Enhanced bifunctional water electrolysis performance of spherical ZnMn₂O₄ nanoparticles

Spinel-type transition metal oxide-based catalysts are crucial for efficient electrocatalytic oxygen and hydrogen generation. Therefore, in this study, zinc manganite (ZnMn₂O₄) nanostructures were synthesized using two different reducing agents, including sodium carbonate (Na₂CO₃) and sodium hydroxide (NaOH), through the coprecipitation method. When ZnMn₂O₄ was synthesized using NaOH, the sample exhibited a morphology with the aggregated and stacked nanobundles. In contrast, the Na₂CO₃-derived ZnMn₂O₄ sample demonstrated an interconnected and agglomerated spherical nanoparticle structure. For the oxygen evolution reaction, the spherical ZnMn₂O₄ nanoparticles exhibited the exceptional electrocatalytic performances, with an overpotential of 110 mV and a low Tafel slope of 47 mV/dec, showing excellent durability at 10 mA/cm² in an alkaline electrolyte. For the hydrogen evolution reaction, the spherical ZnMn₂O₄ nanoparticles indicated a low overpotential of 158 mV and a Tafel slope of 120 mV/dec, with excellent stability at −10 mA/cm². These findings suggest that the spherical ZnMn₂O₄ nanoparticles are effective electrocatalysts for highly efficient water-splitting.