Effect on percolation threshold of catalytic layer: Pt/N-Doped graphene shell onto SWCNT for ORR electrode

A high-rate oxygen reduction reaction (ORR) is necessary for polymer electrolyte membrane fuel cells (PEMFC). In this work, by using a solution plasma technique, Pt catalytic particles coated with N-doped graphene (Pt-NG) were effectively produced at 25°C. According to transmission electron microscope images, the average diameter of Pt particles was 4 nm, while the graphene layer thickness was less than 1 nm. A catalytic layer of Pt-NG supported on single-walled carbon nanotubes (Pt-NG/SWCNT) was synthesized. Cyclic voltammetry was used to assess the ORR characteristics of Pt-NG/SWCNT catalytic layers. Only at a density of SWCNT to solvent ratio of 0.75 mg ml⁻¹ were the ORR peaks clearly visible. Because of the high resistivity of SWCNT layers, the ORR peaks in other ranges, 0.4 mg ml⁻¹ to 2.0 mg ml⁻¹, were not clearly observed. The effect of SWCNT concentration on conductivity was proven to follow the basic concept of the percolation threshold.