A method for the incorporation of immobile oxygen-containing functional groups onto multi-walled carbon nanotubes (MWCNTs) rooted in a metallic substrate for supercapacitor (SC) application is presented. Direct growth on the current collector (a 316 stainless steel (SS) mesh) offers the benefit of minimal MWCNT agglomeration, avoidance of using binder, and maintaining the 3-dimensional nanostructure. MWCNTs are grown by thermal-chemical vapour deposition (t-CVD) using SS as substrate and functionalized using an Ar/C2H6/O-2 glow discharge. When used as a binder-free SC electrode, these functionalized MWCNTs (f-MWCNTs) show excellent surface stability and large specific capacitance values. At low charging/discharging current densities (0.2 mA cm (-2) or 3 A g (-1)), a specific capacitance of 288 +/- 10 F g (-1) is achieved. The material shows good rate capability up to charging/discharging current density of 10 mA cm (-2) (37 A g (-1)) and displays excellent reversibility. Consequently, these new binder-free f-MWCNT SC electrodes are excellent candidates for future investigations of MWCNT-based SC electrodes. (C) 2014 Elsevier Ltd. All rights reserved.