Solar–Thermal Fuels and the Role of Carbon Nanomaterials: A Perspective with Emphasis on the Azobenzene System

Abstract

Molecular switches have long been investigated aiming at developing sustainable and renewable energy-based technologies. Among molecular photoswitches, azobenzene (AB) has been the quintessential template for solar−thermal fuels (STFs), acting as "molecular batteries", storing and discharging energy by converting between its trans-and cis-isomers upon absorption of UV light. Nevertheless, key properties for device performance such as stored energy, energy density, stability of the "charged" metastable isomer, or the control of energy release are highly influenced by a mediating interface. This has motivated the study of metal and carbon nanomaterials as templates in hybrid STFs. The latter have been shown to be especially promising owing to their unique electronic properties, topological tailoring, and abundant sourcing. This review discusses recent advances that explore enhancements on several molecular photoswitch systems, with a special emphasis on the AB system, associated with changes in the molecular substituents and the development of hybrid systems, involving mainly carbon nanotemplates, such as reduced graphene oxide, graphene, carbon nanotubes, and fullerenes. The energy density, τ 1/2 , grafting density, and charge transfer of the AB and the hybrid adsorbed AB system on carbon nanomaterials are discussed. Key facets of the design of hybrid STF devices are discussed, along with a perspective on the aspects that merit further investigation toward the development of efficient STFs.

Multichromophoric photoswitches for solar energy storage: from azobenzene to norbornadiene, and MOST things in between

“…There is various emerging research into azobenzene-grafted polymers, azobenzene-functionalised carbon nanomaterials, 7,64,65 and also the use of nanoparticles 66,67 to enhance solar thermal energy storage. Kolpak et al used DFT to investigate different carbon-based templates in combination with various azobenzene photoswitches as potential chromophore/nanostructure hybrids for customizable energy storage applications.…”

“…Several approaches of breaking the conjugation between para-bisazobenzenes have been presented, 62 though in order to achieve multistate switching, differently substituted azobenzene units must be incorporated, resulting in more complex designs; multiphotochromic azobenzene compounds that can be addressed selectively are still exceptional. 63 There is various emerging research into azobenzene-graed polymers, azobenzene-functionalised carbon nanomaterials, 7,64,65 and also the use of nanoparticles 66,67 to enhance solar thermal energy storage. Kolpak et al used DFT to investigate different carbon-based templates in combination with various azobenzene photoswitches as potential chromophore/ nanostructure hybrids for customizable energy storage applications.…”

Optimizing the performance of phase-change azobenzene: from trial and error to machine learning

“…A major limitation is the difficulty in fully elucidating the relationship between the structure and performance, often resulting in low energy storage density within a limited temperature range. 71 During the last few years, researchers have conducted numerous studies on the factors that affect isomerization and phase change processes, and some notable results have been obtained. With advancements in information technology, machine learning (ML) and artificial intelligence (AI) have begun to revolutionize molecular design.…”

“…A major limitation is the difficulty in fully elucidating the relationship between the structure and performance, often resulting in low energy storage density within a limited temperature range. 71…”

Spatiotemporal Utilization of Latent Heat in Erythritol‐based Phase Change Materials as Solar Thermal Fuels

“…STFs can capture, convert, and store solar irradiation energy and release the stored energy as heat on demand [6–9] . Currently, a major part of the attention is focused on the design and engineering of photoactive molecules that can undergo reversible photoinduced isomerization upon light irradiation as the process of “charge” and “discharge” of energy [3,10] . However, these molecular STFs still face challenges when it comes to practical applications.…”