Crystalline Porous Material-Based Nanogenerators: Recent Progress, Applications, Challenges, and Opportunities.

Nanogenerator (NG) is a potential technology that allows to build self-powered systems, sensors, flexible and portable electronics in the current Internet of Things (IoT) generation. Nanogenerators include piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), convert different forms of mechanical motion into useful electrical signals. They have evolved and expanded their applications in various fields since their discovery in 2006 and 2012. Material selection is crucial for designing efficient NGs, with high conversion efficiencies. In the recent past, crystalline porous mat erials (metal-organic frameworks (MOFs) and covalent organic frameworks (COFs)) have been widely reported as potential candidates for nanogenerators, owing to their special properties of large surface area, porosity tailoring, ease of surface, post-synthesis modification, and chemical stability. The present organized review provides a complete overview of all the crystalline porous materials (CPMs)-based nanogenerator devices reported in the literature, including synthesis, characterization, device fabrication, and potential applications. Additionally, this review article discusses current challenges, future directions, and perspectives in the field of CPMs-NGs.

Carbohydrate-protein interaction-based detection of pathogenic bacteria using a biodegradable self-powered biosensor.

Battery-free and biodegradable sensors can detect biological elements in remote areas. The triboelectric nanogenerator (TENG) can potentially eliminate the need for a battery by simply converting the abundant vibrations from nature or human motion into electricity. A biodegradable sensor system integrated with TENG to detect commonly found disease-causing bacteria (E. coli) in the environment is showcased herein. In this system, D-mannose functionalized 3D printed polylactic acid (PLA) with the brush-painted silver electrode was used to detect E. coli by a simple carbohydrate-protein interaction mechanism. The adsorption capacity of D-mannose is generally altered by varying the concentration of E. coli resulting in changes in resistance. Thus, the presented biosensor can detect bacterial concentrations by monitoring the output current. The PLA TENG generates an output of 70 V, 800 nA, and 22 nC, respectively. In addition, tap water and unpasteurized milk samples are tested for detecting bacteria, and the output is measured at 6 µA and 5 µA, respectively. Further, the biosensor was tested for biodegradability in soil compost by maintaining constant temperature and humidity. This study not only proposes an efficient and fast method for screening E. coli but also gives important insights into the ability to degrade and long-term reliability of TENG-based sensor platforms.

Hybrid Nanogenerators for Ocean Energy Harvesting: Mechanisms, Designs, and Applications.

The ocean holds vast potential as a renewable energy source, but harnessing its power has been challenging due to low-frequency and high-amplitude stimulation. However, hybrid nanogenerators (HNGs) offer a promising solution to convert ocean energy into usable power efficiently. With their high sensitivity and flexible design, HNGs are ideal for low-frequency environments and remote ocean regions. Combining triboelectric nanogenerators (TENGs) with piezoelectric nanogenerators (PENGs) and electromagnetic nanogenerators (EMGs) creates a unique hybrid system that maximizes energy harvesting. Ultimately, hybrid energy-harvesting systems offer a sustainable and reliable solution for growing energy needs. This study provides an in-depth review of the latest research on ocean energy harvesting by hybrid systems, focusing on self-powered applications. The article also discusses primary hybrid designs for devices, powering self-powered units such as wireless communication systems, climate monitoring systems, and buoys as applications. The potential of HNGs is enormous, and with rapid advancements in research and fabrication, these systems are poised to revolutionize ocean energy harvesting. It outlines the pros and cons of HNGs and highlights the major challenges that must be overcome. Finally, future outlooks for hybrid energy harvesters are also discussed.

Wearable Triboelectric Nanogenerator from Waste Materials for Autonomous Information Transmission via Morse Code.

Electronic waste produced by plastic, toxic, and semiconducting components of existing electronic devices is dramatically increasing environmental pollution. To overcome these issues, the use of eco-friendly materials for designing such devices is attaining much attention. This current work presents a recycled material-based triboelectric nanogenerator (TENG) made of plastic waste and carbon-coated paper wipes (C@PWs), in which the PWs are also collected from a waste bin. The resultant C@PW-based TENG is then used for powering low-power electronic devices and, later, to generate a Morse code from a wearable for autonomous communication. In this application, the end users decode the Morse code from a customized LabVIEW program and read the transmitted signal. With further redesigning, a 9-segment keyboard is developed using nine-TENGs, connected to an Arduino controller to display the 9-segment actuation on a computer screen. Based on the above analysis, our C@PW-TENG device is expected to have an impact on future self-powered sensors and internet of things systems.

