In this work we present a simple and efficient method of nitrogen plasma modification of carbon nanotubes (CNTs). The process allows for treatment of the nanotubes in the form of powder with quite a high yield (65 mg of CNTs per hour). The modified carbon nanotubes contain approx. 3.8% nitrogen, mostly in the pyridinic form. Plasma treated CNTs exhibit better dispersibility in water and higher electric capacitance than pristine CNTs. Modified CNTs are a proper component of novel nanocomposites based on the conducting polymer poly(3,4-ethyleneidoxythiophene). Electrodeposited thin layers of the nanocomposite exhibit improved electrochemical properties (higher capacitance, better stability, lower resistance, faster diffusion) compared to the pure polymer layers.

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The long cycle life stability and high energy density are limiting broader feasible applications of supercapacitors (SCs). The novel diamondized titania nanocomposite SCs deliver high power and energy densities along with high capacitance retention rates. SC electrodes were fabricated utilizing a combination of Ti anodization followed by chemical vapor deposition resulting in the simultaneous growth of the complex boron-doped diamond (BDD)/TiC interface. The first-principles simulations along with extended molecular investigations conducted by bright-field transmission electron microscopy and high resolution-scanning electron microscopy revealed that capacitive phenomena are delivered by nanoporous, multifaceted, and substoichiometric TiC, forming clusters at the lateral surfaces of titania nanotubes. Next, TiC mechanical stability and effective charge transfer electrode–electrolyte are efficiently provided by the highly conductive, although discontinuous BDD overlayer. The assembled two-electrode SC devices exhibited capacitances of 15 mF cm–2, which were stable at 0.1 V s–1 scan rate in various neutral aqueous electrolytes. The composite TiO2 nanotube arrays-BDD SCs showed outstanding long-term cycling stability with a capacitance retention of 93% after 100,000 chronopotentiometry cycles verified by postaging cyclic voltammetry tests. In parallel, the energy and power density calculated at a current density of 3 A g–1 achieved levels as high as 14.74 W h kg–1 and 24.68 kW kg–1, revealing the superior performance of the assembled devices compared to recently reported SCs.