Development of tubular proton ceramic electrolysis cells for pressurized operation
Incentives for developing high temperature electrolysers (HTEs) using proton conducting electrolytes stem from the fact that a proton ceramic electrolysis cell (PCE) pumps out and pressurizes dry H2 directly. Existing HTEs design utilizes the high packing density of planar stacks, but the hot seal and vulnerability to single cell breakdown give high stack rejection rate and questionable durability and lifetime economy. We develop instead tubular cells enabling to reduce the sealing areas, that are more robust to pressurized and transient operation. The cells consist of a porous Ni-BaZr1-x-yCexYyO3-d (BZCY) cathode for the H2 side, a dense thin BZCY-based electrolyte, and a porous nanostructured composite anode for the H2O side. This electrode is made of BZCY combined with the double perovskite Ba1-xGd0.8La0.2+xCo2O6-δ (BGLC). The tubular cells are developed using scalable manufacturing routes based on plastic extrusion, spray-coating and dip-coating using environmentally friendly chemicals. A key feature of the manufacturing process lies in the use of solid-state reactive co-sintering of the electrolyte with the NiO-BZCY electrode. This is achieved by preparing the tubular composite electrodes with plastic extrusion of a precursor mixture of the desired oxides, using BaSO4, CeO2, Y2O3, ZrO2 and NiO powders. After drying, the green tubes are coated with an electrolyte suspension, also made of the precursor mixture of the targeted electrolyte composition. Co-firing of these assemblies yields the formation of the desired materials and microstructures. The air electrode is then dip-coated and annealed in air. Extensive characterization using thermal analysis (TGA, DTA), environmental SEM, optical dilatometry and push-rod dilatometry in various atmospheres, and HT-XRD has been carried out to determine the sintering mechanisms and improve the thermal treatment of these assemblies. The cells were successfully upscaled from 12 cm2 up to 60 cm2 active surface area. Electrochemical characterisation of the produced cells confirms the impact of the processing parameters on the cell's performance. Results of this work will be presented in the present contribution.