Proton-conducting ceramics are emerging as an enabling material for efficient electricity generation, energy storage, and fuels synthesis. While recent advancements at the lab-scale are highly encouraging, there are few reports of scaling cell size beyond the button cell, and limited demonstrations of multi-cell stacks. The first part of this work is focusing on scaling up protonic-ceramic devices. The order-of-magnitude increases in the physical size of the delicate membrane-electrode-assembly (MEA) bring concerns regarding mechanical-strength and robustness. Consequently, the compatibility of protonic-ceramic materials with stack-packaging materials is subject to investigation in this study. The initial degradation rates of protonic-ceramics stacks was found to be intense, especially at lower temperatures under fuel-cell operation mode. Operating conditions are shown to have a large impact on degradation rates in our protonic-ceramics. Lower degradation rates are observed under electrolysis operation, and at higher operating temperatures. Electrochemical Impedance Spectroscopy reveals the nature of the electrochemical processes is closely tied to the degradation behaviors observed in our experiments. The impact of a gadolinium-doped ceria (GDC) interlayer on improving the durability of the cells is reported, especially at low temperatures. This is perhaps a surprise, as GDC is a common O2−-conducting material, and perhaps ill-matched to protonic ceramics. Regardless, the presence of the GDC layer at the air electrode-electrolyte interface has proven to be an effective strategy for minimizing protonic-ceramics degradation throughout the research, falling to 1.2% / 1,000 hrs for the methane-fueled stack at 600◦C. Finally, efforts to utilize proton-conducting electrolyzer at elevated pressures and temperatures are presented. The high operating pressure enables electrochemical ammonia synthesis from H2O and N2 feedstocks. In this concept, renewable electricity is used to drive hydrogen production through high-temperature water splitting in the protonic-ceramic electrolyzer. The hydrogen mixes with nitrogen and is then converted to NH3 over a ruthenium catalyst. The process is executed at pressures up to 12.6 bar at 550◦C, bringing significant challenges in packaging of the protonic ceramic and the catalyst. In this work, the progress in establishing pressurized operation and the benefits it brings to electrochemical performance and ammonia production will be reviewed.
Copyright of the original work is retained by the author.
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