Morphology-Driven Enhancement of Alkaline OER Performance in Spinel NiCo2O4 Nanosheet Electrodes

Abstract

The oxygen evolution reaction (OER) is a critical anodic process in alkaline water electrolysis, and its catalytic performance can be effectively regulated through rational morphology engineering that governs active-site exposure, mass transport, and charge-transfer kinetics. Herein, we report a precursor-controlled synthesis of spinel NiCo2O4 (NCO) catalysts with tunable two-dimensional architectures for efficient alkaline OER. By employing hexamethylenetetramine (H) and urea (U) as precipitating agents, the NiCo2O4 catalysts with distinctly different nanosheet morphologies were directly grown on nickel foam. The NCO-H catalyst exhibits substantially enhanced OER activity by achieving lower overpotential of 259 mV, a smaller Tafel slope of 84 mV dec(-1), and higher turnover frequency compared to NCO-U catalyst. The superior OER performance is attributed to an ultrathin, highly interconnected nanosheet network that provides abundant accessible active sites, shortened ion-diffusion pathways, and accelerated interfacial charge transfer. Moreover, the optimized electrode demonstrates excellent durability (50 h) with negligible potential degradation after the partial surface transformation into an oxyhydroxide-rich active phase, while post-stability polarization and impedance analyses confirm the preservation of catalytic integrity. These findings highlight precursor-regulated morphology engineering as an effective strategy for optimizing the electrocatalytic performance of spinel oxides and establish NiCo2O4 as a robust, earth-abundant OER catalyst for alkaline water-splitting applications.