Li, Tao Kim, Minkyu Liang, Zhu Asthagiri, Aravind Weaver, Jason F. Hydrogen oxidation on oxygen-rich IrO<sub>2</sub>(110) <p>We investigated the adsorption and oxidation of H<sub>2</sub> on O-rich IrO<sub>2</sub>(110) using temperature programmed reaction spectroscopy (TPRS) and density functional theory (DFT) calculations. Our results show that H<sub>2</sub> dissociation occurs efficiently on O-rich IrO<sub>2</sub>(110) at low temperature and initiates from an adsorbed H<sub>2</sub> σ-complex on the coordinatively-unsaturated Ir atoms (Ir<sub>cus</sub>). We find that on-top oxygen atoms (O<sub>ot</sub>), adsorbed on the Ir<sub>cus</sub> sites, promote the desorption-limited evolution of H<sub>2</sub>O during subsequent oxidation of the adsorbed hydrogen on IrO<sub>2</sub>(110) while suppressing reaction-limited production of H<sub>2</sub>O via the recombination of bridging HO groups (HO<sub>br</sub>) (~500 to 750 K) during TPRS. The desorption-limited TPRS peak of H<sub>2</sub>O shifts from ~490 to 550 K with increasing O<sub>ot</sub> coverage, demonstrating that O<sub>ot</sub> atoms stabilize adsorbed OH and H<sub>2</sub>O species. DFT predicts that molecularly-adsorbed H<sub>2</sub> dissociates on O-rich IrO<sub>2</sub>(110) at low temperature and that the resulting H-atoms redistribute to produce a mixture of HO<sub>br</sub> and HO<sub>ot</sub> groups, with equilibrium favouring HO<sub>ot</sub> groups. Our calculations further predict that subsequent H<sub>2</sub>O evolution occurs through the recombination of HO<sub>br</sub>/HO<sub>ot</sub> and HO<sub>ot</sub>/HO<sub>ot</sub> pairs, and that these reactions represent desorption-limited pathways because the dissociative chemisorption of H<sub>2</sub>O is favoured over molecular adsorption on IrO<sub>2</sub>(110). The higher stability of HO<sub>ot</sub> groups and their preferred formation causes the higher-barrier HO<sub>ot</sub>/HO<sub>ot</sub> recombination reaction to become the dominant pathway for H<sub>2</sub>O formation with increasing O<sub>ot</sub> coverage, consistent with the experimentally-observed upshift in the H<sub>2</sub>O TPRS peak temperature.</p> Hydrogen oxidation;IrO2;iridium oxide;dissociative chemisorption;water desorption;sigma complex 2019-01-31
    https://tandf.figshare.com/articles/journal_contribution/Hydrogen_oxidation_on_oxygen-rich_IrO_sub_2_sub_110_/7655582
10.6084/m9.figshare.7655582.v1