An in situ near-ambient pressure X-ray Photoelectron Spectroscopy study of Mn polarised anodically in a cell with solid oxide electrolyte

Abstract

This paper reports an in situ study of the anodic behavior of a model solid oxide electrolysis cell (SOEC) by means of near-ambient pressure X-ray Photoelectron Spectroscopy (XPS) combined with near edge X-ray absorption fine structure (NEXAFS) measurements. The focus is on the anodic surface chemistry of MnO_x, a model anodic material already considered in cognate SOFC-related studies, during electrochemical operation in CO₂, CO₂/H₂O and H₂O ambients. The XPS and NEXAFS results we obtained, complemented by electrochemical measurements and SEM characterisation, reveal the chemical evolution of Mn under electrochemical control. MnO is the stable chemical form at open-circuit potential (OCP), while Mn₃O₄ forms under anodic polarisation in all the investigated gas ambients. Carbon deposits are present on the Mn electrode at OCP, but they are readily oxidised under anodic conditions. Prolonged operation of the MnO_x anode leads to pitting of the Mn films, damaging of the triple-phase boundary region and also to formation of discontinuities in the Mn patch. This is accompanied by chemical transformations of the electrolyte and formation of ZrC without impact on the surface chemistry of the Mn-based anode

An in situ near-ambient pressure X-ray photoelectron spectroscopy study of CO 2 reduction at Cu in a SOE cell

“…Even though studies on planar solid-oxide cells exposed to just a single reactive gas are not identical to those on real SOECs in which the fuel and the oxidant are separately brought into contact with optimised, highlyactive working and counter electrodes, nevertheless mechanistic information gathered from this type of study is directly related to the relevant electrodic processes. The specific cell rationale, geometry, electrode fabrication and electrochemical characterisation have been detailed in a dedicated paper [41]. Over the years, we have developed lithographed planar cells for in situ micro-XPS in view of two main objectives: (i) to render the whole electrochemical system (cathode, electrolyte and anode) accessible to the X-ray beam; (ii) to confine the region exhibiting the highest electrochemical activity to the surface, to which of course XPS is uniquely sensitive.…”

“…[42]), in our planar lithographed cells the electrochemically active triple-phase boundaries are provided by the contact lines between electrode and electrolyte, exposed to the gas ambient of the 5 analysis chamber. The choice and behaviour of the counter-electrode is detailed in [41]. Cu has been selected as the cathode in order to be able to single out the contribution of this element to the cathodic operation of…”

“…Full details of the electrochemical measurements can be found in our previous paper [41]. Here we briefly recapitulate the essential linear sweep voltammetry (LSV) information.…”

“…At open-circuit, two peaks can be clearly separated at 530.0  0.1 and 531.5  0.1 eV, shifting to 529.6  0.1 and 530.9  0.1 eV, respectively, when applying the potential. It is worth noting that, as detailed in [41], we operated in a way that ensures that spectral shifts are not due to charging effects resulting from the application of the electrochemical polarisation. The peak at 530.9 eV is compatible with the presence of Cu 2 O [47][48][49] and its intensity correlates with that of the Cu shake-up features of Figure 3a.…”

“…reduction reaction by near-ambient pressure (NAP) XPS and NEXAFS complemented by electrochemical measurements of two-probe linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS), detailed in[41].…”