Unraveling the mechanism of enhanced oxygen evolution reaction using NiO_x@Fe₃O₄ decorated on surface-modified carbon nanotubes

Advanced core@shell structures have emerged as an important strategy for enhancing performance and introducing novel functionalities across diverse scientific and engineering domains, facilitated by synergistic interactions between the core and shell. Particularly, when core@shell electrocatalysts are applied to the oxygen evolution reaction (OER) in alkaline water splitting, they are promising for improving OER kinetics using economically feasible and readily available compounds, previously overlooked as electrocatalysts. As a representative study to demonstrate the synergistic effect of the core@shell structure on OER performance, we have developed a NiO_x@Fe₃O₄ structure decorated on surface-modified carbon nanotubes. Experimental results exhibit outstanding OER performance, including an overpotential (η₁₀) of 286 mV, a Tafel slope of 32 mV dec⁻¹, and a faradaic efficiency of 97.2% during an 18-hour chronoamperometry test. Remarkably, this performance surpasses that of Fe₃O₄ catalysts (η₁₀: 1266 mV, Tafel plot slope: 246.2 mV dec⁻¹). Also, computational simulations reveal that the electronic structure modifications in NiO_x@Fe₃O₄ promote electron transfer while significantly reducing the reaction energy barrier for boosting OER performance. This study offers scientific insights into the rational design of core@shell structures for enhanced OER performance, which have remained relatively unexplored.