Hulin Zhang

Human Skin Based Triboelectric Nanogenerators for Harvesting Biomechanical Energy and as Self- Powered Active Tactile Sensor System

We report human skin based triboelectric nanogenerators (TENG) that can either harvest biomechanical energy or be utilized as a self-powered tactile sensor system for touch pad technology. We constructed a TENG utilizing the contact/separation between an area of human skin and a polydimethylsiloxane (PDMS) film with a surface of micropyramid structures, which was attached to an ITO electrode that was grounded across a loading resistor. The fabricated TENG delivers an open-circuit voltage up to -1000 V, a short-circuit current density of 8 mA/m(2), and a power density of 500 mW/m(2) on a load of 100 MΩ, which can be used to directly drive tens of green light-emitting diodes. The working mechanism of the TENG is based on the charge transfer between the ITO electrode and ground via modulating the separation distance between the tribo-charged skin patch and PDMS film. Furthermore, the TENG has been used in designing an independently addressed matrix for tracking the location and pressure of human touch. The fabricated matrix has demonstrated its self-powered and high-resolution tactile sensing capabilities by recording the output voltage signals as a mapping figure, where the detection sensitivity of the pressure is about 0.29 ± 0.02 V/kPa and each pixel can have a size of 3 mm × 3 mm. The TENGs may have potential applications in human-machine interfacing, micro/nano-electromechanical systems, and touch pad technology.

Single-Electrode-Based Sliding Triboelectric Nanogenerator for Self-Powered Displacement Vector Sensor System

We report a single-electrode-based sliding-mode triboelectric nanogenerator (TENG) that not only can harvest mechanical energy but also is a self-powered displacement vector sensor system for touching pad technology. By utilizing the relative sliding between an electrodeless polytetrafluoroethylene (PTFE) patch with surface-etched nanoparticles and an Al electrode that is grounded, the fabricated TENG can produce an open-circuit voltage up to 1100 V, a short-circuit current density of 6 mA/m(2), and a maximum power density of 350 mW/m(2) on a load of 100 MΩ, which can be used to instantaneously drive 100 green-light-emitting diodes (LEDs). The working mechanism of the TENG is based on the charge transfer between the Al electrode and the ground by modulating the relative sliding distance between the tribo-charged PTFE patch and the Al plate. Grating of linear rows on the Al electrode enables the detection of the sliding speed of the PTFE patch along one direction. Moreover, we demonstrated that 16 Al electrode channels arranged along four directions were used to monitor the displacement (the direction and the location) of the PTFE patch at the center, where the output voltage signals in the 16 channels were recorded in real-time to form a mapping figure. The advantage of this design is that it only requires the bottom Al electrode to be grounded and the top PTFE patch needs no electrical contact, which is beneficial for energy harvesting in automobile rotation mode and touch pad applications.

Triboelectric Nanogenerator for Harvesting Wind Energy and as Self-Powered Wind Vector Sensor System

We report a triboelectric nanogenerator (TENG) that plays dual roles as a sustainable power source by harvesting wind energy and as a self-powered wind vector sensor system for wind speed and direction detection. By utilizing the wind-induced resonance vibration of a fluorinated ethylene-propylene film between two aluminum foils, the integrated TENGs with dimensions of 2.5 cm × 2.5 cm × 22 cm deliver an output voltage up to 100 V, an output current of 1.6 μA, and a corresponding output power of 0.16 mW under an external load of 100 MΩ, which can be used to directly light up tens of commercial light-emitting diodes. Furthermore, a self-powered wind vector sensor system has been developed based on the rationally designed TENGs, which is capable of detecting the wind direction and speed with a sensitivity of 0.09 μA/(m/s). This work greatly expands the applicability of TENGs as power sources for self-sustained electronics and also self-powered sensor systems for ambient wind detection.

Flexible Hybrid Energy Cell for Simultaneously Harvesting Thermal, Mechanical, and Solar Energies

We report the first flexible hybrid energy cell that is capable of simultaneously or individually harvesting thermal, mechanical, and solar energies to power some electronic devices. For having both the pyroelectric and piezoelectric properties, a polarized poly(vinylidene fluoride) (PVDF) film-based nanogenerator (NG) was used to harvest thermal and mechanical energies. Using aligned ZnO nanowire arrays grown on the flexible polyester (PET) substrate, a ZnO-poly(3-hexylthiophene) (P3HT) heterojunction solar cell was designed for harvesting solar energy. By integrating the NGs and the solar cells, a hybrid energy cell was fabricated to simultaneously harvest three different types of energies. With the use of a Li-ion battery as the energy storage, the harvested energy can drive four red light-emitting diodes (LEDs).

A Single‐Electrode Based Triboelectric Nanogenerator as Self‐Powered Tracking System

A newly designed triboelectric nanogenerator (TENG) is demonstrated based on a contact-separation process between an Al foil and a finite size polyamide (PA) film. The working mechanism is based on charge transfer between the Al foil and ground. A 4×4 matrix of TENG array can be used for tracking motion by recording the output voltages signals in real-time to form a pressure map.

