Operando Near Ambient Pressure XPS (NAP-XPS) Study of the Pt Electrochemical Oxidation in H2O and H2O/O2 Ambients
2016
Saveleva, Viktoriia A. | Papaefthimiou, Vasiliki | Daletou, Maria K. | Doh, Won H. | Ulhaq-Bouillet, Corinne | Diebold, Morgane | Zafeiratos, Spyridon | Savinova, Elena R.
Oxides on the surface of Pt electrodes are largely responsible for the loss of their electrocatalytic activity in the oxygen reduction and oxygen evolution reactions. In this work we apply near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study in operando the electrooxidation of a nanoparticulated Pt electrode integrated in a membrane-electrode assembly of a high temperature proton-exchange membrane under water and water/oxygen ambient. Three types of surface oxides/hydroxides gradually develop on the Pt surface depending on the applied potential at +0.9, + 2.5, and +3.7 eV relative to the 4f peak of metal Pt and were attributed to the formation of adsorbed O/OH, PtO, and PtO₂, respectively. The presence of O₂ in the gas-phase results in the increase of the extent of surface oxidation, and in the growth of the contribution of the PtO₂ oxide. Depth profiling studies, in conjunction with quantitative simulations, allowed us to propose a tentative mechanism of the Pt oxidation at high anodic polarization, consisting of adsorption of O/OH followed by nucleation of PtO/PtO₂ oxides and their subsequent three-dimensional growth.
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