Bimetallic PdM (M = Fe, Ag, Au) alloy nanoparticles assembled on reduced graphene oxide as catalysts for direct borohydride fuel cells

Abstract

The development of highly active and inexpensive electrode materials is crucial to improve the performance of fuel cells and to boost their commercialisation. In this work, a series of bimetallic palladium alloy nanoparticles assembled on reduced graphene oxide, namely PdFe/rGO, PdAg/rGO and PdAu/rGO, was prepared and tested for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) in alkaline media. The morphology and structure of the as-prepared PdM alloy NPs and PdM/rGO electrocatalysts were characterised by XRD, TEM, XPS and ICP-MS and their electrochemical activity was investigated by cyclic and linear scan voltammetry, chronoamperometry, and rotating disc electrode measurements. Among the tested electrocatalysts, PdAu/rGO demonstrated the best performance by providing high current densities for both ORR and BOR. The number of electrons exchanged during ORR at PdAu/rGO, PdAg/rGO and PdFe/rGO electrocatalysts was calculated to be 4.0, 2.8 and 2.0, whereas Tafel slopes were evaluated to be 0.202, 0.182 and 0.173 V dec−1, respectively. BOR at PdAu/rGO and PdFe/rGO proceeds with 5.5 and 2 electrons exchanged, respectively, and the reaction order ranged from 0.4 for PdAg/rGO to 1 for PdAu/rGO. Furthermore, effect of temperature was studied and BOR activation energy determined to be 23 kJ mol−1.