Abstract
The intermediate operating temperatures (~400–600 °C) of reversible protonic ceramic fuel cells (RePCFC) permit the potential use of ammonia as a carbon-neutral high energy density fuel and energy storage medium. Here we show fabrication of anode-supported RePCFC with an ultra-dense (~100%) and thin (4 μm) protonic ceramic electrolyte layer. When coupled to a novel Ru-(BaO)2(CaO)(Al2O3) (Ru-B2CA) reversible ammonia catalyst, maximum fuel-cell power generation reaches 877 mW cm−2 at 650 °C under ammonia fuel. We report relatively stable operation at 600 °C for up to 1250 h under ammonia fuel. In fuel production mode, ammonia rates exceed 1.2 × 10−8 NH3 mol cm−2 s−1at ambient pressure with H2 from electrolysis only, and 2.1 × 10−6 mol NH3 cm−2 s−1 at 12.5 bar with H2 from both electrolysis and simulated recycling gas.
Highlights
The intermediate operating temperatures (~400–600 °C) of reversible protonic ceramic fuel cells (RePCFC) permit the potential use of ammonia as a carbon-neutral high energy density fuel and energy storage medium
While prior ammonia-based applications of protonic ceramic cells have largely pursued a fully-integrated, single reactor approach, here we deliberately pursue a decoupled design, where separate reactors are used for power generation/electrochemical water splitting and ammonia cracking/thermochemical ammonia synthesis
While previous high flow-rate, high pressure packed-bed reactor experiments identify a clear peak in Ru-B2CA NH3 synthesis performance at ~490 °C35, the ambient pressure, low flow-rate reactor we developed to integrate with the RePCFC in the present work leads to a broader, lower-temperature peak in performance from ~350–450 °C (Fig. 1e)
Summary
The intermediate operating temperatures (~400–600 °C) of reversible protonic ceramic fuel cells (RePCFC) permit the potential use of ammonia as a carbon-neutral high energy density fuel and energy storage medium. NH3 has a much narrower explosive limit in air (15–28 vol %) in contrast to compressed hydrogen (4–75 vol %) and methanol (~7–36 vol %), and a high auto-ignition temperature (650 °C) that reduces flammability risk during storage and transportation[24]. With these advantages in mind, an energy system that can combine the advantages of both RePCFCs and NH3 fuel may be very attractive for space-tight and high energydensity applications such as in fuel cell vehicles, unmanned aerial vehicles, and seasonal-term large scale energy storage
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