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

Tungsten trioxide (WO3) is promising electrochromic materials applied to smart windows for the containment of CO2 emission, energy crisis, and climate change. It incidentally manifests itself as potential supercapacitive materials for energy storage that accelerates the applications of electric vehicles and portable electronics and complements current battery technologies. Unlike conventional capacitors, supercapacitors implement the electrochemical double layer capacitor and pseudocapacitor mechanisms to raise storage capabilities on a limited area thus the nanoporous structure can be utilized to boost capacities. Here we present preparation of nanoporous materials of nanoparticulate WO3/MoO3 films using green technologies of electro-exploding wire and spray coating techniques. Nanoporous structures of the films are simply extended with an increase of film thickness. Their energy storage capabilities are explored using cyclic voltammetry and galvanostatic charge-discharge measurements. It is unveiled that diffusion coefficients of ion intercalation and deintercalation exponentially increase with an increase of film thickness and the highest areal capacitance of 87.3 mF/cm2 is achieved at a discharging current of 0.1 mA/cm2. In addition, the nanoparticulate WO3/MoO3 films present a good charging-discharging retention ability, up to 67%. Such impressive energy storage capabilities of WO3/MoO3 composite films can be exploited for high-performance supercapacitive applications.