Intrinsic Alkaline OER Activity in Mechanochemically Activated WO3 from Commercial and Single-Crystal Precursors

This study uncovers the interplay between phase-induced interfaces and mechanochemical activation on the alkaline oxygen evolution reaction (OER) performance of tungsten oxide (WO3). Commercial polycrystalline (WO3-C) and synthesized single-crystal (WO3-S) monoclinic WO3 precursors were subjected to identical mechanochemical processing by planetary ball milling (PBM). Ball-milled single-crystal WO3 (WO3-S-PBM) yielded nanocrystalline powders (~20-50 nm) with enriched γ-monoclinic phase content (40% vs. 28% for WO3-C-PBM), suppressed surface W⁵⁺ defects, and enhanced hydroxylation. Using Hansen solubility parameters, powders were formulated into stable inks to fabricate OER anodes on Ni substrates. Multi-technique characterization revealed that anodes made from WO3-S-PBM resulted in continuous, crack-free coatings with uniform nanoscale roughness (5-fold lower variability) and enhanced wettability (initial contact angle 40° vs. 82°), establishing dense WO3/Ni interfacial contacts that were not achievable for WO3-C-PBM. Electrochemically, WO3-S-PBM/Ni delivered a current density of 84.8 mA cm-2 at 1.65 V vs. RHE with 328 mV overpotential a 3-fold enhancement over WO3-C-PBM (375 mV) despite nearly identical active surface areas (