Solar hydrogen production using Ce1−Li O2− solid solutions via a thermochemical, two-step water-splitting cycle

Meng, Qing-Long; Lee, Chong-il; Shigeta, S.; Kaneko, Hiroshi; Tamaura, Yutaka

doi:10.1016/j.jssc.2012.05.024

Cited by 44 publications

(27 citation statements)

References 32 publications

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“…Among the dopants, we rst discuss Zr and Hf tetravalent dopants which aid the redox performance, 24,30,[32][33][34] before discussing those dopants which do not, i.e. di-, tri-, Ti-, and pentavalent dopants, 16,20,[23][24][25][26][27][28][29][30][31] in that order. In each case, we investigated the elements from periodic table rows 4, 5, and 6, and detail the row 5 elements and then compare the row 4 and 6 elements to the exemplar.…”

Section: Resultsmentioning

confidence: 99%

“…Di-, tri-and pentavalent dopants, including Li, Mg, Cu, Zn, Sr, Al, Sc, Cr, Mn, Fe, Co, Ni, Y, La, Pr, Sm, Gd, and Ta provide little, if any, improvement in the H 2 production capacity of ceria, although some prevent sintering and grain growth. 16,20,[23][24][25][26][27][28][29][30][31] Tetravalent Zr and Hf, however, have been shown to signicantly improve the redox capacity of ceria. 24,30,[32][33][34] To date the selection of dopants for STWS is mostly based on trial and error; therefore, we attempt to bring an understanding of ceria dopants to the STWS community.…”

Section: Oxidationmentioning

confidence: 99%

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Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂

Muhich

Steinfeld

2017

J. Mater. Chem. A

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Ceria-based metal oxides are promising redox materials for solar H 2 O/CO 2 -splitting thermochemical cycles. Density functional theory (DFT) computations are applied to elucidate the underlying mechanism of the role of dopants in facilitating ceria based redox cycles; specifically, we explain why some dopants increase performance, while others do not. Firstly, we find that Zr and Hf dopants increase the oxygen exchange capacity of ceria because they store energy in tensilely strained Zr-or Hf-O bonds which is released upon O-vacancy formation. This finding corrects a long held assumption that Zr and Hf decrease the O-vacancy formation energy by compensating for ceria expansion upon reduction.Although the released strain energy decreases the O-vacancy formation energy, O-vacancy formation remains sufficiently endothermic to split H 2 O and CO 2 . Secondly, we show that two electrons must be promoted into the high energy Ce f-band during reduction if the O-vacancies are to store sufficient energy to drive the oxidative gas splitting step. This means that di-and trivalent dopants are not suitable for this process. Lastly, we show that dopants which break O bonds due to their small size or strongly covalent character, such as Ti and the pentavalent dopants, substantially decrease the O-vacancy formation energy because only three O bonds must break during reduction. These vacancies, therefore, are too low in energy to drive gas splitting. Based on these findings, we develop guidelines for new ceria doping strategies to facilitate solar thermochemical gas splitting cycles.

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Section: Resultsmentioning

confidence: 99%

Section: Oxidationmentioning

confidence: 99%

Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂

Muhich

Steinfeld

2017

J. Mater. Chem. A

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“…Many elements have been doped into ceria in an attempt to increase the H 2 production and lower the required reduction temperature. Divalent (Li, Mg, Cu, Zn, Sr) and trivalent (Al, Sc, Cr, Mn, Fe, Co, Ni, Y, La, Pr, Sm, Gd, Ta) dopants have not achieved these goals. The divalent and trivalent elements decrease the oxygen vacancy formation enthalpy to such an extent that the oxygen vacancies no longer possess the energy required to split water.…”

Section: Two‐step Stws Active Materialsmentioning

confidence: 99%

A review and perspective of efficient hydrogen generation via solar thermal water splitting

Muhich

Ehrhart

Al‐Shankiti

et al. 2015

WIREs Energy & Environment

195

160

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Solar thermal water splitting (STWS) produces renewable hydrogen from water using concentrated sunlight. Because it utilizes energy from the entire solar spectrum to directly drive the redox reactions that split water, it can achieve high theoretical solar-to-hydrogen efficiencies. In two-step STWS, a metal oxide is first heated by concentrated sunlight to high temperatures to reduce it and produce O 2 . In the second step, the reduced material is exposed to H 2 O to reoxidize it to its original oxidation state and produce H 2 . Various aspects of this process are reviewed in this work, including the reduction and oxidation chemistries of the active redox materials, the effects of operating conditions, and the solar thermal reactors in which the STWS reactions occur, and a perspective is given on the future optimization of STWS.

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“…A plethora of dopants, basically lanthanides and alkaline earths, has been tested to improve the redox/thermal stability characteristics [38,125,[133][134][135][136]. A consensus on the beneficial effect ofanyway well-known from automotive emission control catalysts [137,138] -blending of CeO 2 with ZrO 2 with additions of La 2 O 3 to induce thermal stability seems to having been established [38,128,139].…”

Section: The Ceria Cyclementioning

confidence: 99%

A review on solar thermal syngas production via redox pair-based water/carbon dioxide splitting thermochemical cycles

Agrafiotis

Roeb

Sattler

2015

Renewable and Sustainable Energy Reviews

349

151

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Solar hydrogen production using Ce1−Li O2− solid solutions via a thermochemical, two-step water-splitting cycle

Cited by 44 publications

References 32 publications

Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂

Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂

A review and perspective of efficient hydrogen generation via solar thermal water splitting

A review on solar thermal syngas production via redox pair-based water/carbon dioxide splitting thermochemical cycles

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Solar hydrogen production using Ce1−Li O2− solid solutions via a thermochemical, two-step water-splitting cycle

Cited by 44 publications

References 32 publications

Principles of doping ceria for the solar thermochemical redox splitting of H2O and CO2

Principles of doping ceria for the solar thermochemical redox splitting of H2O and CO2

A review and perspective of efficient hydrogen generation via solar thermal water splitting

A review on solar thermal syngas production via redox pair-based water/carbon dioxide splitting thermochemical cycles

Contact Info

Product

Resources

About

Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂

Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