Periodic Pt Nanorod Arrays with Controlled Porosity for Oxygen Reduction Reaction

Nanorod arrays of platinum were fabricated on flat (Sample A) and patterned glassy carbon electrodes at room temperature using glancing angle deposition (GLAD) technique. Pt nanorod arrays were tested by cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques as a potential polymer electrolyte membrane fuel cell cathode electrode for oxygen reduction reaction (ORR). Patterned substrates with honeycomb geometry were obtained utilizing modified-nanosphere lithography method using polystyrene (PS) nanoparticles of diameters 250 (Sample B) and 500 (Sample C) nm. The RDE results demonstrate that samples B and C have higher diffusion limiting current density values of 5.8 and 6 mA/cm² at potential range of 0.2–0.7 V compared to 5.6 mA/cm² for sample A. ORR polarization curves show that the specific-area activity (SA), normalized to the Pt ECSA, of sample A at 0.9 V is about 1,060 μA/cm² that is about 18.7% higher than for the nanorods of sample B and C with SA of 893 μA/cm². However, samples B and C exhibit significantly higher specific-area activities at lower potentials, for example at 0.75 V, SA = 41,773 and 95,870 μA/cm², respectively, which are 2.8 and 6.5 times higher than 14,693 μA/cm² of sample A. The higher ORR activity at low potential region in the polarization curve of periodic and well-separated GLAD Pt nanorods is attributed to the enhanced electrode porosity which facilitates the oxygen mass transport to the active catalyst sites.