In situ growth of self-supported and defect-engineered carbon nanotube networks on 316L stainless steel as binder-free supercapacitors.

Self-supported and defect-engineered carbon nanotube networks directly grown on 316L stainless steel are used for binder-free supercapacitors. In situ growth of the carbon nanotube networks on 316L stainless steel is obtained through the chemical vaporization deposition and thermal treatment to generate various defects. The relationship between the microstructures of carbon nanotube networks and electrochemical characteristics is investigated. The as-prepared carbon nanotube networks are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman analysis. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy tests are also carried out to evaluate their capacitive properties, suggesting that the electrochemical characteristics are significantly affected by annealing time. The carbon nanotube networks annealed at 500 C for 2 h display high capacitance of 11 mF cm and excellent cycling lifetime with capacitance retention ration 97% at the scan rate of 0.5 mA cm for 5000 periods, which is attributed to the defect engineering increasing the defects of carbon nanotube networks, enhancing hydrophilic property and facilitating the transportation of electrolyte ions.