Bimetallic Pd–Rh nanoparticles onto reduced graphene oxide nanosheets as electrocatalysts for methanol oxidation

• This study adopts a microwave method to deposit Pd–Rh catalysts on graphene sheets.
• The Pd:Rh ratio is chosen as a crucial factor to examine the catalytic activity.
• The Pd–Rh catalyst (with Pd:Rh ratio = 75:25) displays the highest alloying degree.
• More Pd–Rh pairs induce high CO tolerance level and superior cyclic durability.
• The Pd–Rh catalyst shows lower diffusion resistance, as compared with pure Pd one.

An advanced electrode for methanol oxidation in alkali medium, comprising Pd–Rh nanoparticles and reduced graphene oxide (r-GO) sheets, has been successfully synthesized by pulse microwave polyol (MP) technique. The MP technique is capable of depositing Pd–Rh nanoparticles on the surface of r-GO sheets under microwave irradiation. The atomic ratio of Pd:Rh is chosen as a crucial factor to examine the catalytic activity toward H adsorption/desorption and methanol oxidation. The Pd–Rh catalyst (with Pd:Rh ratio = 75:25) displays the highest alloying degree (~ 41.5%), favoring the formation of Pd–Rh pairs in the binary crystals. On the Pd–Rh catalyst, the Pd site acts as major contributor toward hydrogen adsorption and methanol oxidation, whereas the neighboring Rh site serves as a promoting center to strip oxygenate species (e.g., Pd − (CO)ads sites). The enhanced catalytic activity on the Pd–Rh catalyst is attributed to the fact that the binary catalyst possesses a high alloying degree, leading to high catalytic coverage, high-level of CO tolerance, and superior cyclic durability. The Tafel slope of as-made Pd–Rh catalyst could reach as low as 63 mV dec− 1 among the electrodes, based on the analysis of Tafel plots. The Pd–Rh catalyst also exhibits both lower equivalent diffusion resistance and equivalent series resistance, as compared with pure Pd one.