Boosting areal capacitance in WO₃-based supercapacitor materials by stacking nanoporous composite films

High-capacity energy storage devices are of interest in various applications, but are not always easy to scale up, and they may experience tradeoffs between areal and gravimetric capacitance. Here, nanoporous WO₃/MoO₃ films are prepared using electroexploding wire and spray-coating techniques for the exploration of the tradeoffs between areal and gravimetric capacitance. The nanoporous films are extended through nanoparticle stacking, which is accompanied by increasing thickness. The diffusion coefficient measured with cyclic voltammetry increases exponentially with thickness and reaches 1.12 × 10⁻⁷ cm²/s for Li-ion intercalations. In galvanostatic charge-discharge curves, the highest areal capacitance of 496 mF/cm² is obtained at 0.5 mA/cm² for an 18-μm-thick film, and the gravimetric capacitance is 95.2 F/g at 0.13 A/g for a 1.6-μm-thick film. The film thickness is adjusted to optimize either areal or gravimetric capacitances, and high retention abilities imply the possibility of application in high-performance supercapacitive applications.