Triggering superior sodium ion adsorption on (2 0 0) facet of mesoporous WO3 nanosheet arrays for enhanced supercapacitance

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 345; pp. 165 - 173
• Main Authors: Yin, Zhuocheng, Bu, Yuyu, Ren, Jun, Chen, Shuai, Zhao, Daming, Zou, Yihui, Shen, Shaohua, Yang, Dongjiang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2018
• Subjects: Exposed facet; Flexible asymmetric supercapacitor; Mesoporous WO3 nanosheets; Sodium ion adsorption; Sodium ion adsorption; Mesoporous WO3 nanosheets; Exposed facet; Flexible asymmetric supercapacitor
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2018.03.100

Mesoporous WO3 nanosheets with exposed (2 0 0) facets were anchored on activated carbon cloth (WO3@ACC) via a simple alcohol-thermal process. The exposed (2 0 0) facets triggered superior Na+ adsorption and thus greatly improved pseudocapacitance was achieved over WO3@ACC electrodes, which exceeded most of the previous values reported for WO3 in the Na2SO4 neutral aqueous electrolyte. [Display omitted] •Mesoporous WO3 nanosheets with exposed (2 0 0) facets were anchored on carbon cloth.•The superior Na+ adsorption on (2 0 0) facet of WO3 nanosheets was evidenced by DFT.•The WO3@ACC electrode exhibits a very high and stable specific areal capacitance.•A flexible supercapacitor was fabricated with high energy and power density. Tungsten trioxide (WO3) is believed to be a promising electrode candidate for supercapacitors, due to its reversible surface redox reaction resulted from the almost same W-O bond lengths with different oxidation states. However, the specific capacitance of WO3 electrode is very low (<250 mF cm−2) because of its low conductivity and slow surface redox reaction kinetics. Herein, to address these issues, mesoporous WO3 nanosheets with exposed (2 0 0) facets were anchored on activated carbon cloth (ACC) via a simple two-step process including heat treatment and alcohol-thermal process. The ACC was coated on WO3 seeds and proceed a heat treatment at 500 °C and the time of alcohol-thermal process were 7 h, 8 h, and 9 h labeled as WO3@ACC-n (n = 7, 8, 9). SEM and TEM images confirmed the WO3 nanosheets were successful anchored on the ACC. The WO3@ACC-8 electrode showed the best specific areal capacitance which could reach as high as 659 mF cm−2 at a current density of 5 mA cm−2 and superior stability with almost no decrease in 10,000 cycles in the presence of Na2SO4 as the neutral electrolyte. The capacitance is encouragingly much higher than the previously reported values in a three-electrode system in the neutral aqueous condition. DFT calculations reveal that, in comparison to the (0 0 2) and (0 2 0) facets, the exposed (2 0 0) facets of the mesoporous WO3 nanosheets triggers the superior Na+ adsorption, which accelerates the Na+-involved surface redox reaction for the boosted supercapacitor performance. A flexible asymmetric supercapacitor (FASC) was fabricated from the WO3@ACC electrode, which exhibits high energy density (0.5 mWh cm−3) and power density (62 mW cm−3) without any attenuation during ±180° wide-angle bending.