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

Abstract

Tantalum (oxy)nitrides (TaO x N y ) have been investigated as new cathodes for polymer electrolyte fuel cells without platinum. TaO x N y films were prepared using a radio frequency magnetron sputtering under Ar + O 2 + N 2 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 TaO x N y films were examined. The catalytic activity of the TaO x N y for the ORR increased with the increasing substrate temperature. The ORR current density at 0.4 V vs. RHE on TaO x N y prepared at 800 °C was approximately 20 times larger than that on TaO x N y prepared at 50 °C. The onset potential of the TaO x N y for the ORR was obtained at the ORR current density of −0.2 μA cm −2. The onset potential of the TaO x N y prepared at 800 °C was ca. 0.75 V vs. RHE. The X-ray diffraction patterns revealed that Ta 3N 5 structure grew as the substrate temperature increased. While, the ionization potentials of all specimens were lower than that of Ta 3N 5, and decreased with the increasing substrate temperature. The TaO x N y which had Ta 3N 5 structure and lower ionization potential might have a definite catalytic activity for the ORR.