A Proof-of-Principle Demonstration: Exploring the Effect of Anode Layer Microstructure on the Alkaline Oxygen Evolution Reaction

This study explores the effect of Ni-Co-O anode layer microstructure on the oxygen evolution reaction (OER). Four anodes with similar Ni-Co-O loadings and chemical characteristics but distinct morphologies are fabricated by ultrasonic spraying catalyst inks of varying solvent composition (pure water vs a water-ethanol mixture) and drying temperatures (50 °C and 150 °C) on Ni plates. Upon varying solvent composition, particles in the water-based ink exhibited lower stability than particles in the water-ethanol-based ink, boosting the particle connectivity in the layers. This particle connectivity correlated with the mechanical strength of the layers, resulting in reduced contact resistance and enhanced activity. Our second observation is that at 50 °C, the surface morphology exhibited hill-like islands with higher roughness, while at 150 °C, concave hemispherical shapes with lower roughness were observed. From 2D-distribution data, we found that surface roughness correlated with the wettability with electrolyte. Roughness increased the lyophobicity and enhanced the activity through more accessible active sites and efficient bubble transport. Taken together, this work highlights how microstructure affects macroscopic layer properties, and how these in turn can enhance or diminish the performance of the OER compared to bare nickel, offering insights into the knowledge-based design of anode layers.