In this report, we present our work on development of fuel cell stacks based on proton-conducting ceramic materials. Such protonic-ceramics have demonstrated great promise for addressing the technological challenges now facing the solid-oxide fuel cell community.  Protonic ceramic fuel cells (PCFCs) based on BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3-δ have demonstrated high power density at low operating temperatures, achieving 450 mW / cm² at 500 ºC under hydrogen fuel [1, 2]. PCFCs may also be more amenable to internal reforming of hydrocarbon fuels (CH₄ + H₂O => 3 H₂ + CO). Proton conduction removes H₂from the anode stream, thereby shifting the internal-reforming equilibrium chemistry towards the products, promoting higher methane conversion.  While these materials show great promise, no multi-cell PCFC stacks have been fabricated to date.

In this presentation, we review our progress in extending previous single “button-cell” experiments to small fuel-cell stacks. The stack design is shown in Figure 1; PCFC membrane-electrode assemblies (MEAs) are bonded within a ceramic frame, and the frame is packaged within ferritic-steel interconnects. Fabrication of MEAs involves solid-state reactive sintering (SSRS), where the protonic-ceramic fuel cell material is formed from simple parent oxides during co-sintering of the anode-electrolyte assembly.  This single-step fabrication greatly reduces MEA-manufacturing costs and improves yields.

Multi-cell stack prototypes have been demonstrated. A three-cell stack based on BaCe_0.2Zr_0.6Y_0.2O_3-δ electrolyte shows open-circuit voltage that approaches the theoretical Nernst potential (Figure 1), and demonstrates excellent stability over 500 hours of continuous operation. The stack also yields reasonable power density, reaching 250 mW/cm²at 650 ºC. Moving forward, higher performance is expected as we improve fabrication and packaging methods.

Citations:

[1] C. Duan, J. Tong, M. Shang, S. Nikodemski, M. Sanders, S. Ricote, A. Almansoori, R.P, O’Hayre, “Readily processed protonic ceramic fuel cells with high performance at low temperatures,” Science 349: 6254 (2015) 1321-1326.

[2] J. Kim, S. Sengodan, G. Kwon, D. Ding, J. Shin, M. Liu, G. Kim, “Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells,” ChemSusChem 7(2014) 2811–2815.