Stimulus of Work Function on Electron Transfer Process of Intermetallic Nickel-Antimonide Toward Bifunctional Electrocatalyst for Overall Water Splitting.

Engineering the intermetallic nanostructures as an effective bifunctional electrocatalyst for hydrogen and oxygen evolution reactions (HER and OER) is of great interest in green hydrogen production. However, a few non-noble metals act as bifunctional electrocatalysts, exhibiting terrific HER and OER processes reported to date. Herein the intermetallic nickel-antimonide (Ni─Sb) dendritic nanostructure via cost-effective electro-co-deposition method is designed and their bifunctional electrocatalytic property toward HER and OER is unrevealed. The designed Ni─Sb delivers a superior bifunctional activity in 1 m KOH electrolyte, with a shallow overpotential of ≈119 mV at -10 mA for HER and ≈200 mV at 50 mA for OER. The mechanism behind the excellent bifunctional property of Ni─Sb is discussed via "interfacial descriptor" with the aid of Kelvin probe force microscopy (KPFM). This study reveals the rate of electrocatalytic reaction depends on the energy required for electron and proton transfer from the catalyst's surface. It is noteworthy that the assembled Ni─Sb-90 electrolyzer requires only a minuscule cell voltage of ≈1.46 V for water splitting, which is far superior to the art of commercial catalysts.

Decoupling Contact and Rotary Triboelectrification vs Materials Property: Toward Understanding the Origin of Direct-Current Generation in TENG.

Direct-current (DC) triboelectric nanogenerators (TENGs) are increasingly recognized as next-generation power sources for widespread applications. Research has recently focused on developing novel materials as active layers for DC TENGs and device configurations to elucidate the working mechanisms. In this work, we report the use of a carbyne (dehydrohalogenated poly(vinylidene fluoride) (PVDF)) film as a positive-type friction layer for DC TENGs for efficient harvesting of rotary energy. The fabricated carbyne-based rotary TENG generates an output voltage (120 V) with excellent mechanical stability and peak power density (500 µW m-2). The mechanism of DC output generation from the carbyne-based rotary TENG is explained based on halogen removal from PVDF and the electrostatic breakdown effect. Additionally, the humidity effects on the fabricated carbyne-based rotary TENG toward a self-powered humidity sensor are studied in detail with the aid of in situ Raman analysis, Fourier transform infrared spectroscopy, and open-circuit potential measurements. Together, our experimental results demonstrate that using carbyne as an active triboelectric layer for DC TENGs would greatly benefit the next generation of power devices.

Electrospun Polymer-Derived Carbyne Supercapacitor for Alternating Current Line Filtering.

The filtering device is a vital component of electronic goods that rectifies ripples which occur upon converting alternating current (AC) to direct current (DC) and attenuates high-frequency noise during switching or voltage declines. Classical filtering devices suffer from low performance metrics and are bulky, limiting their use in modern electronic devices. The fabrication process of electrode materials for high-frequency symmetric supercapacitor (HFSSC) is complicated, hindering commercialization. Herein, for the first time, the design of a high-performance stand-alone carbyne film comprised of sp/sp2 -hybridized carbon as an electrode for AC filtering under a wide frequency range is reported. The carbyne film as HFSSC shows the ideal capacitive behavior at ultrahigh scan rate of 10 000 V s-1 with excellent linearity which is top among the reported AC line filter capacitor. The carbyne HFSSC exhibits a high energy density of 703.25 µF V2  cm-2 at 120 Hz, which is superior to that of current commercial electrolytic filters and many reported AC line supercapacitors. As a proof of concept, a carbyne device is implemented in a real time AC to DC adaptor that demonstrates excellent filtering performance at high frequencies.

Topochemically synthesized MoS2 nanosheets: A high performance electrode for wide-temperature tolerant aqueous supercapacitors.

This work describes the formation of two-dimensional molybdenum di-sulfide (MoS2) nanosheets via topochemical sulfurization of MoO3 microplates and its applications towards wide-temperature tolerant supercapacitors. Physico-chemical characterizations such as XRD, FE-SEM, HR-TEM, XPS and elemental mapping analysis revealed the formation of MoS2 nanosheets with lateral size in the range of 200 nm. The electrochemical properties of the MoS2 electrode using three-electrode configuration tests revealed the presence of pseudocapacitive mechanism of charge-storage with a high capacitance (119.38 F g-1) from cyclic voltammetry profiles and superior cyclic stability of 95.1% over 2000 cycles. The symmetric supercapacitor (SSC) fabricated using MoS2 electrodes delivered a high-energy density (6.56 Wh kg-1) and high-power density (2500 W kg-1) with long cycle life. The electrochemical performance of the MoS2 SSC exhibited ~121% improvement at 80 °C compared to that achieved at 20 °C and the mechanism of improved properties were examined with the use of electrochemical impedance spectroscopy. These experimental results indicate usefulness of topochemically synthesized MoS2 for construction of wide-temperature tolerant supercapacitors that can be useful in a variety of industrial sectors.

Probing the energy conversion process in piezoelectric-driven electrochemical self-charging supercapacitor power cell using piezoelectrochemical spectroscopy.

The design and development of self-charging supercapacitor power cells are rapidly gaining interest due to their ability to convert and store energy in an integrated device. Here, we have demonstrated the fabrication of a self-charging supercapacitor using siloxene sheets as electrodes and siloxene-based polymeric piezofiber separator immobilized with an ionogel electrolyte. The self-charging properties of the fabricated device subjected to various levels of compressive forces showed their ability to self-charge up to a maximum of 207 mV. The mechanism of self-charging process in the fabricated device is discussed via "piezoelectrochemical effect" with the aid of piezoelectrochemical spectroscopy measurements. These studies revealed the direct evidence of the piezoelectrochemical phenomenon involved in the energy conversion and storage process in the fabricated device. This study can provide insight towards understanding the energy conversion process in self-charging supercapacitors, which is of significance considering the state of the art of piezoelectric driven self-charging supercapacitors.

