Kaushik Parida

Enhanced Piezoelectric Energy Harvesting Performance of Flexible PVDF-TrFE Bilayer Films with Graphene Oxide

Ferroelectric materials have attracted interest in recent years due to their application in energy harvesting owing to its piezoelectric nature. Ferroelectric polymers are flexible and can sustain larger strains compared to inorganic counterparts, making them attractive for harvesting energy from mechanical vibrations. Herein, we report, for the first time, the enhanced piezoelectric energy harvesting performance of the bilayer films of poled poly(vinylidene fluoride-trifluoroethylene) [PVDF-TrFE] and graphene oxide (GO). The bilayer film exhibits superior energy harvesting performance with a voltage output of 4 V and power output of 4.41 μWcm(-2) compared to poled PVDF-TrFE films alone (voltage output of 1.9 V and power output of 1.77 μWcm(-2)). The enhanced voltage and power output in the presence of GO film is due to the combined effect of electrostatic contribution from graphene oxide, residual tensile stress, enhanced Youngs modulus of the bilayer films, and the presence of space charge at the interface of the PVDF-TrFE and GO films, arising from the uncompensated polarization of PVDF-TrFE. Higher Youngs modulus and dielectric constant of GO led to the efficient transfer of mechanical and electrical energy.

Highly Transparent, Stretchable, and Self‐Healing Ionic‐Skin Triboelectric Nanogenerators for Energy Harvesting and Touch Applications

Recently developed triboelectric nanogenerators (TENGs) act as a promising power source for self-powered electronic devices. However, the majority of TENGs are fabricated using metallic electrodes and cannot achieve high stretchability and transparency, simultaneously. Here, slime-based ionic conductors are used as transparent current-collecting layers of TENG, thus significantly enhancing their energy generation, stretchability, transparency, and instilling self-healing characteristics. This is the first demonstration of using an ionic conductor as the current collector in a mechanical energy harvester. The resulting ionic-skin TENG (IS-TENG) has a transparency of 92% transmittance, and its energy-harvesting performance is 12 times higher than that of the silver-based electronic current collectors. In addition, they are capable of enduring a uniaxial strain up to 700%, giving the highest performance compared to all other transparent and stretchable mechanical-energy harvesters. Additionally, this is the first demonstration of an autonomously self-healing TENG that can recover its performance even after 300 times of complete bifurcation. The IS-TENG represents the first prototype of a highly deformable and transparent power source that is able to autonomously self-heal quickly and repeatedly at room temperature, and thus can be used as a power supply for digital watches, touch sensors, artificial intelligence, and biointegrated electronics.

Self-powered pressure sensor for ultra-wide range pressure detection

The next generation of sensors should be self-powered, maintenance-free, precise, and have wide-ranging sensing abilities. Despite extensive research and development in the field of pressure sensors, the sensitivity of most pressure sensors declines significantly at higher pressures, such that they are not able to detect a wide range of pressures with a uniformly high sensitivity. In this work, we demonstrate a single-electrode triboelectric pressure sensor, which can detect a wide range of pressures from 0.05 to 600 kPa with a high degree of sensitivity across the entire range by utilizing the synergistic effects of the piezoelectric polarization and triboelectric surface charges of self-polarized polyvinyldifluoride-trifluoroethylene (P(VDF-TrFE)) sponge. Taking into account both this wide pressure range and the sensitivity, this device exhibits the best performance relative to that of previously reported self-powered pressure sensors. This achievement facilitates wide-range pressure detection for a broad spectrum of applications, ranging from simple human touch, sensor networks, smart robotics, and sports applications, thus paving the way forward for the realization of next-generation sensing devices. Moreover, this work addresses the critical issue of saturation pressure in triboelectric nanogenerators and provides insights into the role of the surface charge on a piezoelectric polymer when used in a triboelectric nanogenerator.

Design of Mixed-Metal Silver Decamolybdate Nanostructures for High Specific Energies at High Power Density.

Mixed-metal molybdates are interesting host materials for ion-insertion electrodes due to their versatile crystal chemistry, which confers a highway for the conduction of electrons as well as ions. Silver decamolybdate in triclinic crystal structure (T-Ag6 Mo10 O33 ) consists of layers of MoO6 octahedra separated by arrays of silver ions that are able to store a high amount of charges.

