Enhanced water oxidation reaction activity of Mn3O4 nanocrystals in an alkaline medium by doping transition-metal ions

Designing low-cost, Earth-abundant, and non-precious catalysts for electrochemical water oxidation reactions is particularly important for accelerating the development of sustainable energy sources and, further, can be fed to fuel cells. In the present work, we report the oxygen evolution reaction (OER) activity of a metal-oxide catalyst, Mn3O4, and study the effect of transition metal doping (Cu and Fe) on the OER activity of Mn3O4 in an alkaline medium. The Mn3O4 and transition metal (Cu and Fe) doped Mn3O4 catalysts were prepared using a hydrothermal reaction technique. Powder x-ray diffraction studies revealed that these compounds adopt a tetragonal spinel structure with an I4(1)/amd space group, and this is further supported with Fourier transform infrared spectroscopic measurements. These results are further supported by high-resolution transmission electron microscopic measurements. The electrochemical measurements of these catalysts reveal that the transition metal (Cu and Fe) doped Mn3O4 catalysts show better OER activity than pristine Mn3O4 (MO). The transition metal (Cu and Fe) doped Mn3O4 catalysts exhibit lower overpotential for the OER (eta (MCO) = 300 mV and eta (MFO) = 240 mV) than the MO (eta (MO) = 350 mV) catalyst. The better performance of Fe-doped Mn3O4 is further supported by turnover frequency calculations.