VO2 nanoflake arrays for supercapacitor and Li-ion battery electrodes: performance enhancement by hydrogen molybdenum bronze as an efficient shell material†
Hydrogen molybdenum bronze (HMB) is electrochemically deposited as a homogeneous shell on VO2 nanoflakes grown on graphene foam (GF), forming a GF + VO2/HMB integrated electrode structure. Asymmetric supercapacitors based on the GF + VO2/HMB cathode and neutral electrolyte are assembled and show enhanced performance with weaker polarization, higher specific capacitance and better cycling life than the unmodified GF + VO2 electrode. Capacitances of 485 F g−1 (2 A g−1) and 306 F g−1 (32 A g−1) are obtained because of the exceptional 3D porous architecture and conductive network. In addition, the GF + VO2/HMB electrodes are also characterized as the cathode of lithium ion batteries. Very stable capacities at rates up to 30 C are demonstrated for 500 cycles. This new type of shell material is expected to have its generic function in other metal oxide based nanostructures.