Silicon-Based Hybrid Energy Cell for Self-Powered Electrodegradation and Personal Electronics

Silicon (Si)-based solar cell is by far the most established solar cell technology. The surface of a Si solar cell is usually covered by a layer of transparent material to protect the device from corrosion, contamination and mechanical damage. Here, we replaced this protection layer by a thin layer film of polydimethysiloxane nanowires. Based on this layer and using the conductive layer on the surface of the wavy Si, we have fabricated a triboelectric nanogenerator (TENG). The solar cell and the TENG form a hybrid energy cell for simultaneously harvesting solar and mechanical energies. The hybrid energy cell can be directly used for self-powered electrodegradation of rhodamine B, where the degradation percentage is up to 98% in 10 min. Moreover, the produced energy can also be stored in the Li-ion batteries for driving some personal electronics such as a red laser diode and a commercial cell phone.

Hybrid Energy Cell for Degradation of Methyl Orange by Self-Powered Electrocatalytic Oxidation

In general, methyl orange (MO) can be degraded by an electrocatalytic oxidation process driven by a power source due to the generation of superoxidative hydroxyl radical on the anode. Here, we report a hybrid energy cell that is used for a self-powered electrocatalytic process for the degradation of MO without using an external power source. The hybrid energy cell can simultaneously or individually harvest mechanical and thermal energies. The mechanical energy was harvested by the triboelectric nanogenerator (TENG) fabricated at the top by using a flexible polydimethysiloxane (PDMS) nanowire array with diameters of about 200 nm. A pyroelectric nanogenerator (PENG) was fabricated below the TENG to harvest thermal energy. The power output of the device can be directly used for electrodegradation of MO, demonstrating a self-powered electrocatalytic oxidation process.

A hybrid energy cell for self-powered water splitting†

Production of hydrogen (H2) by splitting water using the electrolysis effect is a potential source of clean and renewable energy. However, it usually requires an external power source to drive the oxidation or reduction reactions of H2O molecules, which largely limits the development of this technology. Here, we fabricated a hybrid energy cell that is an integration of a triboelectric nanogenerator, a thermoelectric cell, and a solar cell, which can be used to simultaneously/individually harvest mechanical, thermal, and/or solar energies. The power output of the hybrid energy cell can be directly used for splitting water without an external power source. The volume of the produced H2 has a linear relationship with the splitting time at a production speed of 4 × 10−4 mL s−1. Moreover, the produced energies can also be stored in a Li-ion battery for water splitting as well as other uses.

Simultaneously harvesting mechanical and chemical energies by a hybrid cell for self-powered biosensors and personal electronics

Electrochemical cells (ECs) are devices that convert chemical energy into electricity through spontaneous oxidation–reduction reactions that occur separately at two electrodes through the transport of protons in the electrolyte solution and the flow of electrons in the external circuit. A triboelectric nanogenerator (TENG) is an effective device that converts mechanical energy into electricity using organic/polymer materials by a contact induced electrification process followed by charge separation. In this paper, we demonstrate the first integration of an EC and a TENG for simultaneously harvesting chemical and mechanical energy, and its application for powering a sensor and even personal electronics. An EC was fabricated using a Cu/NaCl solution/Al structure, on which a thin polydimethylsiloxane (PDMS) film with a micropyramid surface structure was used as the protection layer of the EC for anti-corrosion, anti-contamination and anti-mechanical damage. A TENG was fabricated based on a contact-and-separation process between the PDMS protection layer and the Al electrode layer of the EC. The output performance of the TENG can be increased by embedding BaTiO3 nanoparticles into the PDMS film layer to enhance the dielectric property. Moreover, we also demonstrated that the produced hybrid energies can be stored in a Li-ion battery for lighting up 30 green LEDs.

Electret film-enhanced triboelectric nanogenerator matrix for self-powered instantaneous tactile imaging.

We report the first self-powered electronic skin that consists of light-emitting diode (LED) and triboelectric nanogenerator (TENG) arrays that can be utilized for spatially mapping applied instantaneous-touch events and tracking the movement location of the target object by recording the electroluminescent signals of the LEDs without external power sources. The electret film-based TENG can deliver an open-circuit voltage of about -1070 V, a short-circuit current density of 10 mA/m(2), and a power density of 288 mW/m(2) on an external load of 100 MΩ. The LEDs can be turned on locally when the back surface of the active matrix is touched, and the intensity of the emitted light depends on the magnitude of the applied local pressure on the device. A constructed active matrix of the LED-TENG array (8 × 7 pixels) can achieve self-powered, visual, and high-resolution tactile sensing by recording the electroluminescent signals from all of the pixels, where the active size of each pixel can be decreased to 10 mm(2). This work is a significant step forward in self-powered tactile-mapping visualization technology, with a wide range of potential applications in touchpad technology, personal signatures, smart wallpapers, robotics, and safety-monitoring devices.