Highly efficient reversible protonic ceramic electrochemical cells for power generation and fuel production

Reversible fuel cells based on both proton exchange membrane fuel cell and solid oxide fuel cell technologies have been proposed to address energy storage and conversion challenges and to provide versatile pathways for renewable fuels production. Both technologies suffer challenges associated with cost, durability, low round-trip efficiency and the need to separate H2O from the product fuel. Here, we present a reversible protonic ceramic electrochemical cell based on an yttrium and ytterbium co-doped barium cerate–zirconate electrolyte and a triple-conducting oxide air/steam (reversible) electrode that addresses many of these issues. Our reversible protonic ceramic electrochemical cell achieves a high Faradaic efficiency (90–98%) and can operate endothermically with a >97% overall electric-to-hydrogen energy conversion efficiency (based on the lower heating value of H2) at a current density of −1,000 mA cm−2. Even higher efficiencies are obtained for H2O electrolysis with co-fed CO2 to produce CO and CH4. We demonstrate a repeatable round-trip (electricity-to-hydrogen-to-electricity) efficiency of >75% and stable operation, with a degradation rate of <30 mV over 1,000 h. Reversible electrochemical cells can operate in both fuel cell and electrolysis modes to interconvert between chemical and electrical energy. Here, Duan et al. design a reversible protonic ceramic electrochemical cell that operates stably at 500–600 °C, with high Faradaic and round-trip efficiencies, by minimizing electronic leakage.