The influence of methanol on the chemical state of PtRu anodes in a high temperature direct methanol fuel cell studied in situ by synchrotron based near ambient pressure x ray photoelectron spectroscopy

Synchrotron radiation based near ambient pressure x ray photoelectron spectroscopy NAP XPS has recently become a powerful tool for the investigation of interfacial phenomena in electrochemical power sources such as batteries and fuel cells. Here we present an in situ NAP XPS study of the anode of a high temperature direct methanol fuel cell with a phosphoric acid doped hydrocarbon membrane, which reveals an enhanced flooding of the Pt3Ru anode with phosphoric acid in the presence of methanol. An analysis of the electrode surface composition depending on the cell voltage and on the presence of methanol reveals the strong influence of the latter on the extent of Pt oxidation and on the transformation of Ru into Ru IV hydroxid

Potential induced segregation phenomena in bimetallic PtAu nanoparticles an in situ near ambient pressure photoelectron spectroscopy NAP XPS study

The surface properties of a model membrane electrode assembly of a high-temperature proton-exchange-membrane fuel cell with a nanostructured PtAu working electrode were studied under operando conditions (polarization, humidified H₂ atmosphere, 150 °C) using near-ambient-pressure photoelectron spectroscopy (NAP–XPS). NAP–XPS proved to be a powerful tool for the in situ investigation of the changes in the chemical composition, the segregation of the two metals, and the changes in their oxidation state. Nondestructive depth profiling revealed the influence of the polarization and the gas ambient on the distribution of the two metals in the near-surface region. The results suggest that the surface of the electrode is covered by a thin layer of gold, which is stable at potentials below the onset of surface-oxide formation. Anodic oxidation of the PtAu electrode pulls Pt to the surface, leading to intermixing of Pt and Au atoms and the formation of an interfacial allo

Uncovering the Stabilization Mechanism in Bimetallic Ruthenium Iridium Anodes for Proton Exchange Membrane Electrolyzers

Proton exchange membrane (PEM) electrolyzers are attracting an increasing attention as a promising technology for the renewable electricity storage. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is applied for in situ monitoring of the surface state of membrane electrode assemblies with RuO2 and bimetallic Ir0.7Ru0.3O2 anodes during water splitting. We demonstrate that Ir protects Ru from the formation of an unstable hydrous Ru(IV) oxide thereby rendering bimetallic Ru−Ir oxide electrodes with higher corrosion resistance. We further show that the water splitting occurs through a surface Ru(VIII) intermediate, and, contrary to common opinion, the presence of Ir does not hinder its formation

Operando Evidence for a Universal Oxygen Evolution Mechanism on Thermal and Electrochemical Iridium Oxides

Progress in the development of proton exchange membrane (PEM) water electrolysis technology requires decreasing the anode overpotential, where the sluggish multistep oxygen evolution reaction (OER) occurs. This calls for an understanding of the nature of the active OER sites and reaction intermediates, which are still being debated. In this work, we apply synchrotron radiation-based near-ambient pressure X-ray photoelectron and absorption spectroscopies under operando conditions in order to unveil the nature of the reaction intermediates and shed light on the OER mechanism on electrocatalysts most widely used in PEM electrolyzers—electrochemical and thermal iridium oxides. Analysis of the O K-edge and Ir 4f spectra backed by density functional calculations reveals a universal oxygen anion red–ox mechanism regardless of the nature (electrochemical or thermal) of the iridium oxide. The formation of molecular oxygen is considered to occur through a chemical step from the electrophilic O_I– species, which itself is formed in an electrochemical step

Insight into the Mechanisms of High Activity and Stability of Iridium Supported on Antimony Doped Tin Oxide Aerogel for Anodes of Proton Exchange Membrane Water Electrolyzers

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High energy states of gold and their importance in electrocatalytic processes at surfaces and interfaces

The ability of metals to store or trap considerable amounts of energy, and thus exist in a non-equilibrium or metastable state, is very well known in metallurgy; however, such behaviour, which is intimately connected with the defect character of metals, has been largely ignored in noble metal surface electrochemistry. Techniques for generating unusually high energy surface states for gold, and the unusual voltammetric responses of such states, are outlined. The surprisingly high (and complex) electrocatalytic activity of gold in aqueous media is attributed to the presence of a range of such non-equilibrium states as the vital entities at active sites on conventional gold surfaces. The possible relevance of these ideas to account for the remarkable catalytic activity of oxide-supported gold microparticles is briefly outlined