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Issue 12, 2015
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Predicting the solar thermochemical water splitting ability and reaction mechanism of metal oxides: a case study of the hercynite family of water splitting cycles

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Abstract

A screening method is developed to determine the viability of candidate redox materials to drive solar thermal water splitting (STWS) and the mechanism by which they operate using only the reduction enthalpy of the material. This method is applied to the doped-hercynite water splitting cycle, as well as FeAl2O4 and CoAl2O4, materials which have not been previously experimentally demonstrated for STWS. Density functional theory (DFT) calculations of reduction energies coupled with our screening method predict H2 production capacities for iron and cobalt aluminate spinels to be in the order FeAl2O4 > Co0.5Fe0.5Al2O4 > CoAl2O4 with relative H2 production capacity ratios of approximately 1.0 to 0.7 to 2 × 10−4, respectively. Experimental measurements for 1500/1350 °C redox temperatures validate the H2 production capacity predicted by the screening method by demonstrating H2 production ratios of 1.0 to 0.6 to 0. Un-doped hercynite (FeAl2O4) is shown to be a viable STWS material for the first time with a higher H2 production capacity than traditional doped-hercynite materials. Theory and experiments show that redox of the aluminate family of spinel materials operates via an O-vacancy mechanism rather than a stoichiometric one, which is more typical for ferrites. The screening approach is generally useful for predicting the ability of new complex materials to drive STWS and the mechanism by which they operate, thus, providing a method to identify promising new candidate STWS materials.

Graphical abstract: Predicting the solar thermochemical water splitting ability and reaction mechanism of metal oxides: a case study of the hercynite family of water splitting cycles

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Supplementary files

Article information


Submitted
26 Jun 2015
Accepted
19 Oct 2015
First published
22 Oct 2015

Energy Environ. Sci., 2015,8, 3687-3699
Article type
Paper
Author version available

Predicting the solar thermochemical water splitting ability and reaction mechanism of metal oxides: a case study of the hercynite family of water splitting cycles

C. L. Muhich, B. D. Ehrhart, V. A. Witte, S. L. Miller, E. N. Coker, C. B. Musgrave and A. W. Weimer, Energy Environ. Sci., 2015, 8, 3687 DOI: 10.1039/C5EE01979F

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