Free-Standing PVDF/Reduced Graphene Oxide Film for All-Solid-State Flexible Supercapacitors towards Self-Powered Systems.

The development of polymer-based devices has attracted much attention due to their miniaturization, flexibility, lightweight and sustainable power sources with high efficiency in the field of wearable/portable electronics, and energy system. In this work, we proposed a polyvinylidene fluoride (PVDF)-based composite matrix for both energy harvesting and energy storage applications. The physicochemical characterizations, such as X-ray diffraction, laser Raman, and field-emission scanning electron microscopy (FE-SEM) analyses, were performed for the electrospun PVDF/sodium niobate and PVDF/reduced graphene oxide composite film. The electrospun PVDF/sodium niobate nanofibrous mat has been utilized for the energy harvester which shows an open circuit voltage of 40 V (peak to peak) at an applied compressive force of 40 N. The PVDF/reduced graphene oxide composite film acts as the electrode for the symmetric supercapacitor (SSC) device fabrication and investigated for their supercapacitive properties. Finally, the self-charging system has been assembled using PVDF/sodium niobate (energy harvester), and PVDF/reduced graphene oxide SSC (energy storage) and the self-charging capability is investigated. The proposed self-charging system can create a pathway for the all-polymer based composite high-performance self-charging system.

Carbyne-enriched carbon anchored on nickel foam: A novel binder-free electrode for supercapacitor application.

Carbon- and carbon derivatives are widely employed as efficient electrode materials for supercapacitor applications. Herein, we demonstrate a cost-effective dip-coating process followed by dehydrohalogenation of PVDF-Ni for the preparation of carbyne enriched carbon anchored on nickel (CEC-Ni) as high-performance electrode material. The removal of halogens in the prepared CEC-Ni were widely characterized using XRD, XPS, Laser Raman, and FT-IR analysis. The occurrence of carbon-carbon vibration in the prepared CEC-Ni foam was confirmed using FT-IR spectroscopy. Laser Raman analysis confirms that the CEC-Ni foam contains both sp and sp2 hybridized carbon. The electrochemical properties of prepared carbyne enriched carbon anchored on nickel foam electrode (CEC-NiE) showed an ideal capacitive properties and delivered a maximum specific capacitance of about 106.12 F g-1 with excellent cyclic retention. Furthermore, the mechanism of charge-storage in the CEC-NiE was analyzed using Dunn's method. In additon, the asymmetric supercapacitor device was fabricated using CEC-NiE as positive and rGO as negative electrode achieved a remarkable energy density of 33.57 Wh Kg-1 with a maximal power density of 14825.71 W Kg-1. These results suggested that the facile preparation of CEC-NiE could be a promising and effective electrode material for future energy storage application.

Blue TiO2 nanosheets as a high-performance electrode material for supercapacitors.

We are reporting the use of blue titanium oxide (b-TiO2) nanostructures as advanced electrode material for high performance supercapacitor for the first time. A one-pot hydrothermal route was employed for the oxidation of layered titanium diboride (TiB2) into b-TiO2 nanosheets. The b-TiO2 nanosheets are prepared via hydrothermal oxidation of TiB2. Physico-chemical characterizations such as X-ray diffraction, UV-visible, photoluminescence spectroscopy, electron spin resonance spectroscopy, laser Raman spectrum, X-ray photoelectron spectroscopy, and morphological studies revealed the formation of sheet-like b-TiO2 nanostructures. The energy storage properties of the b-TiO2 electrode were examined using aqueous and organic electrolytes. The cyclic voltammetry and charge-discharge analysis of b-TiO2 electrode using 1 M Na2SO4 revealed their pseudocapacitive nature with a high specific capacitance (∼19 mF cm-2). The b-TiO2 based symmetric supercapacitor (SSC) device using organic liquid (1 M TEABF4) works over a wide operating potential window (3 V) and delivered a high specific capacitance (6.67 F g-1 or 3.58 mF cm-2), possess high energy density and power density with excellent cyclic stability over 10,000 cycles. Collectively, these studies demonstrated the usefulness of b-TiO2 as a novel electrode material for high performance supercapacitor.

Understanding the Thermal Treatment Effect of Two-Dimensional Siloxene Sheets and the Origin of Superior Electrochemical Energy Storage Performances.

Two-dimensional siloxene sheets are an emerging class of materials with an eclectic range of potential applications including electrochemical energy conversion and storage sectors. Here, we demonstrated the dehydrogenation/dehydroxylation of siloxene sheets by thermal annealing at high temperature (HT) and investigated their supercapacitive performances using ionic liquid electrolyte. The X-ray diffraction analysis, spectroscopic (Fourier transform infrared, laser Raman, and X-ray photoelectron spectroscopy) studies, and morphological analysis of HT-siloxene revealed the removal of functional groups at the edges/basal planes of siloxene, and preservation of oxygen-interconnected Si6 rings with sheet-like structures. The HT-siloxene symmetric supercapacitor (SSC) operates over a wide potential window (0-3.0 V), delivers a high specific capacitance (3.45 mF cm-2), high energy density of about 15.53 mJ cm-2 (almost 2-fold higher than that of the as-prepared siloxene SSC), and low equivalent series resistance (compared to reported silicon-based SSCs) with excellent rate capability and long cycle life over 10 000 cycles.