Criteria for the Efficiency, Stability, and Capacity of Abiotic Photochemical Solar Energy Storage Systems

Abstract

The utilization of simple photochemical reactions for the storage of solar energy in the form of chemical energy in energy-rich products has often been considered in the further development and improvement of e. g. simple thermosolar techniques. The hitherto proposed criteria for the qualification of an abiotic photochemical system are, however, mostly of a qualitative nature, so a mutal comparison of the systems is not precise enough. In this article it is shown how a useful correlation on the basis of time-independent experimental data can be achieved and how, from the viewpoint of photochemistry, a comparative classification of known reactions is possible. The following reactions are compared: the [2 + 21-photocycloadditions of norbornadiene, dimethyl 2,3-norbornadienedicarboxylate, and dicyclopentadienone, the photoisomerization of trans-to cis-diacetylindigo, the photodissociation of nitrosyl chloride as well as a photocatalytic redox reaction. The quantity of material required and storage efficiency are by far the most favorable in the case of trans-diacetylindigo. The main disadvantage of the latter however, is that the energy-rich cis-form rapidly reverts to the stable frans-form at elevated temperatures

Dissociative and Photochemical Mechanisms of Intramolecular Tautomerism

“…The properties of these compounds meet the necessary requirements of the photochemical systems needed to convert the Sun's energy into low-temperature thermal energy [48,[51][52][53][54], namely (1) The initial substance (XVlIa) possesses intensive absorption band with the wavelength Amax = 425 nm, which ensures fairly effective utilization of the solar radiation. 6.3 and 6.4a provide for a possible transformation and storage of light, including solar energy in the form of strain energy of the metastable isomer XVlIb.…”

Photoisomerization of N,N′-disubstituted indigos. A search for energy storage

“…The practical efficiency of the process has been discussed also (39). It appears that one of the disadvantages of the system overcomes its advantages, the main drawback being the low amount of the stored energy: 34 kJ mol-I for N,N1-diacetyl indigo 1, and from 14 to 24 kJ mol-' for various N,N1-dibenzoyl derivatives (1 1, 39).…”

Solar energy storage reactions involving metal complexes

“…Several authors have discussed [1][2][3] the factors limiting the performance of a photochemical energy storage system: First, the chromophore must absorb light of relatively low energy in order to make use of a significant portion of the solar spectrum. Second, the excited state formed on absorption of light must undergo subsequent reactions with high probability.…”

“…We will deal here with two general types of energy storage schemes: photoisomerization, in which the endergonic reaction X±Y (2) is carried out photochemically and the high-energy product Y is stored; and photoredox, where X*, or a species formed from it, undergoes an electron transfer reaction. The photoredox experiments have been designed almost exclusively with the goal of promoting reactions such as H20 -H2 + 1/2 02 .…”

“…(3)] would reduce transportation problems and make the stored energy available in many forms [17]. An artificial chemical system could in principle improve on natural photosynthesizers: although the energy storage process in plants has an efficiency of 6 to 8% [2], much of the stored energy is then used in metabolism. We discuss here three general ways in which transition-metal complexes have been used in photoredox reactions.…”