ALD of Ultrathin Ternary Oxide Electrocatalysts for Water Splitting

Abstract

Semiconducting oxides, particularly mixtures of different transition-metal oxides, are promising materials for oxygen evolution reaction (OER) catalysts. Assessment of these materials is often complicated by inadequate dispersion of the materials, charge transport limitations, and lack of surface area characterization. Thin films deposited by atomic layer deposition (ALD) present an excellent way to overcome these issues. Here, we present the first work using ALD to investigate ternary oxide electrocatalysts, specifically with the Ti–Mn ternary oxide system. Thin-film mixtures of between 1.4 and 2.8 nm in thickness are successfully synthesized by ALD and show a high degree of mixing. At compositions between ∼10 and 70% Mn:(Mn+Ti), there is a reduction in ALD growth rate relative to the growth rates of the binary constituents. Moreover, we observe a shift in the chemical binding energies of both Mn and Ti over this composition range. An elevation in the activity of Mn active sites for OER is observed with increasing MnOx content in TiO2, increasing the turnover frequency (TOF) by approximately an order of magnitude. These results are consistent with previous DFT calculations. We also explore the effect of film thickness of the ternary metal oxide on catalytic activity, highlighting how ALD allows for charge transport limitations to be minimized.