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A recent assessment (Giovannelli, G., D'Urzo, L., Maggiulli, G., Natali, S., Pagliara, C., Sgura, I. & Bozzini, B. 2010. Journal of Solid State Electrochemistry, 14: 479–94.) of the corrosion state...

This paper reports on the electrodeposition of Mn–Cu–ZnO for hybrid supercapacitors. This material exhibits a dual structure consisting of Mn-rich highly active, but poorly electronically conducting, grains, which are locked by a Cu-rich highly conductive network that also possesses some degree of charge-storage capacity. This work focuses on morphological, compositional, and chemical-state distributions with submicrometer lateral resolution. This information, which is crucial because doping distribution controls supercapacitor performance, has been obtained by combining electrochemical and in situ Raman measurements with synchrotron-based X-ray fluorescence and absorption microspectroscopy. Using a microfabricated thin-layer three-electrode microcell, we followed the morphochemical changes at different electrodeposition stages and found that pulse-plating allows the growth of Mn- and Cu-doped ZnO as self-organized structures with a consistent spatially stable composition distribution.

This paper reports the first in-situ synchrotron-based scanning photoelectron microscopy study of an operating YSZ-supported single-chamber SOFC with Au–MnO2 composite cathode and NiO anode, fed with 10−5 mbar 1:1 mixture of CH4 fuel and O2 at 650 °C. We employed a YSZ-supported cell with Au–MnO2 composite cathode and NiO anode. The chemical imaging and micro-XPS results were complemented with simultaneous electrochemical measurements, open circuit potential, potentiostatic and impedance spectrometry. The cell was operated under two conditions: (i) with fully oxidized electrodes and (ii) after in-situ reductive activation of the anode. The current delivered by the cell after in-situ reduction was about one order of magnitude higher. The chemical states of Ni and Mn were affected by the in-situ reduction process but they were not modified by the fuel-cell operation. Notwithstanding the absence of chemical state transformations of the electrode materials during the prolonged fuel-cell operation, cell aging brings about morphological change, accompanied by a decrease of the extracted current. Keywords: SOFC, Single-chamber SOFC, Hydrocarbon-fuelled SOFC, SPEM, XPS, X-ray microscopy

The existence and role of platinum oxide in the solid state electrode system Pt(O2)/yttria-stabilized zirconia is discussed. Covering and porous model-type Pt film electrodes on YSZ single crystals are investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ scanning photoelectron microscopy. The formation of Pt oxide and its amount strongly depend on the experimental conditions, such as temperature, oxygen partial pressure, and oxygen flux towards the electrode during anodic polarization. Electrode activation and deactivation processes can be explained by formation and decomposition of Pt oxide, which is reducing or inhibiting the oxygen exchange rate.

This paper reports on the electrochemical reduction of bichromate from an aqueous solution at a Pt(1 1 1) electrode studied by voltammetry and synchrotron-based photoelectron spectromicroscopy Cathodic reduction is carried out at potentials −1.5 and −2.0 eV in an electrochemical cell attached to the UHV chamber hosting the scanning photoelectron microscope (SPEM), which allowed sample transfer for SPEM analysis without exposure to the air. The Cr 2p and Pt 4f core level spectra are used as fingerprints of the Cr lateral distribution and chemical state after reduction. The Pt 4f and Cr 2p maps show inhomogeneous Cr distribution in microscopic Cr-rich and Cr-poor islands. Analysis of the Pt 4f, Cr 2p photoemission peaks recorded in these islands has disclosed that – under both reduction conditions – Cr(VI) is reduced principally to Cr(III), with ca. 10% of Cr(0) localised in the Cr-rich islands. The presence of an intermediate oxidation state has also been detected, that can be assigned to a transition state from Cr(VI) to Cr(III).

