Block-Copolymer-Assisted One-Pot Synthesis of Ordered Mesoporous WO3−x/Carbon Nanocomposites as High-Rate-Performance Electrodes for Pseudocapacitors

Abstract

An ordered mesoporous tungsten-oxide/carbon (denoted as m-WO3-x-C-s) nanocomposite is synthesized using a simple one-pot method using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as a structure-directing agent. The hydrophilic PEO block interacts with the carbon and tungsten precursors (resol polymer and WCl6), and the PS block is converted to pores after heating at 700 degrees C under a nitrogen flow. The m-WO3-x-C-s nanocomposite has a high Brunauer-Emmett-Teller (BET) surface area and hexagonally ordered pores. Because of its mesoporous structure and high intrinsic density of tungsten oxide, this material exhibits a high average volumetric capacitance and gravimetric capacitance as a pseudocapacitor electrode. In comparison with reduced mesoporous tungsten oxide (denoted as m-WO3-x-h), which is synthesized by a tedious hard template approach and further reduction in a H-2/N-2 atmosphere, m-WO3-x-C-s shows a high capacitance and enhanced rate performance, as confirmed by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The good performance of m-WO3-x-C-s is attributed to the high surface area arising from the mesoporous structure, the large interconnected mesopores, and the low internal resistance from the well-dispersed reduced tungsten oxide and amorphous carbon composite structure. Here, the amorphous carbon acts as an electrical pathway for effective pseudocapacitor behavior of WO3-x.