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Abstract The proton‐conducting solid oxide electrolysis cell (H‐SOEC) is a promising device that converts electrical energy to chemical energy. H‐SOECs have been actively studied in the past few years, due to their advantages over oxygen‐ion‐conducting solid oxide electrolysis cells (O‐SOECs), such as lower operation temperature, relatively lower activation energy, and easier gas separation. A critical overview of recent progress in H‐SOECs is presented, focusing particularly on the period from 2014 to 2018. This review focuses on three aspects of H‐SOECs, namely, the materials, modeling, and current leakage in proton conducting oxide electrolytes. Specifically, the current leakage in proton conducting oxides, which is often neglected, leads to two problems in the studies of H‐SOECs. One is the distortion of the electrochemical impedance spectra and the other is low faradaic efficiency of electrolysis. Based on the comprehensive and critical discussion in these three sections, challenges in the development of H‐SOECs are highlighted and prospective research in H‐SOECs is outlined.
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Theoretical understanding of stability of the oxygen electrode in a proton-conductor based solid oxide electrolysis cell
The oxygen electrode in a proton-conductor based solid oxide cells is often a triple-conducting material that enables the transport and exchange of electrons (e-), oxygen ions (O2-), and protons (H+), thus expanding active areas to enhance the oxygen electrode activity. In this work, a theoretical model was developed to understand stability of tri-conducting oxygen electrode by studying chemical potentials of neutral species (i.e., μ_(O_2)^ , μ_(H_2)^ , and μ_(H_2 O)^ ) as functions of transport properties, operating parameters, and cell geometry. Our theoretical understanding shows that: (1) In a conventional oxygen-ion based solid oxide cell, a high μ_(O_2)^ (thus high oxygen partial pressure) exists in the oxygen electrode during the electrolysis mode, which may lead to the formation of cracks at the electrode/electrolyte interface. While in a proton-conductor based solid oxide cell, the μ_(O_2)^ is reduced significantly, suppressing the crack formation, and resulting in improved performance stability. (2) In a typical proton-conductor based solid oxide electrolyzer, the dependence of μ_(O_2)^ on the Faradaic efficiency is negligible. Hence, approaches to block the electronic current can improve the electrolysis efficiency while achieving stability. (3) The difference of the μ_(O_2)^ (thus p_(O_2)^ ) between the oxygen electrode and gas phase can be reduced by using higher ionic conducting components and improving electrode kinetics, which lead to further improvement of electrode stability.
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- Award ID(s):
- 1920166
- PAR ID:
- 10409687
- Date Published:
- Journal Name:
- International journal of hydrogen energy
- ISSN:
- 0360-3199
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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