Lowering the operating temperature of protonic ceramic electrochemical cells to <450 °C

Protonic ceramic electrochemical cells (PCECs) can be employed for power generation and sustainable hydrogen production. Lowering the PCEC operating temperature can facilitate its scale-up and commercialization. However, achieving high energy efficiency and long-term durability at low operating temperatures is a long-standing challenge. Here, we report a simple and scalable approach for fabricating ultrathin, chemically homogeneous, and robust proton-conducting electrolytes and demonstrate an in situ formed composite positive electrode, Ba0.62Sr0.38CoO3−δ–Pr1.44Ba0.11Sr0.45Co1.32Fe0.68O6−δ, which significantly reduces ohmic resistance, positive electrode–electrolyte contact resistance and electrode polarization resistance. The PCECs attain high power densities in fuel-cell mode (~0.75 W cm−2 at 450 °C and ~0.10 W cm−2 at 275 °C) and exceptional current densities in steam electrolysis mode (−1.28 A cm−2 at 1.4 V and 450 °C). At 600 °C, the PCECs achieve a power density of ~2 W cm−2. Additionally, we demonstrate the direct utilization of methane and ammonia for power generation at <450 °C. Our PCECs are also stable for power generation and hydrogen production at 400 °C. The typically high temperatures (≥500 °C) at which ceramic electrochemical cells operate place constraints on device materials and construction. Here Liu and colleagues design reversible proton-conducting electrochemical cells that can operate with high performance at temperatures of 450 °C and below.