Quantitative Analysis of Charge Storage Process of Tungsten Oxide that Combines Pseudocapacitive and Electrochromic Properties

Abstract

Tungsten oxide has been recently demonstrated interesting and promising bifunctionalities that combine electrochromism and pseudocapacitance. However, understanding about the charge storage process of pseudocapacitive tungsten oxide film is very limited. Our quantitative investigation clearly reveals that the capacity performance of tungsten oxide film is thickness-dependent. In particular, the 100 nm-thick tungsten oxide film exhibits highest charge capacity density at high rates, with nearly 242.1 C g −1 stored reversibly in 6 s. The 100 nmthick tungsten oxide film stores charges mainly by capacitive effects (including both electric double layer capacitance and pseudocapacitance). For example, at a scan rate of 5 mV s −1 , more than 78% stored charges is attributed to capacitive effects, according to the cyclic voltammetry analysis. Furthermore, pseudocapacitance is responsible for around 70% of the capacitive charge storage based on the electrochemical impedance spectroscopy analysis. The contributions of diffusion-controlled process, electric double layer capacitive process, and pseudocapacitive process have been discussed in detailed and successfully identified. Overall, this work provides insight into the charge storage process of tungsten oxide, and our new findings can shed light on other transition metal oxide-based electrochemical energy storage systems.

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.…”

“…It is obvious that all b values at potentials below 0 V are smaller than 1 because of the insertion of protons into the h-WO 3 crystal due to the limitation of diffusion or intrinsic ohmic contributions at high scan rates. [5,[70][71][72] To be more specific, during the cathodic process (Figure 4c), the b values, under illumination and in the dark, decrease from ≈1 to ≈0.6 with decreasing potential, which means that protons may encounter more obstructions during insertion at lower potentials. This may stem from the deeper insertion of protons into h-WO 3 .…”

“…In particular, a b value of 0.5 means the process is slow diffusion dominated, and a b value of 1 represents a fast surface capacitive process. [5,[70][71][72] It is shown in Figure S7 (Supporting Information) that the b values of the cathodic and anodic peaks are all near 1, in the dark and under illumination. This reveals the suitability of h-WO 3 as the active material for supercapacitors.…”

On the Supercapacitive Behaviour of Anodic Porous WO3-Based Negative Electrodes

“…This enhancement results from the additive effect of fast superficial redox reactions and electric double layer formation at the electrode/electrolyte interface. [12,[16][17][18][19][20][21][22][23] show promising pseudocapacitive behaviour as well as reasonable capacity retention in asymmetric systems in the negative potential region.…”

Electrochromic energy storage devices

“…What's more, a large scale pseudocapacitive WO 3 -based glass window (15 cm  15 cm) was fabricated as a prototype. Thereafter, they quantitatively investigated the charge storage process of tungsten oxide film [51]. It is noteworthy that WO 3 film usually suffers from iontrapping-induced degradation of optical modulation and cycle reversibility on prolonged cation ion exchange, and this effect can be successfully eliminated by constant-current-driven detrapping, providing a general framework for developing and designing superior electrochromic devices [52].…”