Tailored Electron Transfer Pathways in Au_(core)/Pt_(shell)–Graphene Nanocatalysts for Fuel Cells

摘要

Au-core/Pt-shell-graphene catalysts (G-Cys-Au@Pt) are prepared through chemical and surface chemical reactions. Au-Pt core-shell nanoparticles (Au@Pt NPs) covalently immobilized on graphene (G) are efficient electrocatalysts in low-temperature polymer electrolyte membrane fuel cells. The 9.5 +/- 2 nm Au@Pt NPs with atomically thin Pt shells are attached on graphene via l-cysteine (Cys), which serves as linkers controlling NP loading and dispersion, enhancing the Au@Pt NP stability, and facilitating interfacial electron transfer. The increased activity of G-Cys-Au@Pt, compared to non-chemically immobilized G-Au@Pt and commercial platinum NPs catalyst (C-Pt), is a result of (1) the tailored electron transfer pathways of covalent bonds integrating Au@Pt NPs into the graphene framework, and (2) synergetic electronic effects of atomically thin Pt shells on Au cores. Enhanced electrocatalytic oxidation of formic acid, methanol, and ethanol is observed as higher specific currents and increased stability of G-Cys-Au@Pt compared to G-Au@Pt and C-Pt. Oxygen reduction on G-Cys-Au@Pt occurs at 25 mV lower potential and 43 A g(Pt)(-1) higher current (at 0.9 V vs reversible hydrogen electrode) than for C-Pt. Functional tests in direct fomic acid, methanol and ethanol fuel cells exhibit 95%, 53%, and 107% increased power densities for G-Cys-Au@Pt over C-Pt, respectively.