Combined studies of DFT atomistic modelling and in situ FTIR spectroscopy on surface oxidants and CO oxidation at Ru electrodes

Abstract

Combined studies of DFT atomistic modelling and in-situ FTIR spectroscopy on surface oxidants and CO oxidation at Ru electrodes, Journal of Electroanalytical Chemistry (2012), doi: http://dx.doi.org/10. 1016/j.jelechem.2012.10.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Combined studies of DFT atomistic modelling and in-situ ABSTRACTWe report the combined studies of density functional theory (DFT) calculations and electrochemical in-situ FTIR spectroscopy on surface oxidants and mechanisms of CO oxidation at the Ru(0001) electrodes. It is shown that CO can co-adsorb with both O and OH species at lower potential region where a low coverage of the (2 x 2)-O/OH adlayer formed; the oxidation of CO adsorbates takes place at higher potentials where a high coverage of the (1 x 1)-O/OH adlayer formed. Surface O species are not the active oxidants under all coverages studied, due to the high reaction barriers between CO and O (> 1 eV). However, surface OH species with higher coverage are identified as the active oxidants, and CO oxidation takes place via a two-steps' mechanism of CO + 3OH  COOH +2OH  CO 2 + H 2 O + OH, in which three nearby OH species are involved in the CO 2 formation: CO reacts with OH, forming COOH; COOH then transfers the H to a nearby OH to form H 2 O and CO 2 , at the same time, another H in the H 2 O transfers to a nearby OH to form a weak adsorbed H 2 O and a new OH. The reaction barrier of these processes is reduced significantly to around 0.50 eV. These new results not only provide an insight into surface active oxidants on Ru, which is directly relevant to fuel cell catalysis, but also reveals the extra complexity of catalytic reactions taking place at solid/liquid electrochemical interface in comparison to the relatively simpler ones at solid/gas phase.

An insight into methanol oxidation mechanisms on RuO2(100) under an aqueous environment by DFT calculations

“…However, at higher potentials, significant oxidation of methanol to CO 2 in acid solution and to bicarbonate and formate in alkaline solution, was observed, which was attributed to the formation of an active RuO 2 (100) phase on Ru(0001). [11][12][13][14][15] Wang et al also found that RuO 2 (100) was more active than Ru(0001) in CO oxidation. 16 In comparison with the most stable RuO 2 (110) surface, [17][18][19] the RuO 2 (100) with the higher surface energy was less investigated in the literature.…”

“…9,10 The electrochemical behavior of the Ru singlecrystal plane, and the chemistry of small organic molecules has been investigated. [11][12][13][14][15] The surface oxidation states, i.e., (2 Â 2)-O and (1 Â 1)-O were identified over a potential range on Ru(0001). [11][12][13][14][15] No oxidation of methanol is observed at potentials below 0.8 V, suggesting that the surface oxides block the Ru(0001) physically for methanol adsorption.…”

“…[11][12][13][14][15] The surface oxidation states, i.e., (2 Â 2)-O and (1 Â 1)-O were identified over a potential range on Ru(0001). [11][12][13][14][15] No oxidation of methanol is observed at potentials below 0.8 V, suggesting that the surface oxides block the Ru(0001) physically for methanol adsorption. However, at higher potentials, significant oxidation of methanol to CO 2 in acid solution and to bicarbonate and formate in alkaline solution, was observed, which was attributed to the formation of an active RuO 2 (100) phase on Ru(0001).…”

Insights into the Coadsorption and Reactivity of O and CO on Ru(0001) and Their Coverage Dependence

“…The adsorption energy of CO was found to be around 0.6 eV larger in the honeycomb structure. However, note that in both considered structures the O:CO ratio was 2:1, i.e., none of them corresponded to the low temperature CO saturation coverage (the one with crowded CO molecules in the empty space of the (2×1)-O layer) found experimentally by Kostov et al 17 Also the energetics and minimum energy path for CO oxidation have been studied for different adsorbate structures and coverages, including the p(2×2)-O+CO structure, [21][22][23] the p(2×1)-O with CO in hcp sites in a O:CO ratio of 2:1, 23,24 the 0.5 ML O honeycomb structure, 24,25 and two very low coverage phases consisting in one O and one CO in a 5×5 cell and three O and one CO in the same cell. 26 A general result of these studies was that the main responsible of the activation barrier that hinders CO oxidation at Ru(0001) in UHV conditions is the energy required to destabilize and move the atomic oxygen from its adsorption site.…”

EXAFS Peaks and TPR Characterizing Bimetallic Interactions: Effects of Impregnation Methods on the Structure of Pt-Ru/C Catalysts

“…Several explanations have been offered for the role of M 2nd in improving the catalytic performance: (1) it may change the morphology of Pt clusters and help anchor Pt and maintain it in a state of high dispersion [14,[20][21][22][23][24][25][26]; (2) it may convert the poisonous species into harmless compound in the reaction [2,27]; (3) in bonding with Pt, it may change the electronic properties and geometric features of Pt thereby decreasing the adsorption of poisonous species on Pt [18,24,[28][29][30][31][32][33]; and (4) in association with Pt, it may modify the catalytic properties of Pt [34][35][36][37][38]. To discriminate the role of M 2nd in improving the catalytic performances, it is crucial to determine the structure of the catalysts, specifically, the extent of bimetallic interaction.…”