We have used bias-assisted microwave plasma chemical vapor deposition to synthesize (i) two-dimensional carbon nanowalls [(2D CNWs), monolayer] and (ii) three-dimensional carbon nanowalls [(3D CNWs), double-layer] on carbon cloth in a CH4/CO2 system. The specific surface area of the 3D CNW electrode (1580 m(2)/g) was considerably larger than that of the 2D CNW electrode (364 m(2)/g). This higher surface area and more porous structure of the 3D CNW electrode resulted in its capacitance reaching as high as ca. 198 F/g at a scan rate of 10 mV/s. Electrochemical measurements suggested that this 3D electrode is a promising material for application in electrical storage devices.