Biodegradable metal-organic framework MIL-88A for triboelectric nanogenerator.

Metal-organic frameworks (MOFs) are multifunctional materials with a unique advantage of high porosity and surface area and size tunability and can be modified without altering the topology. The interesting and desirable properties of MOFs led to their exploration for the triboelectric nanogenerator. Herein, a biodegradable MOF MIL-88A for TENG (MIL-TENG) is reported. MIL-88A can be easily synthesized by coordinating iron chloride and fumaric acid in water, thus offering eco-friendly synthesis. Various materials are selected as opposite layers to MIL-88A to analyze triboelectric behavior and performance. The MIL-TENG exhibits an output trend of TENGEC < TENGKapton < TENGFEP. The MIL-88A and FEP generated an output voltage of 80 V and an output current of 2.2 µA. The surface potential measurement and electrical output trend suggest the positive triboelectric behavior of MIL-88A concerning FEP and Kapton. The utilization of biomechanical motions and numerous low-rating electronics powered via a capacitor are demonstrated.

A highly reliable, impervious and sustainable triboelectric nanogenerator as a zero-power consuming active pressure sensor.

The triboelectric effect is one of the most trending effects in energy harvesting technologies, which use one of the most common effects in daily life. Herein, an impervious silicone elastomer-based triboelectric nanogenerator (SE-TENG) is reported with a micro roughness-created silicone elastomer film and Ni foam as triboelectric layers with opposite surface charges. The surface roughness modification process was performed via a cost-effective soft lithography technique using sandpaper. The replicated film was then used as the negative triboelectric layer and porous Ni foam was used as the positive triboelectric layer. The device exhibited the advantage of high stability due to the porous nature of the Ni foam, which could not damage the roughness pattern of the elastomer film. The device generated a maximum electrical output of ∼370 V/6.1 µA with a maximum area power density of ∼17 mW m-2 at a load resistance of 1 GΩ. Furthermore, the SE-TENG device was packed using polyethylene to protect it from humidity and made to be a water-resistant SE-TENG (WR-SE-TENG). The device was stable under different percentages of relative humidity, showing a uniform electrical output in the range of 10% RH to 99% RH. This proves that the packing is highly resistant against moisture and humidity. The device was also used for demonstrating its capability in powering small electronic components such as charging commercial capacitors, glowing LEDs and powering wrist watches. Further, the WR-SE-TENG device was used to scavenge bio-mechanical energy from human motions and also used for a real-time application of zero power consuming/self-powered pressure sensors. As an active sensor, the device showed linear sensing behavior and a sensitivity of 0.492 µA kPa-1.

Biocompatible Collagen Nanofibrils: An Approach for Sustainable Energy Harvesting and Battery-Free Humidity Sensor Applications.

In contrast with the conventional ceramic/oxide humidity sensors (HSs), a self-powered piezoelectric biopolymer HS with reasonable sensitivity, reliability, and a nontoxic and eco-friendly nature is highly desirable. A piezoelectric nanogenerator (PNG)-driven biopolymer-based HS provides a pathway toward a sustainable and greener environment in the field of smart sensors. For that, a piezoelectric collagen nanofibril biopolymer coated on to a cotton fabric has dual functionality (energy harvesting and sensor). Collagen PNG generates a maximum of 45 V/250 nA upon 5 N and can also work as a sensor to measure various percentages of relative humidity (% RH). The HS shows a linear response with a good sensitivity (0.1287 µA/% RH) in the range of 50-90% RH. These results open a field of eco-friendly multifunctional nanomaterials toward the development of noninvasive, implantable smart bio-medical systems.

Correction: Adaptable piezoelectric hemispherical composite strips using a scalable groove technique for a self-powered muscle monitoring system.

