Paper TF+EN-WeM5
Ultra-thin transition Metal Oxide-titania Alloy Coatings for Water Oxidation by Atomic Layer Deposition

Wednesday, October 21, 2015, 9:20 am, Room 111

Synthesizing chemical fuels from solar energy requires a source of electrons. The most obvious choice for generating these electrons is the oxidation of water. The oxygen evolution reaction, however, is kinetically challenging, requiring significant overpotentials even with the best noble metal catalysts. At these positive potentials, preserving catalyst stability becomes a key concern. In industrial chlor-alkali electrolysis, which requires similarly positive potentials, the issue of catalyst durability was solved with the development of the dimensionally stable anode (DSA). Today’s DSAs consist of a mixed TiO₂/RuO₂ coating prepared by thermal decomposition of appropriate precursors on a Ti substrate (Over, H. Chem. Rev., 2012, 112, 3356). The TiO₂ imparts stability by preventing Ru dissolution, while the RuO₂ imparts sufficient activity and conductivity to the electrode. We report on the fabrication of an ultra-thin analogue to the DSA by atomic layer deposition (ALD) of ruthenium and TiO₂. We hypothesize that a conformal ALD coating of this type on nanostructured electrodes can optimize both the catalytic activity and durability for water oxidation while minimizing the use of transition metal components that have very limited Earth-abundance.

Both TiO₂ and Ru can be deposited simultaneously in our ALD reactor. Thus, by changing the relative number of ALD cycles for each precursor, we can achieve precise control of the catalyst content within the films. Preliminary results suggest that enhanced stability is achieved through the alloying process after annealing. The alloyed films also exhibit overpotentials that are competitive with pure ALD-Ru films deposited on a TiO₂ protective layer, even at relatively low Ru content. By decorating the TiO₂ surface with Ru ions at an optimal areal density, ALD alloying has the potential to achieve efficient catalysis of oxygen evolution from water while minimizing usage of the noble metal catalyst.