Wetting Across the Lyophilic–Lyophobic Spectrum: Morphological Tuning of Anode Catalyst Layers for the Alkaline Oxygen Evolution Reaction

Abstract

In alkaline water electrolysis (AWE), anode wettability plays a critical role in governing bubble dynamics at the anode–electrolyte interface. Effective bubble management is essential for improving AWE performance, as it enhances active site accessibility and reduces transport resistance. This study investigates the influence of super-lyophilicity and super-lyophobicity of spray-coated nickel iron layered double hydroxide (Ni-Fe-LDH) anodes on the electrochemical performance for the oxygen evolution reaction (OER). Surface wettability is adjusted through binder selection (Sustainion and Nafion) and drying-induced morphological modifications. Sustainion-based anode layers display pronounced super-lyophilicity (θ < 10 °) governed by the Wenzel model. In contrast, Nafion-based films exhibit tailored super-lyophobicity (θ > 150 °), indicative of a Cassie–Baxter-type wetting state. The super-lyophilic anodes achieve the lowest overpotential, with a reduction of 73 mV at 100 mA cm^-2 compared to the super-lyophobic anode. Post-electrochemical analysis reveals a correlation between wetting states and the extent of the anode’s active area utilization. Super-lyophilic anodes achieve a complete wetting and full layer contribution, while super-lyophobic anodes exhibit large non-wetted regions as high as ~ 47 %, resulting in partial contribution to the OER. The understanding gained by this work enables rational design of high-performance anodes through systematic control of wettability.