Using Atomic Layer Deposition to Create Mixed Metal Oxide Electrodes for H2O2 Generation through Water Oxidation

Abstract

The electrochemical synthesis of H2O2 through water oxidation provides a means of producing a useful chemical and potential fuel without the input of fossil fuels. Highly stable metal oxides like TiO2 and SnO2 surfaces have shown activity as electrocatalysts for oxidative H2O2 generation, but often require high overpotentials that result in parasitic side reactions. Using atomic layer deposition (ALD) to introduce well-distributed layers of MnOx dopant one can lower the required overpotential of TiO2 and SnO2 surfaces for H2O2 production. Even a single sub-surface layer of MnOx can alter the redox behavior of a 5 nm thick oxide film. While the doped films maintained reversible Mn redox peaks and prevent the total dissolution of the deposited Mn, in-situ inductively coupled mass spectrometry did reveal loss of Mn from the film at applied potentials close to the expected onset potential of the 2e- water oxidation reaction. The depth of sub-surface MnOx was varied to determine the effect on both electrode activity, selectivity, and stability. In addition, the use of either inert and oxidizing annealing atmospheres was used to control both the distribution and the charge-state of the Mn species. This work provides some indication of how manganese-doped metal oxide electrodes degrade during operation and how controlling the surface can improve the activity and stability of the device. This study may also provide a framework of how other redox active species can be embedded within more stable oxide matrices using ALD methods to maximize stability and activity.