Reduced graphene oxide/VSB-5 composite micro/nanorod electrode for high energy density supercapattery

Nickel Phosphate (Ni₂₀[(OH)₁₂(H₂O)₆][(HPO₄)₈(PO₄)₄]•12H₂O) – VSB-5 nano/micro rods composite with reduced graphene oxide (rGO) was successfully synthesized using a Polyvinyl Pyrrolidone (PVP) aided hydrothermal technique and applied as a battery-type cathode for supercapatteries. The uniform meso/microporous structure provides more electro-active sites for surface redox reaction and nano-paths for electrolyte ion diffusion which can significantly improve the device performance. From the electrochemical analysis, it was found that VSB-5/rGO exhibited a specific capacity of 117.3 mAh g⁻¹ (1056.1 F g⁻¹) which was noticeably higher than the pristine VSB-5 (60.7 mAh g⁻¹) at 5 mA cm⁻². These excellent electrochemical performances may be due to rGO modification and well-defined nano/micro rods. Furthermore, supercapatteries were fabricated by pairing a commercially available activated carbon (AC) electrode with VSB-5/rGO as a positrode. The fabricated cell was tested and showed a high specific capacity of 86.8 mAh g⁻¹ (208.4 F g⁻¹) with 88% capacity retention after 5000 cycles. Finally, the assembled supercapattery delivered a maximum specific energy of 80.5 Wh kg⁻¹ at a power output of 2216.5 W kg⁻¹. In comparison with a pristine VSB-5 based device, the AC/VSB-5/rGO device shows remarkable electrochemical performance, demonstrating that VSB-5/rGO is a promising, new electrode material for high performance supercapatteries.