Novel perovskite materials for thermal water splitting at moderate temperature

Abstract

Materials with formula Sr2CoNb1-xTixO6-δ (x = 1.00, 0.70) present a cubic perovskite-like structure. They are easily and reversibly reduced (in N2 or Ar) and re-oxidized (in air) upon heating. Oxidation by water, (wet N2), involving splitting of water at a temperature as low as 700ºC, produces hydrogen. Both compounds display outstanding H2 production in the first thermochemical cycle, the Sr2CoNb0.30Ti0.70O6-δ material retaining its outstanding performance upon cycling, whereas the hydrogen yield of the x=1 oxide shows a continuous decay. The retention of the materials’ ability to promote water splitting correlates with their structural, chemical and redox reversibility upon cycling. On reduction/oxidation, Co ions reversibly change their oxidation state to compensate the release/recovering of oxygen in both compounds. However, in Sr2CoTiO6-δ two phases with different oxygen contents segregate, whereas in Sr2CoNb0.30Ti0.70O6-δ this effect is no evident. Therefore, this latter material displays a hydrogen production as high as 410 μmolH2/gperovskite after 8 thermochemical cycles at 700ºC, among the highest ever reported, making this perovskite a promising candidate for thermo-solar water splitting in real devices.