Morphology-Dependent α-Fe ₂ O ₃ Nanostructures as Bifunctional Electrocatalysts for Efficient Overall Water Splitting

Developing effective and inexpensive electrocatalysts that are composed of earth-abundant materials is an important approach for accelerating both the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), which together enable overall water splitting. In this context, α-Fe2O3 nanostructures with five distinct morphologiesnanoplates, nanospheres, rhombohedral, hexagonal bipyramids, and nanocubeswere synthesized through a controlled solvothermal process and characterized using XRD, HRTEM, SAED, and XPS. Electrocatalytic performance for all the morphologies toward HER and OER was systematically evaluated to assess the impact of morphological variation and specific exposed facets on catalytic activity. Among the synthesized morphologies, nanoplates and nanospheres, which expose low-index facets including the (012) plane as indicated by HRTEM and SAED analysis, exhibited the highest catalytic activity. The nanoplate morphology showed significantly better OER activity, requiring an overpotential of only 70 mV to reach 10 mA cm−2, along with a lower Tafel slope of 73.9 mV·dec−1, indicating faster reaction kinetics, while nanospheres achieved an overpotential of 88 mV at 10 mA cm−2 and a Tafel slope of 116 mV·dec−1 for HER. The detailed theoretical aspects were further evaluated by hydrogen adsorption free energy and OH* intermediate consideration. These results clearly showed that catalytic performance is strongly influenced by morphology and the surface structural characteristics of the different nanostructures.