Importance of Interfacial Band Structure between the Substrate and Mn₃O₄ Nanocatalysts during Electrochemical Water Oxidation

The charge transport in the film-type electrocatalysts for the oxygen evolution reaction is a significant factor affecting the overall catalytic performance. For instance, transition metal oxide-based catalysts film has an optimum coating thickness due to the charge transport limitation. In this article, we investigated the charge transport behavior at the interface between the catalysts and the underlying substrate, which has been less investigated than the two other charge-transporting interfaces, that is, the catalysts surfaces and the inner catalysts film. We observed that Mn₃O₄ nanocatalysts exhibited different oxygen-evolving performances depending on the underlying substrate, and this activity trend was correlated with the work function of the substrate. We analyzed the work function dependency based on the energy band structure at the catalysts-substrate interface and determined that the substrates with low work functions formed high Schottky barriers, disturbing the interfacial charge transport. On the basis of this understanding, we demonstrated that the catalytic activity of Mn₃O₄ nanocatalysts film can be significantly enhanced using industrially important Ti substrates that have a thin buffering interlayer with the proper work function.