Glad-SAD Pt-Ni Alloy/Ni Nanorods As Highly Active Oxygen Reduction Reaction Electrocatalysts

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) have drawn significant attention as alternatives to traditional power sources, especially in automotive applications, due to their high energy conversion efficiency, zero emissions, and system robustness.1 However, the sluggish kinetics of oxygen reduction reaction (ORR) on the cathode demand a high loading of active platinum (Pt) or Pt-rich alloy catalysts,2 which increases the cost of PEMFC systems. Cost reductions can be achieved by increasing the ORR kinetics of platinum-based catalysts and by more efficient utilization of the platinum component of the catalyst. In addition, the limited durability of standard and advanced ORR electrocatalysts, associated with corrosion of the catalyst particles and support,3 ,4 remains a major obstacle. The development of carbon-free catalysts could address degradation issues associated with the carbon support. Relying on the high area-specific ORR activity of Pt thin films,4 electrocatalysts comprised of thin continuous Pt or Pt-alloy layers on patterned non-precious metal nanorod substrate supports could result in reductions in Pt loading due to both higher Pt utilization and higher ORR activity while also mitigating the stability issues associated with carbon supports. In this work, well-adherent and continuous Pt-Ni thin films, with several different molar ratios of Pt to Ni were deposited on Ni nanorods (NRs) by combining the glancing angle deposition (GLAD) technique5 for the deposition of Ni-NRs and small angle deposition (SAD) technique6 for the deposition of a thin conformal coating of Pt-Ni on the Ni-NRs (designated Pt-Ni@Ni-NRs). The Pt-Ni@Ni-NRs structures were supported on glassy carbon for evaluation of ORR activity in aqueous acidic electrolyte using the rotating disk electrode technique. These Pt-Ni@Ni-NRs catalysts showed superior area-specific and mass activities for ORR compared to PtNi nanorod catalysts7 that were prepared using the GLAD technique.