Novel perovskite materials for thermal water splitting at moderate temperature.

Materials with the formula Sr2CoNb1-xTixO6-delta (x=1.00, 0.70; delta=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 degrees C, produces hydrogen. Both compounds displayed outstanding H-2 production in the first thermochemical cycle, the Sr2CoNb0.30Ti0.70O6-delta 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 Sr2CoTiO6-delta, two phases with different oxygen contents segregated, whereas in Sr2CoNb0.30Ti0.70O6-delta this effect was not evident. Therefore, this latter material displayed a hydrogen production as high as 410 mu molH2 g(perovskite)(-1) after eight thermochemical cycles at 700 degrees C, which is among the highest ever reported, making this perovskite a promising candidate for thermosolar water splitting in real devices.