Scale up of Proton-Conducting Ceramics into Multi-Cell Stacks

Abstract

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 no demonstrations of multi-cell stacks. Through support from the U.S. Department of Energy, researchers at the Colorado School of Mines are scaling up protonic-ceramic devices from the button-cell level into small, multi-cell stacks as illustrated in the figure. Both fuel-cell and electrolyzer stacks are in development. The order-of-magnitude increases in the physical size of the delicate membrane-electrode assembly (MEA) bring concerns regarding mechanical strength and robustness. The compatibility of protonic-ceramic materials with stack-packaging materials – metallic interconnects, current collectors, glass-ceramic sealants, and gaskets – has witnessed limited study. In this presentation, we describe selection and tuning of materials, fabrication procedures, and operating conditions to achieve reasonable performance and low degradation in protonic-ceramic fuel cells (PCFCs) stacks.We find highest stack electrochemical performance and durability when utilizing electrolytes based on BaCe0.4Zr0.4Y0.1Yb0.1O3-d (BCZYYb). The anode support is a nickel-electrolyte composite, while the cathode is BaCe0.4Fe0.4Zr0.1Y0.1O3-d (BCFZY). The planar MEAs reach 5 cm2 in active area. The circular stack design enables a measure of flexibility in MEA physical size and shape, and provides balance in stress distribution from thermal- and chemical-expansion. The MEAs are packaged within ferritic-steel interconnects and macor frames to form multi-cell stacks. Our three-cell stack demonstrates encouraging performance, reaching 0.69 and 0.47 W cm-2 under H2 and CH4 fuels, respectively, at 600 ºC. A cathode-electrolyte interlayer of 10%-gadolinium-doped ceria proves critical in achieving stack degradation as low as 1.5% kh-1. Figure 1