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_0.44 Ce_0.36 Y_0.2 O_2.9 (BZCY(54)_8/9 2) 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_0.5 La_0.5 CoO_3−δ as the steam electrode, screen printed on the electrolyte layer, and fired at 800^◦ C. A typical Ba_0.5 La_0.5 CoO_3−δ |BaZr_0.44 Ce_0.36 Y_0.2 O_3−δ (15 µm)|NiO-SrZr_0.5 Ce_0.4 Y_0.1 O_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).