Investigation of Borohydride Oxidation on Graphene Supported Gold-Copper Nanocomposites

Graphene as catalyst support has incurred intense interest in fuel cell applications due to its unique, outstanding physicochemical properties. Pure gold and gold-based catalysts show an enhanced electrocatalytic activity towards the direct oxidation of borohydride. Combination of graphene and gold-based catalysts allows reducing the amount of noble metal and fabricating novel materials with high efficiency towards borohydride electro-oxidation.

In this study the graphene supported AuCu catalysts (denoted as AuCu/GR) with different Au:Cu molar ratio were prepared by microwave heating of Au(III) and Cu(II) salts in ethylene glycol (EG) solutions at 150 ^oC for 30 min. It has been determined that the composition of AuCu/GR catalysts depends on pH of reaction mixture. When the reaction mixture pH was 7.0, 10.1 and 12.2, the AuCu/GR catalysts having the Au:Cu molar ratio 37:1, 1:13 and 1:32, respectively, were synthesized. The morphology, structure and composition of the prepared catalysts were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD) and inductively coupled optical emission spectroscopy (ICP-OES). The electrocatalytic activity of the synthesized catalysts was investigated towards the oxidation of borohydride by means of cyclic voltammetry and chronoamperometry.

It was found that Au nanoparticles were successively deposited onto the surface of graphene nanosheets. Au nanoparticles were uniform and well dispersed on the surface of graphene. The analysis of composition of the prepared AuCu/GR catalysts by means of ICP-OES confirms the presence of Au and Cu.

The Au loadings were 0.055 mg Au cm^–2 in the Au/GR and 0.107, 0.091 and 0.088 mg Au cm^–2 in the synthesized AuCu/GR catalysts having the Au:Cu molar ratio 37:7, 1:13 and 1:32, respectively. It has been determined that the graphene supported AuCu catalysts show an enhanced electrocatalytic activity towards the oxidation of BH₄^– ions comparing with the graphene supported bare Au catalyst and graphene supported bare Cu catalyst. Furthermore, borohydride oxidation current densities at the graphene supported AuCu/GR catalysts having the Au:Cu molar ratio 1:12 and 1:32 are ~13 times higher than those obtained at the AuCu/GR catalyst with the Au:Cu molar ratio 37:1.

Acknowledgement

This research was funded by a Grant (No. ATE-08/2012) from the Research Council of Lithuania.