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 °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.

X-ray techniques allow one to carry out imaging with nanometric resolution in situ, during electrodeposition processes. In this paper, we describe the pioneering application of soft X-ray microscopy to Ni electrodeposition from ammonium and chloride solutions. Morphological features typical of the relevant electrochemical process in a thin-layer cell were successfully imaged and followed dynamically as a function of the applied electrochemical polarization. In particular, grainy films, dendrites, and blisters were detected and their locations were rationalized in terms of current density distribution. Furthermore, the electrochemical system implemented at the TwinMic beamline has been proved to support in situ spectroscopic work that will be described in a subsequent publication.

Following our systematic investigations on the durability of solid oxide fuel cell (SOFC) components (Bozzini, B.; Tondo, E.; Prasciolu, M.; Amati, M.; Kazemian, M.; Gregoratti, L.; Kiskinova, M. ChemSusChem, http://dx.doi. org/10.1002/cssc.201100140), the present in situ scanning photoelectron microscopy study is focused on the redox behavior of Ni−Cu bilayers in contact with Cr, representing the anodic material and interconnects for SOFCs, respectively.The experiments with this model cell, using yttria-stabilized zirconia (YSZ) electrolyte, were carried out in 2 × 10 −6 mbar O 2 at 650°C at open circuit potential (OCP) and under applied potential. The elemental images and the spectra from selected parts of the cell have revealed dramatic compositional and morphological changes under OCP conditions, yielding Ni−Cu islands covered with NiO in the electrode region and a NiO network in the YSZ electrolyte region. The Ni reduction dynamics as a function of applied potential is followed by continuous monitoring of the evolution of the Ni 2p spectra in different regions, which allowed the location of electrochemically active areas of the half-cell upon cathodic polarization. It was shown that after electrochemical reduction the reoxidation at OCP results in notable morphology alterations of the triple-phase contact region, which can be related to the empirically observed degradation of catalytic performance.

No abstract

No abstract

No abstract

No abstract

No abstract