As part of an ongoing effort to develop novel, highly active and stable Pt-free catalysts for the oxygen reduction reaction (ORR), we here report the synthesis, structural characteristics and electrochemical/electrocatalytic properties of novel core-shell composite materials, consisting of a spherical nitrided carbon core and a tantalum (oxy)nitride shell. The (nitrided) carbon core is supposed to improve the electrical conductivity of the material and the (oxy)nitride shell is intended to protect the core against electrochemical corrosion. Spherical core-shell TaOxNy@CmNn composite particles were synthesized by sol-gel deposition of tantalum oxide on preformed carbon spheres, which were prepared by hydrothermal carbonization of glucose and subsequent nitriding in ammonia vapor at different temperatures (700 degrees C - 1150 degrees C). The influence of the nitriding temperature on the structure and phase composition of the resulting composite particles was evaluated, employing a variety of techniques, including electron microscopy (SEM, TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), elemental analysis, thermogravimetric analysis (TGA), IR spectroscopy and N-2 sorption measurements, and correlated with changes in the electrochemical/electrocatalytic behavior. These core-shell composite materials show a significantly improved ORR activity compared to pure tantalum (oxy)nitrides, in particular upon nitriding at 1000 degrees C, while the selectivity for the 4-electron pathway to H2O still requires improvement. The physical origin of the high activity of these materials and contributions from different phases are discussed. (C) 2016 Elsevier Ltd. All rights reserved.