In this paper we report an investigation of the degradation of the Pt/C electrocatalyst of an anodic membrane-electrode assembly (MEA) after 1000 h of operation in a laboratory single-cell PEMFC, using synchrotron-based space-resolved photoelectron spectroscopy. This study is complemented by the analysis of a pristine MEA and reference materials, as well as by electrochemical measurements, SEM imaging and energy-dispersive X-ray fluorescence spectroscopy (EDX). Catalyst ageing correlates with a corrugation of morphology, as observed by SEM and scanning photoelectron microscopy (SPEM), corresponding to Pt nanoparticle agglomeration. Moreover – on the basis of high lateral resolution SPEM, X-ray photoelectron spectroscopy (XPS) and EDX analyses, – we found that, after operation, Pt is transported onto the fibres of the gas-diffusion layer (GDL). Space-resolved XPS shows a peak shift of the Pt 4f 7/2 level to higher and lower binding energies with respect to Pt(1 1 1) and pristine Pt black, respectively, corresponding to nanocrystallinity in the first case and agglomeration in the second one. No oxidised Pt was found in any location of the anodically used MEA.

Cobalt/polypyrrole ORR electrocatalysts has been electrochemically synthesized by a potentiostatic anodic/cathodic pulse-plating procedure. The deposition electrochemistry has been studied by cyclic voltammetry and in-situ Micro Raman Spectroscopy complemented with scanning X-ray microscopy and micro-spot X-ray absorption spectroscopy (mu-XAS). Linear sweep voltammetry (LSV) under oxygen reduction has been used to assess the electrocatalytic effect of as-electrodeposited Co/PPy. The obtained results have provided new information about the concomitant electropolymerisation and metal incorporation processes occurring under different pulsed co-electrodeposition conditions, important for optimising the electrosynthesis procedure. The colocation of O and Co, evidenced by the O and Co XRF maps indicates that the Co in the formed composite is in oxidized state and for composites formed at low currents using shorter Co pulses coexistence of both CoO and Co3O4 is evidenced by the Co L-3 XAS spectra. Bimodal Co distribution as micro-grains on a background of nano-grains and co-nulcleation of PPy and Co is evidenced by correlation of Co and N XRF maps.

Replacement of hydrogen with hydrocarbon fuels in solid-oxide fuel cells (SOFCs) is an appealing alternative for reducing the implementation costs of SOFCs technology, but the electrode stability and susceptibility to carbon deposition still remain important issues to be solved. The present in situ photoelectron microscopy study of a prototype hydrocarbon-fuelled SOFC, operated at 650 °C in C2H4 + H2O gas mixture and voltages in the range 0−3 V, provides insights into morphologychemistry changes of the Ni electrodes and Cr interconnects with decisive impact on the electrochemical activity and durability. The results reveal the combination of thermal and electromigration of Ni across the electrode−electrolyte interface that can cause sensible material losses and structural changes responsible for the deterioration of device performance. The C 1s spectra evidence deposition of C and formation of carbides on the Ni electrodes and Cr interconnects at 650 °C as result of C2H4 dissociation, the process being promoted applying cathodic potential and reversed by switching to anodic potential. Following the attenuation of the C signal under anodic potential, the effect of the stability of different carbides on the reaction rate was observed.

The present in situ study of electrochemically induced processes occurring in Cr/Ni bilayers in contact with a YSZ electrolyte aims at a molecular-level understanding of the fundamental aspects related to the durability of metallic interconnects in solid oxide fuel cells (SOFCs). The results demonstrate the potential of scanning photoelectron microspectroscopy and imaging to follow in situ the evolution of the chemical states and lateral distributions of the constituent elements (Ni, Cr, Zr, and Y) as a function of applied cathodic potential in a cell working at 650 degrees C in 10(-6) mbar O(2) ambient conditions. The most interesting findings are the temperature-induced and potential-dependent diffusion of Ni and Cr, and the oxidation-reduction processes resulting in specific morphology-composition changes in the Ni, Cr, and YSZ areas.