Graphene Supported Platinum-Cobalt Nanocomposites As Electrocatalysts for Borohydride Oxidation

In relation to other types of fuel cells direct borohydride fuel cells (DBFCs) are of particular value for their high theoretical capacity and specific energy density, i.e. 5.6 Ah/g and 9.3 Wh/g for NaBH₄, respectively. For reducing the amount of Pt, transition metals such as Ni, Co, Fe, Cu have been added as alloy metals to the Pt-based catalysts. Recently, graphene as catalyst support has incurred intense interest in fuel cell applications due to its unique, outstanding physicochemical properties, such as an extremely high specific surface area (2600 m²g^–1).

A rapid microwave heating method was used to prepare the graphene supported PtCo catalysts with the Pt:Co molar ratio 1:7, 1:22 and 1:44. TEM and ICP-OES were employed to characterize the morphology and composition of catalysts. The electrocatalytic activity of the synthesized catalysts towards the oxidation of borohydride was investigated by means of the cyclic voltammetry and chronoamperometry. The kinetics of the catalytic hydrolysis of NaBH₄ in the presence of the synthesized catalysts was also investigated.

It was found that Pt nanoparticles of about 1-3 nm in size were successively deposited onto the surface of graphene nanosheets. Pt nanoparticles were uniform and well dispersed on the surface of graphene. The EDX spectra confirm the presence of Pt and Co nanoparticles in the investigated PtCo/GR catalysts.

The Pt loadings were 0.125 mg Pt cm^–2 in the Pt/GR and 0.165, 0.144 and 0.125 mg Pt cm^–2 in the synthesized PtCo/GR having the Pt:Co molar ratio 1:7, 1:22 and 1:44, respectively. It has been determined that the synthesized graphene supported PtCo catalysts show an enhanced electrocatalytic activity towards the oxidation of H₂ generated by catalytic hydrolysis of BH₄^– and direct oxidation of BH₄^– ions comparing with the graphene supported bare Pt and Co catalysts. The graphene supported PtCo catalyst having the Pt:Co molar ratio 1:44 exhibits the highest electrocatalytic activity for the both oxidation reactions of H₂ and BH₄^– ions.

 

Acknowledgement

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