title: Correlation between hydrogen production rate, current, and electrode overpotential in a solid oxide electrolysis cell with La0.6Sr0.4FeO3-δthin-film cathode.
abstract: A solid oxide electrolysis cell (SOEC) with a model-type La0.6Sr0.4FeO3-δthin-film cathode (working electrode) on an yttria-stabilized zirconia electrolyte and a porous La0.6Sr0.4Co0.2Fe0.8O3-δcounterelectrode was operated in wet argon gas at the cathode. The hydrogen formation rate in the cathode compartment was quantified by mass spectrometry. Determination of the current as well as outlet gas composition revealed the electrochemical reduction of some residual oxygen in the cathodic compartment. Quantitative correlation between gas composition changes and current flow was possible. At 640 °C a water-to-hydrogen conversion rate of ca. 4 % was found at -1.5 V versus a reversible counterelectrode in 1 % oxygen. Onset of hydrogen formation could already be detected at voltages as low as -0.3 V. This reflects a fundamental difference between steam electrolysis and electrolysis of liquid water: substantial hydrogen production in a SOEC is already possible at pressures much below ambient. This causes difficulties in determining the cathodic overpotential of such a cell.
authors.affiliation: Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
authors.forename: Gregor
authors.initials: G
authors.lastname: Walch
authors.affiliation: Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
authors.forename: Alexander Karl
authors.initials: AK
authors.lastname: Opitz
authors.affiliation: Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
authors.forename: Sandra
authors.initials: S
authors.lastname: Kogler
authors.affiliation: Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Fleig
keywords: Cathode; Electrochemistry; Electron transfer; Overpotential; Oxides