The wettability and the hydrophilic nature of S doped carbon materials are also presumed to be responsible for the increased capacitive performance. It has been reported that the S-doped carbon nano-onion based symmetric cell exhibits an increased specific capacitance of 305 F g - 1 at 2 A g -1 [189]. The sulphur atom in the pores withdraw ions from the electrolyte by introducing positive charge over the adjacent carbon atoms. As a result, charge transfer between the sulphur and carbon is favoured that enhances the surface wettability and chargestorage characteristics. Additionally, the S-doped carbon nano-onion exhibits the water wetting angle of 48° and attributed to the fact that the excellent surface wettability permits the increased interactions from the electrolyte ions to the exposed surfaces via surface adsorption, that improves the formation of electric double layers.