Redox-active transition metal oxides are complex non-stoichiometric materials. Their ability to cycle between different oxidation states is key to many of their applications in catalysis, electrocatalysis, solar energy conversion, electrochromic materials, etc. Changes in the metal oxidation state require a compensating change in the stoichiometry of the material. At high temperatures, the formation of oxygen atom vacancies compensate the reduction of metal cations results in nonstoichiometric material compositions such as CeO2–x. At ambient temperatures, however, there is evidence that reduction of metal ions is charge-balanced by the addition of interstitial or surface hydrogen. Although observing the H spectroscopically is challenging, studies from our laboratory on ZnO(H)x, TiO2(H)x and CeO2–x(H)y, show that this hydrogen is chemically reactive. These reactions show the varying hydrogen affinities of the metal oxide nanocrystals. The development of a thermochemical hydrogen affinity scale will be discussed, including the challenges involved and connections with other hydrogen-transfer materials.

Towards a thermochemical hydrogen-affinity scale for oxide materials, and its implications in reactivity and catalysis

253rd National Meeting (2017)

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