Vertically-oriented graphene electrodeposited with MnO₂ on native SiO₂/Si for high-performance supercapacitor electrodes

Supercapacitor electrodes, composed of vertically-oriented graphene (VG) and MnO₂, are synthesized on native SiO₂-passivated silicon wafers. The VG layers with a thickness of ~3 μm are deposited directly on the substrates via plasma-enhanced chemical vapor deposition (PECVD). The distribution levels of MnO₂ formed with the electrodepositing method are investigated by using different types of solutions. The deeper infiltration of MnO₂ depositions produced with ethanol/water solution is observed. The capacitance retention of 75.22% from a scan rate of 20 mV/s to 100 mV/s with ethanol/water solution, compared with that of 60.72% using water solution, suggests the better rate capability. The specific capacitance as high as 470.80 mF/cm² at 20 mV/s is achieved with the increasing loadings of MnO₂. The original retention of 99.29% after 5000 cycles demonstrates the excellent cycling stability, which is ascribed to the strong bonds between VG/SiO₂/Si and MnO₂/VG. The promising supercapacitor electrodes in this study provide a potential for forming high-performance supercapacitor devices based on silicon wafer substrates.