The oxygen evolution reaction (OER), in which water is oxidized to molecular oxygen, is an important part of many technologies including the photoelectrochemical splitting of water. There is much interest in the development of earth-abundant, affordable electrocatalysts for OER.  In this talk, we describe the use of atomic layer deposition (ALD) to deposit highly active manganese oxide (MnOx) catalysts for OER.  ALD is a vapor phase deposition technique capable of forming highly uniform conformal thin films with a fine control over film thickness and film composition.  It is becoming an attractive method for synthesizing catalytic thin films, opening new avenues for advanced catalytic designs.  We synthesize MnOx-based catalysts on glassy carbon supports using ALD and test them in both the OER and oxygen reduction reaction (ORR).  The catalysts are characterized using a variety of techniques and their activity is measured by cyclic voltammetry.  The ALD process produces Mn(II)O, which can be changed to higher oxidation states by annealing.  The as-deposited MnO catalyst is inactive for ORR, but highly active for OER.  Annealing the film to form Mn2O3 generates a catalyst that is active for both the OER and the ORR, approaching the activity of the most active MnOx catalysts known. Because ALD provides excellent control over film thickness, we show that the activity of the MnOx depends on the film thickness at the nanoscale.  This effect is explored using other metal oxide films for comparison, and the results indicate that beyond a critical thickness, charge transport limitations begin to reduce the activity of the films.  We discuss further implications of electrocatalyst design using ALD, including applications to photoelectrochemical water splitting.

Manganese oxide oxygen evolution catalysts deposited by ALD

247th National Meeting (2014)

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