Electrical energy generation by squeezing a graphene-based aerogel in an electrolyte

Microbial biofilm-based hydrovoltaic technology

Hydrovoltaic electricity generation (HEG) utilizes the latent environmental heat stored in water, and subsequently harvests the electrical energy. However, sustainable HEG has remained extremely challenging due either to complex fabrication and high cost, or to restricted environmental compatibility and renewability. Electroactive microorganisms are environmentally abundant and viable in performing directional electron transport to produce currents. These distinctive features have inspired microbial HEG systems that can convert environmental energy into hygroelectricity upon water circulation from raindrops, waves, and water moisture, and has recently succeeded as proof of concept for becoming a cutting-edge biotechnology. In this review, recent advances in microbial biofilm-based hydrovoltaic technology are highlighted to better understand a promising method of electricity generation from environmental energy with the aim of practical applications.

Strategies for enhancing low-frequency performances of triboelectric, electrochemical, piezoelectric, and dielectric elastomer energy harvesting: recent progress and challenges

Mechanical energy harvesting transforms various forms of mechanical energy, including ocean waves, wind, and human motions, into electrical energy, providing a viable solution to address the depletion of fossil fuels and environmental problems. However, one major obstacle for the direct conversion of mechanical energy into electricity is the low frequency of the majority of mechanical energy sources (≤5 Hz), resulting in low energy conversion efficiency, output power and output current. Over recent years, a numerous innovative technologies have been reported to enable improved energy harvesting utilizing various mechanisms. This review aims to present an in-depth analysis of the research progress in low-frequency energy harvesting technologies that rely on triboelectric, electrochemical, piezoelectric, and dielectric elastomer effects. The discussion commences with an overview of the difficulties associated with low-frequency energy harvesting. The critical aspects that impact the low-frequency performance of mechanical energy harvesters, including working mechanisms, environmental factors, and device compositions, are elucidated, while the advantages and disadvantages of different mechanisms in low-frequency operation are compared and summarized. Moreover, this review expounds on the strategies that can improve the low-frequency energy harvesting performance through the modulations of material compositions, structures, and devices. It also showcases the applications of mechanical energy harvesters in energy harvesting via waves, wind, and human motions. Finally, the recommended choices of mechanical energy harvesters with different mechanisms for various applications are offered, which can assist in the design and fabrication process.

Enhanced energy harvester performance by a tension annealed carbon nanotube yarn at extreme temperatures

Carbon nanotube (CNT) yarns generate electrical energy when they were stretched in an electrolyte, and they have been exploited for diverse applications such as self-powered sensors and human health monitoring systems. Here we improved the capacitance change and harvester performance of a coiled CNT yarn by using an incandescent tension annealing process (ITAP). When undergoing stretching cycles at 1 Hz, a coiled ITAP yarn can produce 2.5 times peak electrical power and 1.6 times output voltage than that of a neat CNT yarn. Electrochemical analysis shows that the capacitance of the ITAP yarn decreased by 20.4% when it was stretched to 30% strain. Microstructure results demonstrate that the large capacitance change may result from the densified electrochemical surface by the ITAP. Moreover, the potential of the zero charge (PZC) of ITAP yarns was shifted to a more negative value than that of the neat CNT yarn, which means that more charges were injected into the ITAP yarn once it was immersed in an electrolyte. Thus, the large capacitance change and initial injected charge are two main reasons for enhancing the harvester performance of the ITAP yarn. In addition, by annealing a twisted CNT yarn before it was coiled, we further increased the output peak power density to 170 W kg^-1 at a strain of 55%.

Ultralight Iontronic Triboelectric Mechanoreceptor with High Specific Outputs for Epidermal Electronics

The pursuit to mimic skin exteroceptive ability has motivated the endeavors for epidermal artificial mechanoreceptors. Artificial mechanoreceptors are required to be highly sensitive to capture imperceptible skin deformations and preferably to be self-powered, breathable, lightweight and deformable to satisfy the prolonged wearing demands. It is still struggling to achieve these traits in single device, as it remains difficult to minimize device architecture without sacrificing the sensitivity or stability. In this article, we present an all-fiber iontronic triboelectric mechanoreceptor (ITM) to fully tackle these challenges, enabled by the high-output mechano-to-electrical energy conversion. The proposed ITM is ultralight, breathable and stretchable and is quite stable under various mechanical deformations. On the one hand, the ITM can achieve a superior instantaneous power density; on the other hand, the ITM shows excellent sensitivity serving as epidermal sensors. Precise health status monitoring is readily implemented by the ITM calibrating by detecting vital signals and physical activities of human bodies. The ITM can also realize acoustic-to-electrical conversion and distinguish voices from different people, and biometric application as a noise dosimeter is demonstrated. The ITM therefore is believed to open new sights in epidermal electronics and skin prosthesis fields.

Graphene Oxide Aerogel Foam Constructed All-Solid Electrolyte Membranes for Lithium Batteries

With the development of electric vehicles and products, lithium metal batteries with solid-state electrolytes have shown a broad application prospect. However, the uneven deposition of lithium, low ion conductivity, narrow electrochemical window, and high interfacial impedance limit the safety and performance of the solid-state batteries. Herein, we develop a non-ceramic solid electrolyte based on the graphene oxide aerogel frame filling with polyethylene oxide (GSPE). The resulting uniform and resilient framework structure form a continuous Li-ion adsorption zone, which ensures uniform ion-current distribution at the interface while obtaining the relatively high ionic conductivity, effectively preventing the uneven deposition of lithium, and thus greatly improving the battery stability. Comprehensive electrochemical analysis showed that GSPE achieved an ionic conductivity of 4.12 × 10^-4 S cm^-1 at 50 °C. The assembled LiFePO₄(LFP) |GSPE| Li full battery can stably cycle for more than 100 cycles at 0.1 C, and the lithium symmetrical battery can continuously be plating-peeling for more than 600 h at 0.1 mA cm^-2. The method of using the carbon aerogel structure to achieve the uniform deposition of lithium ions has explored a new possible research direction for all-solid-state batteries.

N-Doped graphene supported on N-rGO nanosheets as metal-free oxygen reduction reaction electrocatalysts for Zn–air batteries

Metal-free electrocatalysts for the oxygen reduction reaction (ORR) are the desired materials for metal–air batteries.