Local current measurement in a solid oxide fuel cell repeat element

A planar solid oxide fuel cell repeating unit, 50 cm(2) in total active electrode size, consisting of an anode supported electrolyte cell bearing two 7 turn holes for fuel and air injection, and contacted to two dense metal current collector plates via gas distribution layers, was constructed with the aim of measuring local current densities rather than the integral current over the full area. The cathode side was entirely segmented (i.e. cathode layer, gas distribution layer, metal current collector plate) into eight galvanically separated parts of ca. 6.5 cm(2) each, with own current and potential leads. The element was characterised at 750-800 degrees C and different H-2 fuel flows, by total and local current-voltage recording as well as by local electrochemical impedance measurement. The segment that incorporates the fuel injection hole for the whole cell always outperforms all other segments, the corner segments furthest away from the fuel injection perform least. Differences in local potential can be higher than 200 mV. Polarizing one segment individually and recording the change in potential of the other segments reveals the different contributions of convection and diffusion on the flow field. Contrarily to small ideal single cells, total performance of such larger sized, stackable cells is decisively governed by the distribution fields and their weakest zones. (c) 2006 Elsevier Ltd. All rights reserved.