A comparison of three carbon nanoforms as catalyst supports for the oxygen reduction reaction

Abstract

Defective graphene nanosheets (GNSs), single-walled carbon nanotubes (SWCNTs), and herringbone graphite nanofibres (GNFs) were used as Pd3Pt1 catalyst supports for an oxygen reduction reaction (ORR). Raman spectroscopy and cyclic voltammetry analyses revealed oxygen-containing functional groups and physical defects on the surfaces of the SWCNTs, GNFs, and synthesised GNSs. Mass-transfer-corrected Tafel diagrams obtained in an O2-saturated electrolyte showed that the SWCNTs with a high curvature allowed for more surface Pt atoms; thus, these Pd3Pt1 catalysts are the first SWCNT system to promote the ORR. These catalysts, however, were slower than the GNS-supported catalysts after 0.875V (vs. SCE; saturated calomel electrode). In terms of the kinetic current density, the highest mass activity was found for the Pd3Pt1/GNS composites. Additionally, according to rotating-ring disk electrode (RRDE) measurements, the H2O production efficiencies for the Pd3Pt1/GNS, Pd3Pt1/SWCNT, and Pd3Pt1/GNF systems were 70.35%, 66.7%, and 9.58%, respectively. Among these carbon supports, Pd3Pt1 on GNS showed the greatest efficiency and durability for producing H2O via an approximate four-electron pathway; this efficiency was ascribed to metal-support interaction.