Nanopillar niobium oxides as support structures for oxygen reduction electrocatalysts

Metal oxides such as niobium oxides have been demonstrated as alternative support materials for Pt and non-precious metal catalysts in fuel cells. High surface area and columnar niobium oxide catalyst support structures were produced by the glancing angle deposition (GLAD) technique on 5 mm diameter glassy carbon disks. The columnar structures have lengths of about 500 nm, diameters of 50 nm and an areal density of about 109 cm−2. Annealing under different gas mixtures (Ar/H2) led to the formation of various oxides (Nb2O5, NbO2, or NbO + NbO2). Pt catalyst, with a loading of 0.1 mgPt cm−2, was deposited onto these structures by magnetron sputter deposition. Rotating disk electrode characterization of the samples, performed in 0.1M HClO4 electrolyte at room temperature, revealed surface enhancement factors of up to 11 and oxygen reduction specific activities of ≥1 mA cm−2Pt at 0.9 V (vs. RHE). The impact of annealing on Nb-O phase formation, conductivity, oxygen reduction activity and stability are discussed.