Understanding how materials that catalyze the oxygen evolution reaction (OER) function is essential for the development of efficient energy storage technologies. Traditional understanding of the OER mechanism on metal oxides involves four concerted proton–electron transfer steps on metal-ion centers at their surface, and product oxygen atoms derived from water. Here, using in situ 18O isotope labeling mass spectrometry, we provide direct experimental evidence that the O2 generated during the OER on some highly active oxides can come from lattice oxygen. The oxides capable of lattice-oxygen oxidation also exhibit pH-dependent OER activity on the reversible hydrogen electrode scale, indicating non-concerted proton–electron transfers in the OER mechanism. Based on our experimental data and density functional theory calculations, we discuss fundamentally different mechanisms from the conventional scheme and show that increasing the covalency of metal–oxygen bonds is critical to trigger lattice-oxygen oxidation and enable non-concerted proton–electron transfers during OER.

Design principles of oxides to catalyze oxygen evolution reaction

253rd National Meeting (2017)

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