Electrically Enabled Isothermal CeO2 Thermochemical Water Splitting below 900 °C

Ceria-based thermochemical cycles offer a promising route to solar hydrogen, but require reduction above 1400 °C and large temperature swings. Here, building on electrically assisted CeO2 reduction, we demonstrate repeated isothermal CeO2-based water-splitting cycles at 700–900 °C and 0.5–2.0 V. Porous CeO2−YSZ bilayer pellets with different composition ratios undergo electrically assisted reduction and steam re-oxidation at the same temperature, producing O2 and H2 in separate steps without thermal cycling. The process reaches H2/O2 ratios up to 1.9, reproducible H2 productivity over 10 cycles, and H2 yields up to 49 ± 2 μmol gCeO2−1 cycle−1 after only 20 min of electrically assisted reduction. Extended-reduction experiments show that the best composition remains only ∼0.10 V below the applied bias on an equivalent thermodynamic-voltage basis. Reactor-scale projections based on gas utilization in an existing ceria reactor give a solar-to-H2 efficiency of 5.6% without assuming improvements to the CeO2−YSZ architecture.