Steam Electrolysis by Proton-Conducting Solid Oxide Electrolysis Cells (SOECs) with Chemically Stable BaZrO3-Based Electrolytes
The few works reporting on proton-conducting SOECs show the use of BaCeO3-based electrolytes, which has been demonstrated to be chemically unstable in H2O. Although proton-conducting BaZrO3-based materials are the most promising electrolyte candidates for proton-conducting SOECs due to the excellent chemical stability and high bulk conductivity , their processing difficulties due to poor sinterability and high-resistive grain boundaries prevented the deployment in SOEC devices. In this report, we pioneeringly used BaZrO3-based electrolytes for SOECs, demonstrating that tailoring the electrolyte and electrode materials results in further improving the electrolysis cell performance.
Anode supported BaZr0.9Y0.1O3-δ (BZY) electrolyte films were fabricated using an ionic diffusion method . Both thermodynamic calculation and experimental results suggest that BZY has an excellent chemical stability in H2O, which is critical for practical applications. A current density of 119 mA cm-2 was obtained at 600°C, with an applied voltage of 1.65 V for the electrolysis cell, which is comparable or even higher than that for proton-conducting SOECs with BaCeO3-based electrolyte at similar conditions, while BZY electrolyte offers much better chemical stability. This cell also operated at 600 oC for more than 80 h without any obvious degradation, while the BaCeO3-cells are reported to only last tenths of minutes or a few hours .
To improve the cell performance, BaZr0.7Y0.2Pr0.1O3-δ (BZPY10), which is a more conductive proton-conducting electrolyte material, wass used for the SOEC. With La0.8Sr0.2MnO3-δ (LSM)-BZPY10 composite air electrode, the SOEC with BZPY10 electrolyte reached a current density of 576 mA cm-2 with an applied voltage of 1.6 V at 600 oC. This cell performance is much improved compared with the above discussed BZY cell. Further cell performance improvement was achieved by tailoring the air electrode material with BaZr0.5Y0.2Pr0.3O3-δ (BZPY30), which is a mixed protonic-electronic conductor rather than a pure protonic conductor . By coupling BZPY30 with LSM, the triple phase boundary (TPB) is much improved due to the mixed conducting behavior of BZPY30, which is beneficial to the reaction. As a result, the cell with BZPY30-LSM air electrode produced a current density of 1007 mA cm-2 with an applied voltage of 1.6 V at 600 oC. An obvious cell performance improvement is obtained with the tailored electrode.
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