Micro-structured thin-film electrodes were employed to investigate the capacitive behavior of nickel on yttria-stabilized zirconia (YSZ) electrolytes by means of electrochemical impedance spectroscopy. Electrodes with different shapes and electrode areas clearly showed a linear relationship between capacitance and the electrode area. Electrostatic double layer models, however, could not explain the observed area specific capacitance value of ca. 3 F/m(2). This fact, the characteristic voltage dependence with a hysteresis, and the effect of H2S on the electrode capacitance indicate substantial contributions of a chemical capacitance. Possible types of chemical capacitance in the system Ni(H-2/H2O)/YSZ are discussed and an oxygen partial pressure dependent mechanism change is suggested. (C) The Author(s) 2016. Published by ECS. All rights reserved.