A large entropy of reduction is crucial in achieving materials capable of high-efficiency solar thermochemical hydrogen (STCH) production through two-step thermochemical water splitting cycles. We have recently demonstrated that the onsite electronic entropy of reduction attains an extreme value of 4.26 kB at 1500 K in Ce4+ → Ce3+ redox reactions, which explains the high performance and uniqueness of CeO2 as an archetypal STCH material. However, ceria requires high temperatures (T > 1500 °C) to achieve a reasonable reduction extent because of its large reduction enthalpy, which is a major obstacle in practical applications. Therefore, new materials with a large entropy of reduction and lower reduction enthalpy are required. Here, we perform a systematic screening to search for Ce4+-based oxides which possess thermodynamics superior to CeO2 for STCH production. We first search the Inorganic Crystal Structure Database (ICSD) and literature for Ce4+-based oxides and subsequently use density functional theory to compute their reduction enthalpies (i.e., oxygen vacancy formation energies). Here, we find that CeTi2O6 with the brannerite structure is the most promising candidate for STCH because it possesses three essential characteristics of an STCH material: (i) a smaller reduction enthalpy compared to ceria yet large enough to split water, (ii) a high thermal stability, as reported experimentally, and (iii) a large entropy of reduction associated with Ce4+ → Ce3+ redox. Our proposed design strategy suggests that further exploration of Ce4+ oxides for STCH production is warranted.
Naghavi, S. Shahab, et al. "CeTi<sub>2</sub>O<sub>6</sub>—A Promising Oxide for Solar Thermochemical Hydrogen Production." ACS Applied Materials and Interfaces, vol. 12, no. 19, Apr. 2020. https://doi.org/10.1021/acsami.0c01083
Naghavi, S. Shahab, He, Jiangang, & Wolverton, C. (2020). CeTi<sub>2</sub>O<sub>6</sub>—A Promising Oxide for Solar Thermochemical Hydrogen Production. ACS Applied Materials and Interfaces, 12(19). https://doi.org/10.1021/acsami.0c01083
@article{osti_1985161,
author = {Naghavi, S. Shahab and He, Jiangang and Wolverton, C.},
title = {CeTi<sub>2</sub>O<sub>6</sub>—A Promising Oxide for Solar Thermochemical Hydrogen Production},
annote = {A large entropy of reduction is crucial in achieving materials capable of high-efficiency solar thermochemical hydrogen (STCH) production through two-step thermochemical water splitting cycles. We have recently demonstrated that the onsite electronic entropy of reduction attains an extreme value of 4.26 kB at 1500 K in Ce4+ → Ce3+ redox reactions, which explains the high performance and uniqueness of CeO2 as an archetypal STCH material. However, ceria requires high temperatures (T > 1500 °C) to achieve a reasonable reduction extent because of its large reduction enthalpy, which is a major obstacle in practical applications. Therefore, new materials with a large entropy of reduction and lower reduction enthalpy are required. Here, we perform a systematic screening to search for Ce4+-based oxides which possess thermodynamics superior to CeO2 for STCH production. We first search the Inorganic Crystal Structure Database (ICSD) and literature for Ce4+-based oxides and subsequently use density functional theory to compute their reduction enthalpies (i.e., oxygen vacancy formation energies). Here, we find that CeTi2O6 with the brannerite structure is the most promising candidate for STCH because it possesses three essential characteristics of an STCH material: (i) a smaller reduction enthalpy compared to ceria yet large enough to split water, (ii) a high thermal stability, as reported experimentally, and (iii) a large entropy of reduction associated with Ce4+ → Ce3+ redox. Our proposed design strategy suggests that further exploration of Ce4+ oxides for STCH production is warranted.},
doi = {10.1021/acsami.0c01083},
url = {https://www.osti.gov/biblio/1985161},
journal = {ACS Applied Materials and Interfaces},
issn = {ISSN 1944-8244},
number = {19},
volume = {12},
place = {United States},
publisher = {American Chemical Society (ACS)},
year = {2020},
month = {04}}
Northwestern University, Evanston, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Fuel Cell Technologies Office
Grant/Contract Number:
EE0008089; AC02-05CH11231
OSTI ID:
1985161
Alternate ID(s):
OSTI ID: 1799432
Journal Information:
ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Journal Issue: 19 Vol. 12; ISSN 1944-8244
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 368, Issue 1923https://doi.org/10.1098/rsta.2010.0114