Processing Ceramic Proton Conductor Membranes for Use in Steam Electrolysis

Steam electrolysis constitutes a prospective technology for industrial-scale hydrogen production. The use of ceramic proton-conducting electrolytes is a beneficial option for lowering the operating temperature. However, a significant challenge with this type of electrolyte has been upscaling robust planar type devices. The fabrication of such multi-layered devices, usually via a tape casting process, requires careful control of individual layers' shrinkages to prevent warping and cracks during sintering. The present work highlights the successful processing of 50 × 50 mm² planar electrode-supported barium cerium yttrium zirconate BaZr_0.44Ce_0.36Y_0.2O_2.9 (BZCY(54)_8/92) half cells via a sequential tape casting approach. The sintering parameters of the half-cells were analyzed and adjusted to obtain defect-free half-cells with diminished warping. Suitably dense and gas-tight electrolyte layers are obtained after co-sintering at 1350 °C for 5 h. We then assembled an electrolysis cell using Ba_0.5La_0.5CoO_3-δ as the steam electrode, screen printed on the electrolyte layer, and fired at 800 °C. A typical Ba_0.5La_0.5CoO_3-δ|BaZr_0.44Ce_0.36Y_0.2O_3-δ(15 μm)|NiO-SrZr_0.5Ce_0.4Y_0.1O_3-δ cell at 600 °C with 80% steam in the anode compartment reached reproducible terminal voltages of 1.4 V @ 500 mA·cm^-2, achieving ~84% Faradaic efficiency. Besides electrochemical characterization, the morphology and microstructure of the layered half-cells were analyzed by a combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy. Our results also provide a feasible approach for realizing the low-cost fabrication of large-sized protonic ceramic conducting electrolysis cells (PCECs).