Hierarchical Nanostructured WO₃ with Biomimetic Proton Channels and Mixed Ionic-Electronic Conductivity for Electrochemical Energy Storage

Abstract

Protein channels in biologic systems can effectively transport ions such as proton (H(+)), sodium (Na(+)), and calcium (Ca(+)) ions. However, none of such channels is able to conduct electrons. Inspired by the biologic proton channels, we report a novel hierarchical nanostructured hydrous hexagonal WO3 (h-WO3) which can conduct both protons and electrons. This mixed protonic-electronic conductor (MPEC) can be synthesized by a facile single-step hydrothermal reaction at low temperature, which results in a three-dimensional nanostructure self-assembled from h-WO3 nanorods. Such a unique h-WO3 contains biomimetic proton channels where single-file water chains embedded within the electron-conducting matrix, which is critical for fast electrokinetics. The mixed conductivities, high redox capacitance, and structural robustness afford the h-WO3 with unprecedented electrochemical performance, including high capacitance, fast charge/discharge capability, and very long cycling life (>50,000 cycles without capacitance decay), thus providing a new platform for a broad range of applications.

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

“…These rod structures, which are the result of the preferential growth of the h-WO 3 crystals induced by the capping agent, will benefit proton insertion, and the different directions of these rods may offer more pathways for protons to enter from the electrolyte. [5,54,55,[59][60][61] The TEM image (Figure 1c) confirms the cake-like assembled structure of the fabricated h-WO 3 . The different contrasts revealed in Figure 1c prove that the structures comprise h-WO 3 nanorods with different orientations.…”

“…This is because, first, WO 3 has two distinctive characteristics, namely electrochromism [21,22,47,48] and photochromism, [49][50][51][52][53] arising from the formation of tungsten bronze by reaction with cations such as H + , Na + , and Li + , which simultaneously stores energy. Second, charging and discharging WO 3 , a negative electrode material for supercapacitors, [5,21,22,54,55] needs a negative bias, which may promote reactions with small cations in photoelectrochemical systems. Moreover, as a semiconductor with a narrow bandgap of 2.6-2.8 eV, WO 3 can absorb visible light to generate electron-hole pairs.…”

“…[28,56] Furthermore, h-WO 3 has plenty of large hexagonal tunnels to accommodate small cations coming from the electrolyte, which can neutralize and trap photoexcited electrons. [5,49,54,55] …”

Modulating memristive performance of hexagonal WO3 nanowire by water-oxidized hydrogen ion implantation

“…It is the intriguing crystalline structures and electronic band structures of WO 3 that endow it with outstanding physical properties and potential applications23242526272829. The higher atomic ratio of oxygen to tungsten leaves more empty interstices in the oxygen sub-lattice, and then WO 3 can behave as a solid solvent towards accommodation of external species into its solid framework to form stable intercalation compounds, which endows WO 3 with outstanding electronic and chromic properties.…”

Photoresponsive Smart Coloration Electrochromic Supercapacitor

“…First, conventional electrochromic devices rely on an external power source, and thus makes it unsuitable for any portable, wearable electronics applications. [18,19] In addition, the use of a cellulose-fiber-based substrate can solve the problem associated with flexibility while also having the required transparency Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. [8][9][10][11] In addition, the high electrical resistance of current collectors in electrochromic devices, which causes deceleration of coloration by slowing down the electrons to cause delays in electrochromic-colorswitch time, and the lack of transparency in the conventional current-collector materials are also problematic.…”