Self-Supported Pt-Ni Mesostructures as Ultrastable Oxygen Reduction Reaction Electrocatalysts in Proton Exchange Membrane Fuel Cell

Abstract

Improving the activity and durability of the cathode catalyst in proton exchange membrane fuel cells (PEMFCs) is of great importance for their commercialization. The most prevalent commercial catalysts are Pt-based nanoparticles, which are finely dispersed on high surface area carbon supports (Pt/C). During the fuel cell operation, considerable activity loss of Pt/C occurs because of corrosion of carbon support material, the dissolution of Pt, and the detachment of Pt nanoparticles from the carbon support. In this work, support-free 3D mesostructured spherical Pt-Ni alloy electrocatalysts (Meso-PtNi) of 100 nm in size were prepared by nanocasting mesoporous silica nanospheres (MSNs). Interestingly, hightemperature annealing at 600 °C afforded the formation of PtNi intermetallic ordered phase while reduction at 300 °C generated disordered Pt-Ni alloy phase. Electrocatalytic activity and stability of Meso-PtNi for the oxygen reduction reaction (ORR) was investigated in 0.1 M HClO4. Meso-PtNi catalysts showed enhanced performance in ORR measurement compared to Pt/C, Pt black, and Meso-Pt. Importantly, Meso-PtNi containing intermetallic phase exhibited better activity than disordered alloy structure. An accelerated degrading test (ADT) was conducted according to the US Department of Energy’s protocol. Meso-PtNi showed superior stability as compared to the commercial Pt/C and Pt black catalysts, up to 30,000 potential cycling. Particularly, the Meso-PtNi with intermetallic phase showed a remarkable stability. It was found that Meso-PtNi was activated during the early stage of ADT, and retained its increased ORR activity up to 50,000 cycling. We fabricated membrane electrode assembly based on the intermetallic Meso-PtNi cathode, and achieved the excellent single cell performance in PEMFC.