Iron doping of nickel oxide films results in enhanced activity for promoting the oxygen evolution reaction (OER). Whereas this enhanced activity has been ascribed to a unique iron site within the nickel oxide matrix, we show here that Fe doping influences the Ni valency. The percent of Fe^3+ doping promotes the formation of formal Ni^4+, which in turn directly correlates with an enhanced activity of the catalyst in promoting OER. The role of Fe^3+ is consistent with its behavior as a superior Lewis acid.
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