Characterization of Au and Bimetallic PtAu Nanoparticles on PDDA-Graphene Sheets as Electrocatalysts for Formic Acid Oxidation

Abstract

Nanocomposite materials of the Au nanoparticles (Au/PDDA-G) and the bimetallic PtAu nanoparticles on poly-(diallyldimethylammonium chloride) (PDDA)-modified graphene sheets (PtAu/PDDA-G) were prepared with hydrothermal method at 90 °C for 24 h. The composite materials Au/PDDA-G and PtAu/PDDA-G were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for exploring the structural characterization for the electrochemical catalysis. According to TEM results, the diameter of Au and bimetallic PtAu nanoparticles is about 20-50 and 5-10 nm, respectively. X-ray diffraction (XRD) results indicate that both of PtAu and Au nanoparticles exhibit the crystalline plane of (111), (200), (210), and (311). Furthermore, XRD data also show the 2°-3° difference between pristine graphene sheets and the PDDA-modified graphene sheets. For the catalytic activity tests of Au/PDDA-G and PtAu/PDDA-G, the mixture of 0.5 M aqueous H2SO4 and 0.5 M aqueous formic acid was used as model to evaluate the electrochemical characterizations. The catalytic activities of the novel bimetallic PtAu/graphene electrocatalyst would be anticipated to be superior to the previous electrocatalyst of the cubic Pt/graphene.

Keywords: Au nanoparticle; Bimetallic PtAu nanoparticle; Formic acid oxidation; Graphene; PDDA.

Fig. 1

TEM and XRD results of Au/PDDA-G electrocatalyst, at a low magnification; b high-resolution TEM and lattice image analysis; c intermediate magnification; d XRD pattern

Fig. 2

TEM and XRD results of PtAu/PDDA-G electrocatalyst, at a low magnification; b high-resolution TEM image; c SAED pattern; d XRD pattern

Fig. 3

TGA results of Au/PDDA-G and PtAu/PDDA-G electrocatalysts

Fig. 4

XPS spectra of Au 4f and Pt 4f binding energies in the Au/PDDA-G and PtAu/PDDA-G electrocatalyst

Fig. 5

The electrochemical study in aqueous 0.5 M H₂SO₄ + 0.5 M HCOOH. a The cyclic voltammetric study in 0.5 M aqueous H₂SO₄. The inset is the same electrical chemical study for Au nanoparticles. b The HCOOH oxidation test for three electrocatalysts in 0.0–1.0 V range. The numbers are the area ratios with respect to the dash baselines. The inset is the test for Au/PDDA and Au, respectively

Fig. 6

EIS and fitting results for Au/PDDA-G and PtAu/PDDA-G electrocatalysts. The upper and lower insertions depict equivalent circuit simulations for Au/PDDA-G and PtAu/PDDA-G electrocatalysts, respectively

Fig. 7

The electrochemical catalysts durability test for formic acid oxidation at the potential 300 mV for about 3000 s. The blue line is the result for PtAu/PDDA-G, the black line is for cubic Pt (60 wt.%)/G, and the yellow line is for Au/PDDA-G