Thermoresponsive Black VO₂–Carbon Nanotube Composite Coatings for Solar Energy Harvesting

Abstract

Solar energy harvesting is an essential component for a clean and sustainable future energy supply. Hereby, solar–thermal energy conversion is of a significant importance, and the role of absorbing layers is pivotal. Nanoscale design of thermally responsive absorbing nanocomposite coatings is addressed in this study with the objective to tailor the light absorption behavior. While carbon nanotubes (CNTs) act as perfect black absorbers, vanadium dioxide (VO2) shows a semiconductor-to-metal transition (SMT) at 67 °C with an abrupt change in the optical properties. Combining the properties of these two nanometric building blocks is investigated as an approach to design smart black nanocomposite films. The CNTs feature either an upward or a downward thermal emissivity switching across the SMT depending on the morphology of the overgrown VO2 nanolayer. Decorated CNTs with VO2 nanoparticles feature an enhancement of the thermal emissivity above the SMT, whereas VO2-covered CNTs feature a decrease of thermal emissivity when they turn metallic above the SMT. The results were successfully explained by a theoretical model based on effective media approximations. By means of this model, the percolation threshold for the VO2 inclusions was identified. VO2 inclusions below this threshold are mostly confined in small domains, and near/mid-infrared light absorption dominates in the metallic phase as a consequence of the localized surface plasmons’ excitation. Above the percolation threshold, VO2 inclusions form large continuous domains that are more reflective in the metallic phase. The percolation threshold is the result of surface-energy-driven dewetting that can be influenced by the implemented thermal treatment. The developed VO2–CNT nanocomposite films hold appealing properties for the design of smart absorbers for solar energy harvesting and thermal management as well as photothermal actuators.

Flexible and Stretchable Thermoresponsive Display for Multifunctional Device Applications

“…Inorganic systems, for instance, VO 2 , are sensitive to higher heating conditions, which might not occur in a functional device. [13][14][15][16][17][18][19][20] On the other hand, the organic dies, for example, leucodyes, are sensitive to moisture and UV exposure. [21,22] Metal-organic frameworks (MOFs) have been investigated as potential materials for thermoresponsive applications.…”

“…Inorganic systems, for instance, VO 2 , are sensitive to higher heating conditions, which might not occur in a functional device. [ 13–20 ] On the other hand, the organic dies, for example, leucodyes, are sensitive to moisture and UV exposure. [ 21,22 ]…”

CNT-ZnO Core-Shell Photoanodes for Photoelectrochemical Water Splitting

“…Furthermore, the wet chemistry-based synthesis results in composite films where the individual CNTs are not directly attached to the substrates, which is unfavourable for the electron collection. These drawbacks can be addressed using hybrid CVD/ALD for the direct growth of CNTs on the target surface, and their consecutive conformal coverage with functional transition metal oxides [46].…”