Nickel-Doping Effect on Mn3O4 Nanoparticles for Electrochemical Water Oxidation under Neutral Condition

Abstract

As the demand for energy has dramatically increased in the past decade, electrochemical water splitting has been regarded as an attractive approach to produce renewable hydrogen energy. However, large overpotentials of oxygen-evolving reaction (OER) is a key bottleneck for practical application. Thus, water-oxidizing electrocatalysts with low cost and high efficiency should be developed. Here, 5 nm-sized Mn3O4 nanoparticles (NPs) are synthesized by a hydrothermal method, which is appropriate for large-scale production. To further improve their performance, various 3d transition metal elements are successfully doped in Mn3O4 NPs. Ni-doped Mn3O4 NPs exhibit the highest efficiency among the Mn3O4 NPs doped with various elements. Based on structural analysis, the Ni-doping process leads to the lattice distortion of their tetragonal spinel structure and it strongly correlates with the enhancement of OER activity. The overpotential at the current density of 10 mA cm(-2) is 524 and 458 mV for pristine and 5 at% doped Mn3O4 NPs under neutral condition. The heteroatom-doping process in sub-10 nm-sized nanocatalysts is expected to be a promising methodology to induce distorted structure related to active species. Thus, it can be effective to improve catalytic performance of various heterogeneous nano-catalysts.