Size induced Extrinsic Pseudocapacitance in Ultrasmall CoMoO4 Nanocluster

CoMoO4 has been exploited as a battery material since it possesses a high theoretical capacity and battery-like charge/discharge behavior. In this work, diffusion-limited charge storage is modulated into capacitive contribution by engineering the particle size within the diffusive path length (∼2 nm). We describe a simple methodology of size-controlled synthesis of an ultrasmall (∼2 nm) CoMoO4-carbon nanocomposite for high-performance electrochemical supercapacitors with long-lasting stability. The nanocomposite with an equal weight composition (50-CoMo@AC) sample exhibits a maximum specific capacity of 565 C/g (156.9 mAh/g) at 1 A/g. An asymmetric full cell device composed of a 50-CoMo@AC nanocomposite as a cathode and active carbon as an anode exhibits a specific capacity of 110.4 C/g (30.7 mAh/g) at 1 A/g. Further, the device delivers an energy density (ED) of 32.4 Wh/kg at a power density (PD) of 315.4W/kg and ED of 25.6 Wh/kg at a PD of 2420 W/kg. The device preserves 87.5% capacity after 10 000 cycles. Such high performance of the composite is attributed to the high surface-to-volume ratio of the electroactive material and low interfacial charge transfer resistance. Further, active carbon offers enhanced dispersion and stabilizes the nanoclusters due to embedment into the carbon matrix. It also enables volume expansion and strain relaxation throughout the charge–discharge process. The present study suggests that CoMo@AC is a potential candidate for a high-performance electrochemical energy storage device.