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Polypyrrole films doped with Cl, SO and 4-toluene sulfonic ions (PPy/Cl, PPy/SO, PPy/Ts) with different polymerization charges were prepared by electrochemical polymerization. PPy/Ts films exhibited good electrochemical properties when their polymerization charges were 0.5 C cm and 1 C cm. However, PPy/Cl and PPy/SO films exhibited markedly larger specific capacitance than those of PPy/Ts films when their polymerization charges increased to 2 C cm or 4 C cm. A simple model was suggested for explaining the relation between the electrochemical properties and thickness of the PPy films. According to the model, the incremental polymerization bulk of PPy/Ts films from 1 C cm to 2 C cm is "inactive", which resulted in the reduction of the specific capacitance by half. X-ray diffraction patterns indicated that PPy/Ts films possessed a more ordered structure, which limited ion diffusion in the PPy matrix. Therefore, the high crystallinity of the PPy film does not always mean good capacitance properties. In the cycle stability test, the PPy/Ts film exhibited better stability, which should be closely related to its more ordered structure. It is noteworthy that we present a newly developed method to estimate the appropriate thickness of electrode materials, which is significant in the preparation of energy-storage devices.

We used direct-rate measurements and reflection absorption infrared spectroscopy (RAIRS) to investigate CO oxidation on a PdO(101) film at 450 K and focused on characterizing how the gas-phase composition (O 2 + CO) influences the reaction kinetics and the coupling between the reaction and the surface phases that develop. We find that chemisorbed O atoms on Pd(111) are intrinsically more reactive than PdO(101) and that CO oxidation rates can be as much as 2−3 times higher on Pd(111) compared with PdO(101) for the conditions studied. Using RAIRS, we show that reduction of PdO( 101) by CO produces metallic Pd(111) domains at 450 K and identified several rate processes that couple the PdO(101) and Pd(111) phases during reaction, including the formation of Pd( 111) domains from O vacancies on PdO(101), oxygen transfer from the oxide to the metal to generate chemisorbed O atoms, and the healing of surface oxygen vacancies on PdO(101) via O atom migration from the bulk oxide as well as O 2 dissociative adsorption. We show that the CO oxidation rates increase autocatalytically as the surface fraction of metallic Pd initially increases during reaction because Pd( 111) is more reactive than PdO(101) over the range of conditions studied. Our results further demonstrate that the oxide and gaseous O 2 can act cooperatively to supply metallic Pd(111) domains with chemisorbed O atoms, resulting in higher CO oxidation rates achieved on mixtures of PdO(101) and Pd(111) compared with pure Pd(111). The present study clarifies key rate processes and the resulting kinetic couplings among the gas-phase and solid phases during CO oxidation on partially reduced PdO(101). We expect that our findings will provide useful guidance for advancing first-principles kinetic modeling of CO oxidation promoted by transition-metal catalysts.

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