Using stretchable nanogenerators to obtain disordered mechanical energy from the environment is an ideal way to realize wearable power supply equipment and self-power electronic devices, and alleviate the energy crisis. It is of great significance to integrate the stretchability into the nanogenerator, which can fit the complex shape of the target object better and is well suitable for wearable electronics. When applied to the human body, it can directly harvest human body mechanical energy to power wearable electronic devices and get rid of the trouble of charging. This paper systematically reviewed nanogenerators in stretchability, focusing on stretchable triboelectric nanogenerators, stretchable piezoelectric nanogenerators, and stretchable hybrid nanogenerators. Their physical mechanism, material selection, structure design, and output performance are discussed in detail. It is concluded that the fabrication methods of various devices can be broadly categorized into the two most important device types, namely fiber-like and planar. A detailed analysis of representative work and the latest progress in the past decade is performed. It is most important that excellent stretchability and high-power output are the key point to realize application value of stretchable nanogenerators. In addition, we discuss opportunities and challenges, as well as future development direction of stretchable nanogenerators.

Hydrogen evolution via photo-electro-chemical (PEC) co-catalysis is potential for solving energy crisis and environmental issues. The rapidly advances of fabrication and broad applications of polydopamine (PDA) and its derivatives have drawn intense attentions in recent years. Herein, an ultrathin PDA coating with nanometer accuracy was conformally grown on TiO₂ nanotube arrays (NTAs) via electrochemical polymerization, in which the polymer provided a platform for further photoinduced assembly of CdS nanocrystals in the embedded mode. The optimized CdS@PDA/TiO₂ NTAs hierarchical heterostructure as photoanode gave an excellent PEC performance and exhibited outstanding stability under light irradiation. The photocurrent density was heightened to 5.48 mA·cm^–2, which was beneficial to H₂ evolution with a rate of 20 μmol·h^–1·cm^–2. The improvement of PEC activity was ascribed to co-photosensitization, optimized carriers transfer, and transport route arised from CdS embedding, resulting to provide a persistent driving force for charge separation based on secure heterojunction of CdS/TiO₂ glued by PDA. The improvement of PEC stability was due to the inhibition of CdS photocorrosion covered by PDA shelter. This advance boded well for the development of PEC field founded on multifunctional PDA.

Stretchable strain sensors play an increasingly important role in artificial intelligent devices. However, high-performance strain sensors have been slowly developed owing to the harsh requirement of self-powered function, long cycle life and high resolution. Here, we report a self-powered stretchable graphene-ecoflex composite strain sensor based on photo-thermoelectric (PTE) effect induced electricity. The device exhibits a high strain sensitivity of -0.056 ln(nA)/% with strains ranged from 0% to 20% under 980 nm light illumination, where the strain sensitivity can be found to increase with increasing light intensity. The strain sensor maintains outstanding dynamic stability under periodic strains ranged from 0 to 100% in 100 cycles. The sensing resolution can be as high as 0.5% with both the response and recovery time of less than 0.6 s. It can precisely monitor human joint motions and stretchable strains by implanting the device in pork.

We propose a fully enclosed hybrid nanogenerator consisting of five electromagnetic generators (EMGs) and four triboelectric nanogenerators (TENGs). Under a vibration frequency of 15.5 Hz, one TENG can deliver a high output voltage of approximately 24 V and a low output current of approximately 24 μA, whereas one EMG can deliver a low output voltage of approximately 0.8 V and a high output current of approximately 0.5 mA. By integrating five rectified EMGs in series and four rectified TENGs in parallel, the hybrid nanogenerator can be used to charge a home-made Li-ion battery from 1 to 1.9 V in 6.3 h. By using the hybrid nanogenerator to scavenge the vibrational energy produced by human hands, a temperature–humidity sensor can be sustainably powered by the nanogenerator, which is capable of charging the 200 μF system power capacitor from 0 to 2 V in 15 s, and sustainably power the sensor in 29 s.

Utilizing a nanogenerator to scavenge mechanical energy from our living environment is an effective method to solve the power source issue of portable electronics. We report a linear-grating hybridized electromagnetic-triboelectric nanogenerator for scavenging the mechanical energy generated from sliding motions to sustainably power certain portable electronics. The hybridized nanogenerator consists of a slider and a stator in the structural design, and possesses a 66-segment triboelectric nanogenerator (TENG) and a 9-segment electromagnetic generator (EMG) in the functional design. At a sliding acceleration of 20 m/s², the hybridized nanogenerator can deliver maximum powers of 102.8 mW for the TENG at a loading resistance of 0.4 MΩ and 103.3 mW for the EMG at a loading resistance of 6 kΩ. With an optimal hybridized combination of the TENG with a transformer and the EMG with a power management circuit, a 10 mF capacitor can be easily charged to 2.8 V in 20 s. A packaged hybridized nanogenerator with a light weight of 140 g and small dimensions of 12 cm × 4 cm × 1.6 cm excels in scavenging low-frequency sliding energy to sustainably power portable electronics.

We report a hybrid nanogenerator that includes a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) for scavenging mechanical energy. This nanogenerator operates in a hybrid mode using both the triboelectric and electromagnetic induction effects. Under a vibration frequency of 14 Hz, the fabricated TENG can deliver an open-circuit voltage of about 84 V, a short-circuit current of 43 μA, and a maximum power of 1.2 mW (the corresponding power per unit mass and volume are 1.82 mW/g and 3.4 W/m³, respectively) under a loading resistance of 2 MΩ, whereas the fabricated EMG can produce an opencircuit voltage of about 9.9 V, a short-circuit current of 7 mA, and a maximum power of 17.4 mW (the corresponding power per unit mass and volume are 0.53 mW/g and 3.7 W/m³, respectively) under a loading resistance of 2 kΩ. Impedance matching between the TENG and EMG can be achieved using a transformer to decrease the impedance of the TENG. Moreover, the energy produced by the hybrid nanogenerator can be stored in a home-made Li-ion battery. This research represents important progress toward practical applications of vibration energy generation for realizing self-charging power cells.

We report a hybrid energy cell that can simultaneously or individually harvest wind, solar, and chemical energies to power some electronic devices. By utilizing the wind driven relative rotations between a polytetrafluoroethylene film and an etched Al film attached on two acrylic tubes, the fabricated triboelectric nanogenerator (TENG) can deliver an open-circuit voltage of about 90 V, a short-circuit current density of about 0.5 mA/m², and a maximum power density of 16 mW/m², which is capable of directly lighting up 20 blue light-emitting-diodes (LEDs). By integrating a TENG, a solar cell, and an electrochemical cell, a hybrid energy cell has been fabricated to simultaneously scavenge three different types of energies. As compared with the individual energy units, the hybrid energy cell exhibited much better performance in charging a capacitor. Moreover, we also demonstrated that the hybrid energies generated can be stored in a Li-ion battery for powering a commercial wind speed sensor and a temperature sensor. This work represents significant progress toward practical applications of hybrid energy cells, providing potential solutions for simultaneously scavenging wind, solar, and chemical energies.