Smart Materials and Devices for Energy Saving and Harvesting

1. Introduction

The decarbonisation objectives set for 2050 compel us to envisage any effective strategy in order to reduce the human impact on the planet, drastically reducing greenhouse gas emissions to reduce the effects of global warming [1]. To keep the latter to no more than 1.5 °C (as stated by the Paris Agreement), emissions need to be reduced by 45% by 2030 and reach net zero by 2050 [2]. In this urgent process, on the one hand, we will have to rapidly replace fossil energy sources with renewable ones; on the other hand, it will be essential to improve the efficiency of systems and processes to reduce the energy consumption required. Energy harvesting and energy saving by means of novel materials and technologies represent an intriguing challenge for researchers worldwide. In this roadmap, smart materials may play a pivotal role, providing unprecedented performances and properties, as well as the chance to enhance design opportunities and energy saving either in the fabrication process or in operation. Smart materials are defined as highly engineered materials that respond intelligently to their environment with specialized performance to meet specific users’ needs in a reversible fashion. Several classes of materials and devices have been proposed so far, showing highly adaptive properties, such as shape memory materials; piezoelectric materials; chromogenics; new materials for more efficient solar energy conversion; electro-active polymers for energy harvesting, to cite some.

2. An Overview of Published Articles

George Syrrokostas et al. proposed the study (contribution 1) of hybrid electrochromic devices with an iodide/triiodide (I⁻/I₃⁻) redox couple. The application of 1 V was sufficient to achieve a contrast ratio of 8:1 in a time of about 5 min. The authors also proposed a new method for calculating the loss current and clarified the calculation method for coloration efficiency.

Minzhi Ye proposed a study (contribution 2) to optimize the design of a suspended open-type ceiling radiant cooling panel with a curved and segmented structure to enhance heat transfer. The cooling capacity and heat transfer coefficient of the ceiling radiant cooling panel were investigated using a three-dimensional CFD model. Eventually, they found that the cooling capacity and heat transfer coefficient tend to rise with increasing curvature radius and decreasing curvature width.

Dariusz Obracaj presented a work (contribution 3) dealing with heat stress in deep hot mines acting as a practical limiting factor in the mining of natural resources. This research group studied the dewatering system of the mine; they observed that water flow from the mine dewatering system may be used to effectively reject heat in compressor chillers in underground refrigeration plants.

Paulo Santos and co-authors (contribution 4) studied thermal break strips for steel studs’ flanges to mitigate thermal bridges. A validated bidimensional numerical model was adopted, finding that a key parameter is represented by the thickness of thermal break strips.

Andrea Rocchetti et al. investigated the use of metal–organic framework materials to improve the energy efficiency of HVAC systems (contribution 5). In fact, such materials may be exploited to reduce the latent load due to the moisture content in airflows. A psychrometric transformation consisting of cooling and dehumidification was studied for a HVAC system embodying metal–organic framework materials; an energy saving of 30–50% was estimated (in the location of Florence, Italy) compared to a traditional system.

The contribution by Xinhan Qiao and co-authors (contribution 6) deals with the aging of polymeric insulators under various environmental conditions. Silicone rubber indeed tends to lose its initial insulation characteristics, affecting the safety and reliability of the whole power system. In this review paper, several aging and characterization techniques of the polymeric insulators and their aging performance under the action of multiple factors are described.

Chenjue Wang et al. (contribution 7) proposed a new design for a sorption-selective catalytic reduction system to improve ammonia storage density and meet the ammonia demand for high NO_x conversion efficiency at relatively lower temperatures compared to other existing systems.

Zhuyong Li’s work (contribution 8) investigated superconducting multi-stage cables, showing higher transmission power and lower energy loss at the same time. In this work, it was observed that the twisted structure of cables reduces the AC loss by up to 80%, compared with the thin strip model.

Minseon Kong co-authored a paper (contribution 9) regarding the performance of dye-sensitized solar cells embodying a solid-state redox mediator based on an ionic liquid and hole-transporting triphenylamine compound. The resulting mediator was used in several devices, reporting a short circuit current density of 4.61 mA/cm² and a photovoltaic conversion efficiency of 1.80%. A further increase in the electric parameters of these cells was observed due to the addition of 4-tert butylpyridine.

The paper by Jakub Bernat et al. (contribution 10) deals with the design improvement of dielectric electroactive polymer actuators by assuming modifications in the shape of the actuators. Generally, circular shapes are used; however, in this work, the authors investigated the properties of elliptical shapes in dielectric electroactive polymer actuators. Finite element modeling of the actuators was carried out and an experimental comparison validated the results obtained, showing that the elliptical shape of the actuators allows for a wider range of movement.

Alessandro Cannavale and co-authors reviewed the state of the art of building integrated radiative coolers (contribution 11), with the aim of quantifying the effectiveness of radiative systems applied to the construction sector, with special reference to their operation during daytime.

3. Conclusions

This compilation of articles encompasses a diverse range of research, spanning from innovative photovoltaic cells to electroactive polymer actuators, aging of polymeric insulators, metal–organic framework materials to improve the energy efficiency of HVAC systems and other topics that elucidate the richness of the research field regarding smart materials and devices for energy saving and harvesting.