A Stretchable and Transparent Nanocomposite Nanogenerator for Self-Powered Physiological Monitoring

Smart sensing electronic devices with good transparency, high stretchability, and self-powered sensing characteristics are essential in wearable health monitoring systems. This paper innovatively proposes a stretchable nanocomposite nanogenerator with good transparency that can be conformally attached to the human body to harvest biomechanical energy and monitor physiological signals. The work reports an innovative device that uses sprayed silver nanowires as transparent electrodes and sandwiches a nanocomposite of piezoelectric BaTiO3 and polydimethylsiloxane as the sensing layer, which exhibits good transparency and mechanical transformability with stretchable, foldable, and twistable properties. The highly flexible nanogenerator affords a good input-output linearity under the vertical force and the sensing ability to detect lateral stretching deformation up to 60% strain under piezoelectric mechanisms. Furthermore, the proposed device can effectively harvest touch energies from the human body as a single-electrode triboelectric nanogenerator. Under periodic contact and separation, a maximum output voltage of 105 V, a current density of 6.5 μA/cm2, and a power density of 102 μW/cm2 can be achieved, exhibiting a good power generation performance. Owing to the high conformability and excellent sensitivity of the nanogenerator, it can also act as a self-powered wearable sensor attached to different parts of the human body for real-time monitoring of the human physiological signals such as eye blinking, pronunciation, arm movement, and radial artery pulse. The designed nanocomposite nanogenerator shows great potential for use in self-powered e-skins and healthcare monitoring systems.

Localized Charge Transfer in Two-Dimensional Molybdenum Trioxide

Molybdenum trioxide is an interesting inorganic system in which the empty 4d states have potential to hold extra electrons and therefore can change states from insulating opaque (MoO3) to colored semimetallic (HxMoO3). Here, we characterize the local electrogeneration and charge transfer of the synthetic layered two-dimensional 2D MoO3-II (a polymorph of MoO3 and analogous to α-MoO3) in response to two different redox couples, i.e., [Ru(NH3)6]3+ and [Fe(CN)6]3- by scanning electrochemical microscopy (SECM). We identify the reduction of [Ru(NH3)6]3+ to [Ru(NH3)6]2+ at the microelectrode that leads to the reduction of MoO3-II to conducting blue-colored molybdenum bronze HxMoO3. It is recognized that the dominant conduction of the charges occurred preferentially at the edges active sites of the sheets, as edges of the sheets are found to be more conducting. This yields positive feedback current when approaching the microelectrode toward 2D MoO3-II-coated electrode. In contrast, the [Fe(CN)6]4-, which is reduced from [Fe(CN)6]3-, is found unfavorable to reduce MoO3-II due to its higher redox potential, thus showing a negative feedback current. The charge transfer on MoO3-II is further studied as a function of applied potential. The results shed light on the charge transfer behavior on the surface of MoO3-II coatings and opens the possibility of locally tuning of their oxidation states.

Skin-touch-actuated textile-based triboelectric nanogenerator with black phosphorus for durable biomechanical energy harvesting

Textiles that are capable of harvesting biomechanical energy via triboelectric effects are of interest for self-powered wearable electronics. Fabrication of conformable and durable textiles with high triboelectric outputs remains challenging. Here we propose a washable skin-touch-actuated textile-based triboelectric nanogenerator for harvesting mechanical energy from both voluntary and involuntary body motions. Black phosphorus encapsulated with hydrophobic cellulose oleoyl ester nanoparticles serves as a synergetic electron-trapping coating, rendering a textile nanogenerator with long-term reliability and high triboelectricity regardless of various extreme deformations, severe washing, and extended environmental exposure. Considerably high output (~250–880 V, ~0.48–1.1 µA cm−2) can be attained upon touching by hand with a small force (~5 N) and low frequency (~4 Hz), which can power light-emitting diodes and a digital watch. This conformable all-textile-nanogenerator is incorporable onto cloths/skin to capture the low output of 60 V from subtle involuntary friction with skin, well suited for users’ motion or daily operations.Incorporation of triboelectric nanogenerators into textiles is attractive for self-powered wearable electronics. Here the authors employ black phosphorus with a hydrophobic coating in a durable, washable, and air permeable textile-based device that converts biomechanical motion into electricity.

Synthesis and Characterization of SiNW-MnO2 Core-Shell Structure

A simple and low temperature approach has been used for the deposition of manganese oxide (MnO2) film and nanoparticles on silicon nanowires (SiNWs). Firstly, SiNWs were grown using hot wire chemical vapour process (HWCVP) technique via Vapor-Liquid-Solid (VLS) mechanism using Sn as a catalyst and then electrophoretic deposition method (EPD) was used to deposit MnO2 on them. Since SiNWs have good electron transportation and high aspect ratio, the role of SiNWs is thus for improving the electrical conduction and the surface area for MnO2 for its application in a desired form. First the deposition parameters were optimized on a transparent conductive oxide (TCO) coated glass substrate to control the thickness of the MnO2 film and then it was synthesized on SiNWs. The deposition of MnO2 has been confirmed by FEG-SEM and EDX. This structure of MnO2-SiNWs could be useful for various applications.