Faradaic efficiency in protonic-ceramic electrolysis cells
Huayang Zhu, Sandrine Ricote, Robert J. Kee
Abstract
Abstract Proton-conducting ceramics (e.g. doped barium zirconates or cerates) are typically mixed ionic-electronic conductors (MIECs). The electronic conduction, typically in the form of positively charged small polarons or electron holes, leads to ‘electronic leakage.’ In an ideal steam-electrolysis cell, one gas-phase H 2 molecule is produced from every two electrons delivered from an external power source. In other words, such ideal behavior achieves 100% faradaic efficiency. However, the electronic flux associated with MIEC membranes contributes to reduced faradaic efficiency. The present paper develops a model that predicts the behavior of faradaic efficiency as a function of electrolysis-cell operating conditions. Although the model framework is more general, the paper focuses on the behavior of a cell based upon a BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>−</mml:mo> <mml:mi>δ</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> (BCZYYb) membrane. The study predicts the effects of operating conditions, including temperature, pressure, and gas compositions.