Comparative study of Pd-based electrocatalysts decorated on hybrid carbon supports towards methanol oxidation

Abstract

One suitable strategy to improve the utilisation and performance of Pd-based catalysts in direct methanol fuel cells (DMFCs) is by combining or blending carbon supports. In this study, Pd nanoparticles (NPs) were decorated on bi-hybrid carbon supports consisting of carbon nanotubes (CNTs), graphene nanoplates (GNPs) and carbon black (XC-72) with varying ratios of CNTs: GNPs, CNTs: XC-72 and XC-72: GNPsthrough microwave-assisted ethylene glycol (EG) reduction. All as-prepared catalysts were characterisedby Transmission Electron Microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their electrocatalytic activities towards methanol oxidation reaction (MOR) in alkaline solution were investigated by electrochemical measurements. Results indicated that the use of hybrid supports for catalysts substantially increases the electrochemical surface area, reduces the overpotential to methanol oxidation and improves kinetic performance. These effects can be attributed to the unique structure formed after mixing that allows for complete surface utilisation.Among the bi-hybrid electrocatalysts, Pd/CNT-GNP (1:0.1), Pd/CNT-XC-72(1:0.2) and Pd/XC-72-GNP (1:0.2) catalysts have higher activity and better performance.Particularly, Pd/CNT-GNP (1:0.1) catalyst shows a superior activity and the highest oxidation peak current density towards MOR at 57.34 mA/cm2.TEM and XRD results show that the catalyst nanoparticles on the bi-hybrid carbon support have good dispersion, are not agglomerated and havea small particle size. Hence, the catalyst exhibits an optimised performance and long stability towards methanol electrooxidation in alkaline media.