Fine-tuning the surface coverage of niobium oxide on platinum catalysts and its impact on the oxygen reduction reaction

Abstract

Platinum electrocatalysts coated with an ultrathin film of niobium oxide, which were prepared with a fine-tuned surface coverage, were evaluated for their influence on the oxygen reduction reaction. A series of ultrathin (<10 nm thick), patterned coatings of niobium oxide were prepared on planar platinum substrates using a combination of atomic layer deposition, photolithography, and wet-chemical etching techniques. Atomic layer deposition enabled a high degree of control over the thickness of the niobium oxide coating. Niobium oxide is a corrosion-resistant material that can improve the stability of electrocatalysts. A balance is sought, though, between the stabilizing benefits of applying a metal oxide coating to electrocatalysts and the possible blockage of catalytically active sites. The study presented herein pursues a method to precisely tune the surface coverage of niobium oxide coatings using techniques to pattern these coatings on a platinum electrocatalyst. The prepared catalysts were evaluated using a range of electrochemical and microscopy techniques. It was found that catalysts with higher coverages of niobium oxide had a higher initial resistance towards the oxygen reduction reaction but significantly outperformed the long-term performance of the uncoated, pristine platinum catalyst.