Heteroatom doping of carbon nanostructures is a convenient tool to control their physicochemical properties and to make them suitable for various applications. Carbon nano‐onions (CNOs) doped with nitrogen (N‐CNOs) have been prepared by annealing aminated‐nanodiamond particles (AM‐NDs) at different temperatures (1150, 1450 and 1650 °C) in an inert He atmosphere. Their physicochemical properties were compared with those of pristine CNOs obtained from non‐functionalized NDs under the same experimental conditions. The carbon nanostructures were characterized using transmission (TEM) and scanning (SEM) electron microscopy, X‐ray powder diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, porosimetry, and differential‐thermogravimetric analyses (TGA‐DTG). Their physicochemical properties are systematically discussed for undoped and for the nitrogen‐doped CNO samples. The results reveal that the surface morphology and the structure of undoped and nitrogen‐doped CNOs vary with the annealing temperature. All of these materials were electrochemically tested as electrode materials for enzyme‐free catalysis of hydrogen peroxide. The nitrogen‐doped carbon nanostructures have a higher catalytic activity than undoped nanostructures obtained under the same experimental conditions.