Abstract
Thermochemical energy storage is promising for the long-term storage of solar energy via chemical bonds using reversible redox reactions. The development of thermally-stable and redox-active materials is needed, as single metal oxides (mainly Co and Mn oxides) show important shortcomings that may delay their large-scale implementation in solar power plants. Drawbacks associated with Co oxide concern chiefly cost and toxicity issues while Mn oxide suffers from slow oxidation kinetics and poor reversibility. Mixed metal oxide systems could alleviate the above-mentioned issues, thereby achieving improved materials characteristics. All binary oxide mixtures of the Mn-Co-Fe-Cu-O system are considered in this study, and their properties are evaluated by experimental measurements and/or thermodynamic calculations. The addition of Fe, Cu or Mn to cobalt oxide decreased both the oxygen storage capacity and energy storage density, thus adversely affecting the performance of Co3O4/CoO. Conversely, the addition of Fe, Co or Cu (with added amounts above 15, 40 and 30 mol%, respectively) improved the reversibility, re-oxidation rate and energy storage capacity of manganese oxide. Computational thermodynamics was applied to unravel the governing mechanisms and phase transitions responsible for the materials behavior, which represents a powerful tool for predicting the suitability of mixed oxide systems applied to thermochemical energy storage.
Highlights
The intermittent nature of solar energy used to drive concentrated solar power (CSP) plants calls for a suitable energy storage system, which will grant us the freedom to produce and dispatch electricity according to the population needs
As for the copper oxide (CuO/Cu2 O), it has been studied for air separation applications [23], but has attracted attention for thermochemical energy storage (TCES) application as it presents high energy storage capacity, 811 kJ/kg [21,25] and the reaction temperature is suitable to be used with CSP [21,22,25]
To cope with the noticeable challenges for developing reliable energy storage materials applied to solar power plants, binary and ternary metal oxide systems are considered
Summary
The intermittent nature of solar energy used to drive concentrated solar power (CSP) plants calls for a suitable energy storage system, which will grant us the freedom to produce and dispatch electricity according to the population needs. As for the copper oxide (CuO/Cu2 O), it has been studied for air separation applications [23], but has attracted attention for TCES application as it presents high energy storage capacity, 811 kJ/kg [21,25] and the reaction temperature is suitable to be used with CSP [21,22,25]. It is possible to achieve better redox performance with a metal oxide by modifying its morphology (for example through tailored synthesis), or through the addition of a secondary transition metal In previous works, this method has been applied to modify single metal oxides, Co3 O4 and Mn2 O3 , and the impacts of this modification on the tuning of reaction kinetics, cycling stability and reaction temperature, were reported [34,35,36]. It relies on existing phase diagrams and thermodynamic models of the ternary systems M-M’-O in air (where M and M’ are two different metals from Co, Mn, Fe and Cu)
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