Abstract
The dihydroazulene/vinylheptafulvene (DHA/VHF) thermocouple is a promising candidate for thermal heat batteries that absorb and store solar energy as chemical energy without the need for insulation. However, in order to be viable the energy storage capacity and lifetime of the high energy form (i.e., the free energy barrier to the back reaction) of the canonical parent compound must be increased significantly to be of practical use. We use semiempirical quantum chemical methods, machine learning, and density functional theory to virtually screen over 230 billion substituted DHA molecules to identify promising candidates. We identify a molecule with a predicted energy density of 0.38 kJ/g, which is significantly larger than the 0.14 kJ/g computed for the parent compound. The free energy barrier to the back reaction is 11 kJ/mol higher than the parent compound, which should correspond to a half-life of about 10 days—4 months. This is considerably longer than the 3–39 h (depending on solvent) observed for the parent compound and sufficiently long for many practical applications. Our paper makes two main important contributions: (1) a novel and generally applicable methodological approach that makes screening of huge libraries for properties involving chemical reactivity with modest computational resources, and (2) a clear demonstration that the storage capacity of the DHA/VHF thermocouple cannot be increased to >0.5 kJ/g by combining simple substituents.
Highlights
The Sun is the most abundant source of energy, but periods of supply do not always match periods of demand
The goal of this study is to identify substituted DHAs with both higher energy density and longer half life through high throughput virtually screening
The goal of this study is to identify molecules with an energy storage density that is as high as possible and a half-life of that is at least as long as the parent compound and preferably longer
Summary
The Sun is the most abundant source of energy, but periods of supply do not always match periods of demand. Finding solutions for storing solar energy is one of the major challenges for a sustainable society. A molecule is converted to a high-energy photo-isomer and upon a certain stimulus, the high-energy isomer returns to the original molecule, and the excess energy is released as heat. This corresponds to a closed energy cycle of light-harvesting, How to cite this article Koerstz M, Christensen AS, Mikkelsen KV, Nielsen MB, Jensen JH. High throughput virtual screening of 230 billion molecular solar heat battery candidates.
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