2.a Zinc Oxide-Based Rotational–Linear Triboelectric Nanogenerator

We developed a prototype energy-harvesting device that converts rotational motion into linear motion to harvest rotational energy. Triboelectric materials are affixed to the moving parts responsible for linear motion, enabling a contact-separation mode of triboelectric generator operation. Thin layers of ZnO nanoparticles deposited on Kapton films were evaluated as the triboelectric material. The rotational–linear triboelectric nanogenerator (RL-TENG) design offers several advantages, including avoidance of wear and elevated temperatures typical of rotational tribogenerators. Our approach also supports a modular design for energy-harvesting devices across a range of applications. As a demonstrator, cups were attached to the RL-TENG’s rotating axis to harvest wind energy, demonstrating suitability for maritime applications (A. Bardakas et al., “Zinc Oxide-Based Rotational–Linear Triboelectric Nanogenerator,” Appl. Sci., vol. 14, no. 6, p. 2396, Mar. 2024, doi: 10.3390/app14062396).

2.b Influence of SiC and ZnO Doping on the Electrical Performance of Polylactic Acid-Based Triboelectric Nanogenerators

Polylactic acid (PLA) is among the most widely used materials for fused deposition modeling (FDM) 3D printing. It is a biodegradable thermoplastic polyester derived from natural resources such as corn starch or sugarcane, with low environmental impact and good mechanical properties. A key feature of PLA is that its properties can be tuned by incorporating nanofillers. We investigated the influence of SiC and ZnO doping of PLA on the triboelectric performance of PLA-based tribogenerators. Our results show that the triboelectric signal in ZnO-doped PLA composites increases with higher ZnO concentrations, achieving a 741% enhancement in output power at 3 wt% ZnO. SiC-doped PLA behaves differently: the triboelectric signal initially rises, reaching a peak and an output power increase of 284% compared with undoped PLA at 1.5 wt% SiC. However, increasing the SiC content to 3 wt% significantly reduces the triboelectric signal to levels comparable to or lower than undoped PLA. These trends are consistent with recent findings for PVDF doped with silicon carbide nanoparticles and are attributed to a reduction in the contact area between the triboelectric surfaces (S. Skorda et al., “Influence of SiC and ZnO Doping on the Electrical Performance of Polylactic Acid-Based Triboelectric Nanogenerators,” Sensors, vol. 24, no. 8, p. 2497, Apr. 2024, doi: 10.3390/s24082497).

2.c ZnO based piezoelectric generators

Vibrational energy scavenging using low-dimensional piezoelectric elements has emerged as a promising technique for the energy autonomy of sensors, microsystems and small portable electronic devices. Among these low-dimensional materials, ZnO nanostructures and nanotextured films have become the leading star, demonstrating a new pathway for harvesting energy for self-powered wireless nanodevices and nanosystems. Due to its low fabrication cost at the wafer scale and its applicability to a variety of substrates, low-temperature, user- and-environmentally-friendly all-solution based growth of ZnO nanostructures and nanotextured films has been successfully applied for the development of nanogenerators both on silicon as well on flexible substrates, including PET, Kapton, wax paper and carton.

2.d Thermoelectric generators

Solid state thermoelectric generators are devices that can convert thermal gradients to electrical power through the Seebeck effect. These devices are reliable, low noise and low cost, but suffer from low conversion efficiencies. On the other hand, energy is wasted in the form of heat for a vast variety of everyday situations, ranging from exhaust pipes in cars, to heat generated on a microprocessor to even heat generated by the human body. The harvesting of even a small amount of this wasted energy can be extremely useful in the field of autonomous sensors for IoT applications, for example. More specifically, the use of locally created porous Si (low thermal conductivity material) on a Si substrate (high thermal conductivity material) allows for the creation of temperature differentials on its surface. The use of this temperature differential on a chip level allows the creation of efficient, on-chip thermoelectric generators compatible with standard Si processing.