Correction for 'Adaptable piezoelectric hemispherical composite strips using a scalable groove technique for a self-powered muscle monitoring system' by Nagamalleswara Rao Alluri et al., Nanoscale, 2018, 10, 907-913.

Regulation of Charge Carrier Dynamics in ZnO Microarchitecture-Based UV/Visible Photodetector via Photonic-Strain Induced Effects.

A feasible, morphological influence on photoresponse behavior of ZnO microarchitectures such as microwire (MW), coral-like microstrip (CMS), fibril-like clustered microwire (F-MW) grown by one-step carrier gas/metal catalyst "free" vapor transport technique is reported. Among them, ZnO F-MW exhibits higher photocurrent (IPh ) response, i.e., IPh/ZnO F-MW > IPh/ZnO CMS > IPh/ZnO MW . The unique structural alignment of ZnO F-MW has enhanced the IPh from 14.2 to 186, 221, 290 µA upon various light intensities such as 0 to 6, 11, 17 mW cm-2 at λ405 nm . Herein, the nature of the as-fabricated ZnO photodetector (PD) is also demonstrated modulated by tuning the inner crystals piezoelectric potential through the piezo-phototronic effect. The IPh response of PD decreases monotonically by introducing compressive strain along the length of the device, which is due to the synergistic effect between the induced piezoelectric polarization and photogenerated charge carriers across the metal-semiconductor interface. The current behavior observed at the two interfaces acting as the source (S) and drain (D) is carefully investigated by analyzing the Schottky barrier heights (ΦSB ). This work can pave the way for the development of geometrically modified strain induced performances of PD to promote next generation self-powered optoelectronic integrated devices and switches.

Adaptable piezoelectric hemispherical composite strips using a scalable groove technique for a self-powered muscle monitoring system.

Contrary to traditional planar flexible piezoelectric nanogenerators (PNGs), highly adaptable hemispherical shape-flexible piezoelectric composite strip (HS-FPCS) based PNGs are required to harness/measure non-linear surface motions. Therefore, a feasible, cost-effective and less-time consuming groove technique was developed to fabricate adaptable HS-FPCSs with multiple lengths. A single HS-CSPNG generates 130 V/0.8 µA and can also work as a self-powered muscle monitoring system (SP-MMS) to measure maximum human body part movements, i.e., spinal cord, throat, jaw, elbow, knee, foot stress, palm hand/finger force and inhale/exhale breath conditions at a time or at variable time intervals.

A flexible, planar energy harvesting device for scavenging road side waste mechanical energy via the synergistic piezoelectric response of K0.5Na0.5NbO3-BaTiO3/PVDF composite films.

Flexible, planar composite piezoelectric nanogenerators (C-PNGs) were developed to harness waste mechanical energy using cost-effective composite films (CFs) prepared via a probe-sonication technique. CFs, made up of highly crystalline, randomly oriented lead free piezoelectric nanoparticles (1 - x)K0.5Na0.5NbO3-xBaTiO3, where x = 0.02, 0.04, 0.06, or 0.08 [designated as KNN-xBTO], were impregnated in a polyvinylidene fluoride (PVDF) matrix. The KNN piezoelectric properties were tuned via the substitution of BTO nanoparticles, without altering the orthorhombic phase. A C-PNG device (x ≈ 0.02) generates a maximum open circuit voltage ≈160 V, and the instantaneous area power density is ≈14 mW m-2 upon a low mechanical force ≈0.4 N. The effects of BTO concentration in the KNN lattice, electrical poling effects, the fixed weight ratio of nanoparticles in the PVDF matrix, switching polarity tests, and load resistance analysis of C-PNG devices were investigated with constant mechanical force. Furthermore, the experimentally demonstrated C-PNG device output is sufficient to drive commercial blue light emitting diodes. The C-PNG device was placed on a road side, and the maximum energy generation and stability under real time harsh conditions, such as vehicle motion (motorcycle and bicycle) and human walking, were tested. C-PNG generates a peak-to-peak output voltage ≈16 V, when motorcycle forward/backward motion acts on it. This result indicates that the C-PNG device is a potential candidate to power road side sensors, speed tachometers, light indicators, etc. on highways.