La0.6Sr0.4Co0.2Fe0.8O3 - delta (LSCF), La2NiO4 + delta (LNO), La0.87Sr0.13CrO4 (LSC), La0.8Sr0.2MnO3 - delta (LSM) and Ba0.5Sr0.5Co0.8Fe0.2O3 - delta (BSCF) composite anodes deposited on proton-conducting BaCe0.2Zr0.7-Y0.1O3 - delta (BCZY27) electrolytes were studied as steam electrolysis anodes in symmetric cells. The effect of the electrode composition and microstructure on the electrochemical behavior was investigated using impedance spectroscopy in the 800-500 degrees C range under 3 bar of pressure of wet air (75% of steam). The first screening revealed that 50-50 (vol%) LSCF/BCZY27 composite anodes show the best performance, reaching polarization resistances <0.68 Omega.cm(2) at 700 degrees C and high steam pressure (0.75 bar of air and 225 bar of steam). The performance of the LSCF/BCZY27 composite was further improved by changing the ratio of the different phases. Finally the anode operation conditions (steam, oxygen and total pressures) were systematically varied in order to identify and characterize the different electrochemical processes that take place in the anode under realistic operation. (C) 2017 Elsevier B.V. All rights reserved.