Tunable Redox Temperature of a Co_3–xMn_xO₄ (0 ≤ x ≤ 3) Continuous Solid Solution for Thermochemical Energy Storage

Abstract

Heat-storage technologies are well suited to improve the energy efficiency of power plants and the recovery of process heat. A good option for high storage capacities, especially at high temperatures, is storing thermal energy by reversible thermochemical reactions. In particular, the Co3O4/CoO and Mn2O3/Mn3O4 redox-active couples are known to be very promising systems. However, cost and toxicity issues for Co oxides and the sluggish oxidation rate (leading to poor reversibility) for Mn oxide hinder the applicability of these single oxides. Considering, instead, binary Co–Mn oxide mixtures could mitigate the above-mentioned shortcomings. To examine this in detail, here, we combine first-principles atomistic calculations and experiments to provide a structural characterization and observe the thermal behavior of novel mixed-metal oxides based on cobalt/manganese metals with the spinel structure Co3–x Mn x O4. We show that novel Co3–x Mn x O4 phases indeed enhance the enthalpy of the redox reactions, facilitate reversibility, and mitigate energy losses when compared to pure metal oxide systems. Our results expand therefore the limited list of currently available thermochemical heat-storage materials and pave the way toward the implementation of tunable redox temperature materials for practical applications.

Fourier-transform infrared and X-ray diffraction analyses of the hydration reaction of pure magnesium oxide and chemically modified magnesium oxide

“…Metal oxides, carbonates, and lithium orthosilicates have been used to conserve thermal energy in the temperature range of 800-1000 C. The energy densities recorded for these materials are higher than those recorded for other CHS materials. [39][40][41][42][43][44] We have focused on Mg(OH) 2 (CHS material) to effectively store thermal energy in the temperature range of 200-300 C. This material can be dehydrated under mild conditions and it exhibits high reversibility. The dehydration reaction of Mg(OH) 2 and the hydration reaction of MgO correspond to the heat storage and output operations, respectively.…”

Free energy of (CoxMn1-x)3O4 mixed phases from machine-learning-enhanced ab initio calculations

“…This implies that entropic contributions to the free energy of the mixed metal oxide phases must be * Corresponding author: natalio.mingo@cea.fr responsible for the stability at finite temperatures [5,6]. It has been suggested that a large number of metastable configurations close in energy to the T =0 K ground state may provide the explanation here [1]. However, the full configuration space of this mixed phase system would require millions of ab initio calculations to study exhaustively, even after discounting symmetrically equivalent structures [1].…”

“…The mixed phase system (Co x Mn 1−x ) 3 O 4 is currently under investigation for applications in next-generation concentrated solar energy storage technologies, which are based on reversible redox reactions of metal oxides [1][2][3]. The motivation of the mixed phase is to attempt to minimize the shortcomings of the pure end members, such as cost and toxicity for Co 3 O 4 , and sluggish oxidation rate and poor reversibility for Mn 3 O 4 [4], by combining them in (Co x Mn 1−x ) 3 O 4 .…”

“…1, all compositions of (Co x Mn 1−x ) 3 O 4 should decompose into the pure phases Co 3 O 4 and Mn 3 O 4 . However, the mixed phases have been successfully synthesized in a number of works [1][2][3]. This implies that entropic contributions to the free energy of the mixed metal oxide phases must be * Corresponding author: natalio.mingo@cea.fr responsible for the stability at finite temperatures [5,6].…”

“…It has been suggested that a large number of metastable configurations close in energy to the T =0 K ground state may provide the explanation here [1]. However, the full configuration space of this mixed phase system would require millions of ab initio calculations to study exhaustively, even after discounting symmetrically equivalent structures [1]. Recent advances in the coupling of artificial intelligence (AI) techniques and materials design are creating new opportunities to tackle this challenge [7][8][9].…”