Thermally and electrochemically driven O-18 tracer exchange experiments in H-2/(H2O)-O-18 atmosphere were performed on SrTi0.7Fe0.3O3 (- delta) and Ce0.8Gd0.2O2 - delta thin films on single crystalline YSZ substrates. Noble metal current collectors were deposited on both films and electrochemically polarized during the exchange experiment The resulting tracer distribution was analyzed by spatially resolved secondary ion mass spectrometry. Increased tracer fraction near the current collectors was found under cathodic polarization and decreased tracer fraction under anodic polarization. High cathodic bias leads to enhanced n-type electronic conductivity, which increases the extent of the electrochemically active zone. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license