Water splitting into oxygen, protons and electrons is central to the generation of sustainable energy carriers that can replace fossil fuels. Despite intensive studies, the mechanism of the anodic process during electrochemical water splitting � the Oxygen Evolution Reaction (OER) � remains poorly understood. In this work, we focus on the OER catalyzed by �-MnO2. We analyze reactivity at the 2 x 1 (110) �-MnO2 surface as described by Density Functional Theory (DFT), with emphasis on the influence of O/OH coverage (which corresponds to different �-MnO2 phases as a function of pH). We find that the rate-determining step of OER switches at pH 12-13 consistently with the observation of changes in the slope of the experimental Tafel plots. The comparative analysis of the OER mechanism catalyzed by RuO2 � a highly effective OER catalyst, provides fundamental insights into structure/function relations in the two catalytic surfaces. In particular, the preferential spin state of terminal oxo/oxyl species is found to be critical during O-O bond formation, upon interaction with substrate water. We find that �-MnO2 tends to form inactive oxo species on bridge sites for stoichiometric MnO2 as well as for MnO2 with oxygen vacancies while active oxyl species are formed on the (110) �-MnO2 surface upon surface doping with Fe or Ru atoms. Our findings are particularly relevant to the design of highly active catalytic surfaces for OER based on inexpensive earth-abundant materials.

Mechanistic studies of water oxidation catalyzed by the �-MnO<sub>2</sub> (110) surface

247th National Meeting (2014)

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Mechanistic studies of water oxidation catalyzed by the �-MnO2 (110) surface

Mechanistic studies of water oxidation catalyzed by the �-MnO₂ (110) surface