Novel Perovskite Materials for Thermal Water Splitting at Moderate Temperature

Abstract

Materials with the formula Sr2CoNb1−xTixO6−δ (x=1.00, 0.70; δ=number of oxygen vacancies) 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 700 °C, produces hydrogen. Both compounds displayed 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 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−δ, two phases with different oxygen contents segregated, whereas in Sr2CoNb0.30Ti0.70O6−δ this effect was not evident. Therefore, this latter material displayed a hydrogen production as high as 410 μmolnormalH2 g−1perovskite 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.

A Review of Oxygen Carrier Materials and Related Thermochemical Redox Processes for Concentrating Solar Thermal Applications

“…The best conversion yield, obtained with 75% heat recovery at 1300 • C, only reached 1.36% and a very high amount of CO produced per cycle (1400-1700 µmol/g) was reported, which needs to be confirmed. Sr 2 CoNb 0.3 Ti 0.7 O 6 was reported to exhibit a production of H 2 as high as 410 µmol/g during eight consecutive cycles [143]. The most surprising fact is that the cycles were realized isothermally at 700 • C. A La 0.6 Ca 0.4 Mn 0.7 Al 0.3 O 3 material coated on reticulated ceramic foams was studied [144].…”

Light-assisted thermochemical reduction of CuFe2O4 within a photo-thermogravimetric analyser for solar fuel production

“…Zhang et al [26] presented a synthesis method of CuFe 2 O 4 and its application in a two-step water-splitting cycle. Azcondo et al [27] proposed a novel perovskite material, Sr 2 CoNb 1−x Ti x O 6−δ , for water splitting at a moderate operating temperature of 700 • C. Optimised materials could also lower the operating temperature to below 1000 • C, but their reaction reactivity and long-term cycling stability remains uncertain [28].…”

Sodium Manganese Ferrite Water Splitting Cycle: Unravelling the Effect of Solid–Liquid Interfaces in Molten Alkali Carbonates

“…8,11,12 The main advantages of WSTCs over the direct thermal water decomposition are (a) the reduction of the operating temperature to 500−1800 °C and (b) not requiring downstream hydrogen and oxygen separation since they are released in different reaction steps. 11,13 Mixed ferrites (MFe 2 O 4 ) are promising materials for water splitting. In these oxides the Fe 2+ of the ferrite is partially substituted by other bivalent cations such as Ni, Co, Zn, and Mn.…”

“…A water-splitting thermochemical cycle (WSTC) is a cyclic succession of chemical reactions in which thermal energy is used to produce hydrogen and oxygen from water vapor in the presence of a thermochemical material. Thus, the overall reaction of one thermochemical cycle is equivalent to the direct thermal water decomposition since the only substance consumed in the process is water, and the thermochemical material is regenerated after every cycle. ,, The main advantages of WSTCs over the direct thermal water decomposition are (a) the reduction of the operating temperature to 500–1800 °C and (b) not requiring downstream hydrogen and oxygen separation since they are released in different reaction steps. , …”