Comparative Assessment of Solar Thermal Water Splitting Materials

Tran, J. T., Oregon State University
Weimer, A. W., University of Colorado Boulder
Warren, K. J., University of Colorado Boulder
Hydrogen is a clean energy source that can replace fossil fuels in the transportation and power sectors, two of the largest contributors of anthropogenic greenhouse gas emissions. Globally, more than 95% of hydrogen is produced from fossil fuels, resulting in CO2 emissions and a significant carbon footprint. To address this, researchers have sought to produce hydrogen via solar thermal water splitting (STWS) using solar energy to drive the endothermic water splitting reaction via a reduction/oxidation cycle. Cerium (IV) oxide, or ceria, CeO2 has demonstrated benchmark performance for STWS because it exhibits excellent thermal stability and fast redox kinetics. However, meaningful hydrogen productivities are only observed following reduction at temperatures above 1500°C, which are too high for commercial realization. Alternatively, perovskites have demonstrated water splitting at more suitable temperatures but have shown either lower rates or productivity as compared to ceria.

This study looks to compare different STWS materials and evaluate their performance under various operating conditions. Ceria and various perovskites (SLMA SrxLa1-xMnyAl1-yO3, BCM BaCe0.25Mn0.75O3, CSM CexSr2-xMnO4, LSCM La0.6Sr0.4CrxMn1-xO3) were tested in a stagnation flow reactor. Materials are compared by evaluating their hydrogen production capacity and water consumed to hydrogen produced (H2O:H2) ratio. Results show that ceria and LSCM have low productivities, but fast kinetics while SLMA, BCM, CSM produce more hydrogen but over longer oxidation times for the conditions tested, showing a tradeoff between productivity and kinetics. A direct comparison provides researchers with a path forward to ensure that STWS is competitive with other hydrogen production technologies.