Methanol-tolerant Pd nanocubes for catalyzing oxygen reduction reaction in H2SO4 electrolyte

New methanol-tolerant catalysts in the form of 27 nm, 48 nm, and 63 nm palladium nanocubes enclosed by {1 0 0} facets were successfully used for the oxygen reduction reaction (ORR) in a 0.5 M H2SO4(aq) solution. Based on X-ray photoelectron spectroscopy and high resolution transmission electron microscopy analyses, the surface of the smallest Pd nanocubes was easily oxidized to PdO. The data provided by the analysis of a mass-transfer-corrected Tafel curve in a free methanol electrolyte showed that the specific activities of the 27 nm, 48 nm, and 63 nm Pd nanocubes at 0.65 V (vs. Ag/AgCl) in terms of the kinetic current density (jk) were 11.51 × 10−2 mA cm−2, 12.32 × 10−2 mA cm−2, and 10.06 × 10−2 mA cm−2, respectively. In contrast, Pd and Pt nanoparticles featured specific activities of 3.7 × 10−2 mA cm−2 and 13.2 × 10−2 mA cm−2, respectively. Further Tafel analyses conducted using a rotating ring-disk electrode in a methanol electrolyte showed that the jks of the 27 nm, 48 nm, and 63 nm Pd nanocubes at 0.65 V (vs. Ag/AgCl) were 14.87 × 10−2 mA cm−2, 16.55 × 10−2 mA cm−2, and 12.98 × 10−2 mA cm−2, respectively. The nanocubes have a high activity toward the ORR; the greatest jk was occurred on the 48 nm nanocube even larger than 5.65 × 10−2 mA cm−2, the jk of the Pd nanoparticles in the methanol electrolyte, where Pt nanoparticles effected methanol oxidation in preference to the ORR. Despite working in methanol-tolerant solutions, the prepared 48 nm Pd nanocubes exhibited high electroactivity.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pd nanocubes were successfully used as methanol-tolerant catalysts for acidic oxygen reduction. ► Based on XPS and HRTEM analyses, the surface of the smallest Pd nanocubes was easily oxidized to PdO. ► Despite working in methanol-tolerant solutions, these cubic catalysts have a high activity. ► The greatest activity was occurred on the 48 nm nanocube in the methanol electrolyte.