Tailoring Structural Transformation in Murdochite Metal Oxide for Superior Water Oxidation Catalysis

Developing cost-effective, high-performance electrocatalysts from earth-abundant elements is essential for advancing sustainable hydrogen production via alkaline water electrolysis. The structural tunability and large surface areas of porous transition metal oxides make them very appealing, which enhances the catalytic water-oxidation (OER) kinetics. This research introduces a scalable and eco-friendly technique for producing porous ε-MnO 2 nanoparticles via the structural transformation of Murdochite-type Mg 6 MnO 8 (MMO) using dilute nitric acid. The optimized sample, treated with 1 M acid (AT-1M), shows a 10-fold increase in the surface area of 225 m 2 ·g –1 over pristine MMO resulting from selective Mg 2+ cation leaching. This structural reconfiguration improves surface roughness, porosity, and hydrophilicity while exposing abundant surface Mn 3+ /Mn 4+ active sites that facilitate oxygen intermediate adsorption, significantly enhancing electrocatalytic performance. The AT-1M sample outperforms the parent MMO with a decrease in the Tafel slope of 135 mV dec –1 and a lowering of the OER overpotential to 304 mV at 10 mA cm –2 . These findings establish acid-directed structural transformation as a versatile, environmentally benign approach for engineering high-performance nanostructured electrocatalysts made of earth-abundant metal oxide.