Understanding Direct-Ammonia Protonic Ceramic Fuel Cells: High-Performance in the Absence of Precious Metal Catalysts

Abstract

Ammonia has received considerable attention as a promising carbon-free hydrogen carrier. At temperatures above 400 °C, NH₃ is thermodynamically unstable with respect to decomposition into nitrogen and hydrogen and is, thus, suitable for direct use in solid oxide fuel cells (SOFCs) without external reforming. However, poor catalytic activity for ammonia decomposition at the moderate temperatures of protonic ceramic fuel cell (PCFC) operation has resulted in low fuel cell power output relative to operation on hydrogen and likely contributes to reported cell degradation. Here we prepared cells based on a thermodynamically robust electrolyte, a high activity cathode, and an anode with a distinctive structure to overcome challenges of poor activity and stability. The cells delivered peak power densities of 0.59 and 0.44 W cm^–2 under H₂ and NH₃, respectively, at 500 °C, excellent stability over a period of 200 h, and no detectable NO_x in the anode exhaust gas.