Co-C-N and Fe-C-N thin film catalysts have been modified by controlled doping with boron. Corresponding novel thin film catalysts Co-C-N-B and Fe-C-N-B were synthesized by combinatorial magnetron sputter deposition in an Ar/N-2 gas mixture followed by subsequent heat-treatment between 700 and 1000 degrees C in an argon atmosphere. The nitrogen content of the as-prepared thin film catalysts Could be increased by the addition of boron. Furthermore, the amount of remaining nitrogen in heat-treated catalyst samples was significantly higher in case of boron containing samples. The thin film catalysts were characterized by means of X-ray diffraction (XRD) analysis, electron microprobe and electrochemical measurements. For electrochemical studies the activity as oxygen reduction reaction (ORR) catalyst was investigated using the rotating ring-disk electrode (RRDE) technique in 0.1 M HClO4 solution at room temperature. The catalytic activity Was found to decrease with the boron content in the thin film catalysts even though the N-content increased. (c) 2007 Elsevier Ltd. All rights reserved.