Materials Design Directions for Solar Thermochemical Water Splitting

Wexler, Robert B.; Stechel, Ellen B.; Carter, Emily A.

doi:10.1002/9781119752097.ch1

Cited by 5 publications

(4 citation statements)

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“…Given that CeO 2 is the prototypical oxide for STCH, the observation of high reduction enthalpies up to 5 eV has certainly influenced the common belief that suitable defect formation energies Δ H D ref for thermochemical hydrogen production lie in a range of about 2–5 eV. ,, This wide range essentially reflects a corresponding wide range of associated reduction entropies and, therefore, can be narrowed down by making assumptions about δ S r . , However, the exceptionally large entropies in CeO 2 have so far not been replicated in other STCH oxides, and the upper end of the enthalpy range may be entirely unsuitable for STCH in systems that do not exhibit the high-entropy behavior of CeO 2 . Therefore, it is highly desirable to identify the signatures of ceria-like behavior in the thermochemical properties.…”

Section: Resultsmentioning

confidence: 99%

“…12,20,21 This wide range essentially reflects a corresponding wide range of associated reduction entropies and, therefore, can be narrowed down by making assumptions about δS r . 47,48 However, the exceptionally large entropies in CeO 2 have so far not been replicated in other STCH oxides, and the upper end of the enthalpy range may be entirely unsuitable for STCH in systems that do not exhibit the high-entropy behavior of CeO 2 . Therefore, it is highly desirable to identify the signatures of ceria-like behavior in the thermochemical properties.…”

Section: Resultsmentioning

confidence: 99%

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Chemical Potential Analysis as an Alternative to the van’t Hoff Method: Hypothetical Limits of Solar Thermochemical Hydrogen

Lany

2024

J. Am. Chem. Soc.

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The van’t Hoff method is a standard approach for determining reaction enthalpies and entropies, e.g., in the thermochemical reduction of oxides, which is an important process for solar thermochemical fuels and numerous other applications. However, by analyzing the oxygen partial pressure pO2, e.g., as measured by thermogravimetric analysis (TGA), this method convolutes the properties of the probe gas with the solid-state properties of the examined oxides, which define their suitability for specific applications. The “chemical potential method” is here proposed as an alternative. Using the oxygen chemical potential ΔμO instead of pO2 for the analysis, this method does not only decouple gas-phase and solid-state contributions but also affords a simple and transparent approach to extracting the temperature dependence of the reduction enthalpy and entropy, which carries important information about the defect mechanism. For demonstration of the approach, this work considers three model systems; (1) a generic oxide with noninteracting, charge-neutral oxygen vacancy defects, (2) Sr0.86Ce0.14MnO3(1−δ) alloys with interacting vacancies, and (3) a model for charged vacancy formation in CeO2, which reproduces the extensive experimental TGA data available in the literature. The reduction behavior of these model systems obtained from the chemical potential method is correlated with simulated results for the thermochemical water splitting cycle, highlighting the exceptional behavior of CeO2, which originates from defect ionization. The theoretical performance limits for solar thermochemical hydrogen within the charged defect mechanism are assessed by considering hypothetical materials described by a variation of the CeO2 model parameters within a plausible range.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Chemical Potential Analysis as an Alternative to the van’t Hoff Method: Hypothetical Limits of Solar Thermochemical Hydrogen

Lany

2024

J. Am. Chem. Soc.

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“…2(b)). 19 To quantify the macroscopic reducibility of CCTM2112, we calculate the ensemble-averaged E v , , where f i is the frequency of the i th unique NN V O environment given in Fig. 2(a), and .…”

Section: Resultsmentioning

confidence: 99%

“…For materials that undergo reduction via oxygen off-stoichiometry like CeO 2 and metal-oxide perovskites, V O formation energies ( E v ) of 3.4–3.9 eV correspond to optimal values of Δ H red . 19 The E v of CeO 2 is too high (4.4 eV), 4 hence the need for the design of off-stoichiometry metal oxides like oxide perovskites with a lower E v . Here, we build on our previous theoretical prediction of Pnma Ca 0.5 Ce 0.5 MnO 3 (CCM) 20 as a promising STCH candidate based on its E v of 3.65–3.96 eV (within the target range 19 ) and investigate a stabilized oxide perovskite with Ca and Ce on the A-site and Ti and Mn on the B-site.…”

Section: Introductionmentioning

confidence: 99%