Capacitance Enhancement in a Semiconductor Nanostructure‐Based Supercapacitor by Solar Light and a Self‐Powered Supercapacitor–Photodetector System

Abstract

The effects of the environment on the energy storage of supercapacitors as well as the underlying mechanisms have long been neglected. This paper reports that the capacitance of hexagonal‐phase tungsten oxide (h‐WO3)‐based supercapacitors increases by ≈17% under solar light. Thorough analyses of the wavelength dependence of the enhancement, capacitive mechanism, energy storage dynamics, and impedance reveal that: i) photoexcited electrons are responsible for the enhancement; ii) the insertion of protons into the large hexagonal tunnels of h‐WO3, instead of a surface capacitive process, is greatly facilitated by the photoexcited electrons; iii) the theoretical light‐induced capacitance enhancement can reach up to 38% for a h‐WO3‐based supercapacitor. Moreover, as an application of this finding, a self‐powered photodetector based on a h‐WO3 supercapacitor is fabricated, wherein the photoexcited electrons serve as the signal for detecting solar light. The device works without an external power source and can be considered as an ultimately integrated power source–sensor system. This work sheds light on the interaction between solar light and a semiconductor‐based supercapacitor as well as the concrete mechanisms behind the phenomenon. These efforts also open the door to the design of highly integrated, brand‐new power source–sensor systems.

A New Facile Synthesis of Tungsten Oxide from Tungsten Disulfide: Structure Dependent Supercapacitor and Negative Differential Resistance Properties

“…Several studies have demonstrated that the tendency of ion insertion/extraction enhances with increasing the symmetry of crystalline forms, i.e., monoclinic phase < orthorhombic phase < tetragonal phase < cubic phase . Presently, some transition‐metal oxides or conducting polymers are used as active materials for supercapacitors because they all participate in fast Faradic reactions between the active materials and electrolytes . To cope the increasing demand of energy storage, WO 3 is a promising smart material especially as a negative electrode for fabrication of high‐performance electrochemical energy storage devices.…”

“…All the above techniques to make WO 3 nanostructures have significant advantages and disadvantages from the points of controlling the crystal growth for shape and size, processing temperature, impurities, product yield, and homogeneity. In the microwave synthesis generally Na 2 WO 4 .2H 2 O and WCl 6 are used as precursor, which are heated in microwave reactor at 180–200 °C . Fortunato and co‐workers have reported pH dependent growth of WO 3 crystal, using Na 2 WO 4 .2H 2 O as precursor and NaCl as structure‐directing agent (SDA).…”

Metal–Organic Framework Derived Co3O4/TiO2/Si Heterostructured Nanorod Array Photoanodes for Efficient Photoelectrochemical Water Oxidation

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The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10. [12,13] Metal oxides (MOs), such as TiO 2 , [14] α-Fe 2 O 3 , [15] and WO 3 , [16,17] have been widely investigated as the photoanode materials for PEC water splitting, for their low-cost, environmentfriendly properties. photoexcitation of semiconductor photoanode; the separation and migration of photoinduced carriers; the surface water reduction on the cathode; and water oxidation on the photoanode with photoinduced electrons/holes.

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Highly Integrated Supercapacitor‐Sensor Systems via Material and Geometry Design

“…On one hand, from the viewpoint of materials for a wearable integrated device, conducting polymers such as polypyrrole (PPy) are intrinsically flexible and can maintain or even enhance performance under small strains, validating themselves as promising candidates for wearable devices . Like graphene and many metal oxides, PPy is both electrocapacitive and light sensitive, making the integration of energy storage and photodetection in a wearable device possible. In addition, these functions can be effectively combined to realize a self‐powered photodetector by monitoring the changes of a discharging current.…”