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The electrochemical reduction of oxygen on Pd nanoparticle-decorated nitrogen-doped graphene (Pd/NG) catalyst has been investigated in acid and alkaline solutions using the rotating disk electrode (RDE) method. The Pd/NG nanocomposites were prepared by NaBH4reduction. The surface characterisation of Pd/NG composites was performed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed the uniform distribution of Pd nanoparticles over the N-doped graphene nanosheets. The RDE results indicated that Pd/NG catalysts possess a high electrocatalytic activity towards the oxygen reduction reaction (ORR). The prepared materials catalyse a 4-electron reduction of oxygen. The Tafel behaviour of O2reduction on Pd/NG catalysts was similar to that of bare Pd. The Pd/NG composite showed excellent ORR performance in alkaline media and is a promising material to be used as a cathode catalyst for alkaline membrane fuel cells. [ABSTRACT FROM AUTHOR]

This work focuses on investigating the electrografting of chemical vapour deposition (CVD) graphene electrodes grown onto Ni foil (Ni/Gra) with different diazonium salts (including azobenzene diazonium tetrafluoroborate, Fast Garnet GBC sulphate salt, Fast Black K salt, 4-bromobenzene diazonium tetrafluoroborate and 4-nitrobenzenediazonium tetrafluoroborate). Various grafting conditions (e.g. “normal” electrografting in the narrow potential range and redox grafting in the wider potential range) were used. The electrochemical grafting behaviour was similar for all diazonium compounds used, except for the 4-nitrobenzenediazonium tetrafluoroborate when redox grafting was applied. The X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectroscopy results confirmed the presence of the corresponding aryl layers on Ni/Gra surfaces. The formation of multilayers on Ni/Gra substrates was in evidence since the thickness of different aryl layers varied from few to 30 nm depending on the modification procedures as well as the diazonium compounds used and the XPS analysis revealed a peak at about 400 eV for all aryl-modified Ni/Gra samples suggesting the multilayer formation also through azo linkages. [ABSTRACT FROM AUTHOR]