared to the bare Ni plate substrate (365 mV vs. 377 mV at 100 mA cm-2 in 1 M KOH), with excellent particle-particle cohesion enabling mechanically stable, binder-free anodes. Post-OER analysis using X-ray photoelectron spectroscopy identified hydroxyl-mediated cohesion and adhesion as key factors for mechanical integrity and performance. Building on these insights, we translated the approach to scalable stirred media milling, which enables direct ink formulation. Milling in isopropanol suppressed reagglomeration and eliminated the need for an intermediate drying step. The resulting NiO exhibited even lower overpotential (343 mV) and high mechanical robustness, offering a streamlined, binder-free strategy for OER electrode fabrication.