Naghavi S Shahab, Emery Antoine A, Hansen Heine A, Zhou Fei, Ozolins Vidvuds, Wolverton Chris
Department of Materials Science and Engineering, Northwestern University, Evanston, IL, 60208, USA.
Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark.
Nat Commun. 2017 Aug 18;8(1):285. doi: 10.1038/s41467-017-00381-2.
Previous studies have shown that a large solid-state entropy of reduction increases the thermodynamic efficiency of metal oxides, such as ceria, for two-step thermochemical water splitting cycles. In this context, the configurational entropy arising from oxygen off-stoichiometry in the oxide, has been the focus of most previous work. Here we report a different source of entropy, the onsite electronic configurational entropy, arising from coupling between orbital and spin angular momenta in lanthanide f orbitals. We find that onsite electronic configurational entropy is sizable in all lanthanides, and reaches a maximum value of ≈4.7 k per oxygen vacancy for Ce/Ce reduction. This unique and large positive entropy source in ceria explains its excellent performance for high-temperature catalytic redox reactions such as water splitting. Our calculations also show that terbium dioxide has a high electronic entropy and thus could also be a potential candidate for solar thermochemical reactions.Solid-state entropy of reduction increases the thermodynamic efficiency of ceria for two-step thermochemical water splitting. Here, the authors report a large and different source of entropy, the onsite electronic configurational entropy arising from coupling between orbital and spin angular momenta in f orbitals.
先前的研究表明，较大的还原态固态熵可提高金属氧化物（如二氧化铈）在两步热化学水分解循环中的热力学效率。在此背景下，氧化物中氧非化学计量比产生的组态熵一直是以往大多数研究的重点。本文我们报道了一种不同的熵源，即由镧系元素f轨道中的轨道角动量和自旋角动量耦合产生的局域电子组态熵。我们发现，所有镧系元素中的局域电子组态熵都相当可观，对于Ce/Ce还原，每个氧空位的局域电子组态熵最大值约为4.7 k。二氧化铈中这种独特且较大的正熵源解释了其在诸如水分解等高温催化氧化还原反应中的优异性能。我们的计算还表明，二氧化铽具有较高的电子熵，因此也可能是太阳能热化学反应的潜在候选材料。还原态固态熵提高了二氧化铈在两步热化学水分解中的热力学效率。在此，作者报道了一种不同且较大的熵源，即由f轨道中的轨道角动量和自旋角动量耦合产生的局域电子组态熵。
