Enhanced electrochemical performance of Co-V-O-N by a synergistic effect for aqueous asymmetric supercapacitors.

• Electrochemical performance was greatly improved by the Co-V optimization strategy. • The Co-based species effectively avoids the agglomeration and facilitates fully electrochemical reaction. • V-based species owning abundant valence state improves the electrochemical activity. • CH-V16 provides high specific capacitance of 6.26F cm−2 at a current density of 10 mA cm−2. • CH-V16//CC shows high energy density of 0.347 mWh cm−2 at 4 mW cm−2 and excellent cycling performance. Insufficient utilization, low conductivity and sluggish kinetics of Co and V-based oxides usually hinder their practical application in supercapacitors. In this study, we employ a simple two-step hydrothermal process to obtain Co-V binary metal composites (Co-V-O-N, a composite comprising CoVO 3 , VO 2 (H 2 O) 0.5 , (NH 4) 0.38 V 2 O 5 , NH 4 V 10 O 25 ·8H 2 O). After optimizing the reaction time between the Co-based precursor (CH) and the subsequently grown V species, the optimal synergistic combination of these two components effectively avoids the agglomeration of the active materials and enhances the conductivity of electrode conductivity. Accordingly, the obtained CH-V16 electrode achieves a high areal capacitance of 6.26F cm−2 at 10 mA cm−2, excellent rate capability with 67 % capacitance retention when the current density is increased from 5 to 60 mA cm−2, much better than the electrodes only with one component. In addition, an asymmetric supercapacitor constructed with CH-V16 and conductive carbon cloth shows a high energy density of 0.347 mWh cm−2 at 4 mW cm−2 as well as impressive cyclic performance by remaining 90 % of the initial specific capacitance over 20,000 cycles at 30 mA cm−2. This work offers a perspective to design high-performance Co-V binary metal oxides for asymmetric supercapacitors by a synergistic combination. [ABSTRACT FROM AUTHOR]