Many of the fundamental processes that underlie the function fuel cells occur at or near interfaces. To date, idealized experiments, ex-situ analysis, operando spectroscopy, and macroscopic electrical property measurements, have driven advancements in SOFCs, however, in-situ (operando) imaging techniques capable of locally resolving the governing electrochemical phenomena under realistic operating conditions have remained largely elusive.
The scanning probe approach presented here demonstrates, for the first time, direct imaging of local interfacial potential perturbations across electrode-electrolyte interfaces (Fig. a). By comparing fuel cells based on two common electrode materials; lanthanum-strontium-ferrite (LSF) and lanthanum-strontium-manganite (LSM), we also demonstrate the ability to image and distinguish between bulk-mediated and surface mediated transport mechanisms, identify both the active zone and triple phase boundary regions, and directly estimate activation barrier changes in these systems.
The development of miniature sample chambers enables high temperature scanning of SOFCs in cross sectional geometries. The images shown here are of LSF-YSZ-LSF symmetrical fuel cells, under operation, at 600°C. Topographic (Fig. d) and scanning surface potential are shown for the cathode (Fig. g), electrolyte (Fig. c), and anode (Fig. e) cell constituents, respectively. Line profile analysis averaged between the dotted red lines display a distinct, localized perturbation occurring along the electrolyte/electrode interface (Figs. b,i). This result demonstrates the influence of trapped ionic oxygen at the interface, which perturbs the local chemical potential and subsequently the surface potential. This phenomenon is supported by the presence of an Ohmic-like response within the yttria-stabilized-zirconia (YSZ) electrolyte, which conducts only ions, not electrons. These results also pose significant implications for direct identification of active zones within the electrodes, as evident by the distance over which the perturbations occur.