Efficient storage of solar and wind power is a challenging tasks still limiting the utilization of these prime but intermittent renewable energy sources. The direct storage of concentrated solar power into renewable fuels via thermochemical splitting of water and carbon dioxide on a redox material is a scalable approach with more than 40% theoretical solar-to-fuel conversion efficiency. Despite progress, there is a lack of earth-abundant redox materials that can provide and maintain high H2 and CO production rates over hundreds of high-temperature cycles [1].
Here, we present a strategy to unlock the use of manganese, the 12th most abundant element in the Earth’s crust, for thermochemical synthesis of solar fuels, achieving superior stability, oxygen exchange capacity, and up to seven times higher mass-specific H2 and CO yield than ceria [2]. We observe that incorporation of a small fraction of cerium ions in the manganese (II,III) oxide crystal lattice drastically increases its oxygen ion mobility, allowing its reduction from oxide to carbide during methane partial oxidation [3]. We demonstrate that the oxide to carbide reaction is highly reversible achieving remarkable CO2 and H2O splitting rates over more than 100 thermochemical cycles. These findings suggest that incorporation of small soluble amounts of cerium in transition metal oxides can enable the utilziation of a large family of low-cost earth-abundant elements for the solar thermochemical synthesis of renewable fuels.
References
1. M. Gao, A. Tricoli et al., Journal of Materials Chemistry A 2016, 4 (24), 9614
2. M. Gao, A.Tricoli et al., Nano Energy 2018, 50, 347
3. M. Gao, A.Tricoli et al., ACS Catalysis 2019, doi.org/10.1021/acscatal.9b03205