Novel Perovskite Materials for Thermal Water Splitting at Moderate Temperature

Materials with the formula Sr 2 CoNb 1− x Ti x O 6− δ ( x =1.00, 0.70; δ =number of oxygen vacancies) present a cubic perovskite‐like structure. They are easily and reversibly reduced in N 2 or Ar and re‐oxidized in air upon heating. Oxidation by water (wet N 2 ), involving splitting of water at a temperature as low as 700 °C, produces hydrogen. Both compounds displayed outstanding H 2 production in the first thermochemical cycle, the Sr 2 CoNb 0.30 Ti 0.70 O 6− δ material retaining its outstanding performance upon cycling, whereas the hydrogen yield of the x =1 oxide showed a continuous decay. The retention of the materials’ ability to promote water splitting correlated with their structural, chemical, and redox reversibility upon cycling. On reduction/oxidation, Co ions reversibly changed their oxidation state to compensate the release/recovery of oxygen in both compounds. However, in Sr 2 CoTiO 6− δ , two phases with different oxygen contents segregated, whereas in Sr 2 CoNb 0.30 Ti 0.70 O 6− δ this effect was not evident. Therefore, this latter material displayed a hydrogen production as high as 410 μmolH2 g −1 perovskite after eight thermochemical cycles at 700 °C, which is among the highest ever reported, making this perovskite a promising candidate for thermosolar water splitting in real devices.