Tantalum (oxy)nitrides prepared using reactive sputtering for new nonplatinum cathodes of polymer electrolyte fuel cell

Tantalum (oxy)nitrides (TaOxNy) have been investigated as new cathodes for polymer electrolyte fuel cells without platinum. TaOxNy films were prepared using a radio frequency magnetron sputtering under Ar + O2 + N2 atmosphere at substrate temperatures from 50 to 800 °C. The effect of the substrate temperature on the catalytic activity for the oxygen reduction reaction (ORR) and properties of the TaOxNy films were examined. The catalytic activity of the TaOxNy for the ORR increased with the increasing substrate temperature. The ORR current density at 0.4 V vs. RHE on TaOxNy prepared at 800 °C was approximately 20 times larger than that on TaOxNy prepared at 50 °C. The onset potential of the TaOxNy for the ORR was obtained at the ORR current density of −0.2 μA cm−2. The onset potential of the TaOxNy prepared at 800 °C was ca. 0.75 V vs. RHE. The X-ray diffraction patterns revealed that Ta3N5 structure grew as the substrate temperature increased. While, the ionization potentials of all specimens were lower than that of Ta3N5, and decreased with the increasing substrate temperature. The TaOxNy which had Ta3N5 structure and lower ionization potential might have a definite catalytic activity for the ORR.