Design of Novel Graphene Materials as a Support for Palladium Nanoparticles: Highly Active Catalysts towards Ethanol Electrooxidation

The electrooxidation of ethanol in alkaline media by palladium (Pd) nanoparticles supported on 3D-Graphene nanosheets with varying morphological and physicochemical properties was investigated using potentiodynamic and potentiostatic techniques. 30 wt.% Pd electrocatalysts were synthesized using a surfactant-free soft alcohol reduction method (SARM) and deposited on thermally (7 at.% H2, 800 °C) and chemically reduced (N2H4·xH2O, 80 °C) 3D-Graphene nanosheets. The morphology of the nanosheets was modified using silica (L90 and EH5) sacrificial templates. For the sake of comparison, Pd nanoparticles were also deposited on a commercial carbon support (Vulcan) using SARM and physically characterized using X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The morphological and physicochemical properties of the 3D-Graphene supports were analyzed using Scanning Electron Microscopy (SEM), Nitrogen-sorption Brunauer–Emmett–Teller (BET), Energy-dispersive X-ray Spectroscopy (EDS) and Raman Spectroscopy. Our results show that thermally reduced 3D-Graphene nanosheets with a higher the degree of C-C sp2 hybridization improved the dispersion and reduced the average crystallite size of the Pd nanoparticles. Moreover, Pd nanoparticles supported on 3D-Graphene nanosheets modified with larger silica templates (L90) showed better tolerance towards poisoning species, possibly due to the larger pores etched into its matrix. Among the as-prepared catalysts, Pd nanoparticles of 6.3 nm supported on thermally reduced 3D-Graphene (BET surface area of 300 m2 g−1) exhibited the highest stability as well as peak current density of 1568 AgPd−1, which was about 1.5, 2.5 and 3 times greater than Pd nanoparticles supported on chemically reduced 3D-Graphene, Vulcan and commercial Pt/C catalysts respectively.