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Abstract: Platinum nanoparticles were deposited on reduced graphene oxide (rGO) and nitrogen‐doped rGO (rGO−N) by He/H2 plasma jet treatment of H2PtCl6 aqueous solution for electroreduction of oxygen. Physical characterization of the prepared catalysts was performed by scanning electron microscopy, transmission electron microscopy and X‐ray photoelectron spectroscopy. Electrochemical characterization was carried out by cyclic voltammetry and CO‐stripping techniques. The oxygen reduction reaction (ORR) activity of the prepared Pt/rGO and Pt/rGO−N catalyst materials was investigated using the rotating disk electrode method in 0.1 M KOH and 0.05 M H2SO4. In both acidic and alkaline electrolytes, the catalyst materials prepared by the plasma jet method demonstrated superior electrocatalytic properties compared to that of commercial 20 wt% Pt/C catalyst. Specific activity values for the ORR in acid electrolyte were 2‐fold and in alkaline media more than 3‐fold higher than that obtained for commercial Pt/C catalyst. [ABSTRACT FROM AUTHOR]

Dilithium and zinc phthalocyanine derived catalysts supported on multiwalled carbon nanotubes (MWCNTs) have been studied as non-precious metal catalysts for oxygen electroreduction. The electrocatalysts were prepared by simple pyrolysis by varying the pyrolysis temperature and metal phthalocyanine-to-MWCNT ratio. The surface morphology of the catalyst materials was characterized by scanning electron microscopy (SEM) and surface composition by X-ray photoelectron spectroscopy (XPS). The rotating disk electrode (RDE) method was used to determine the electrocatalytic activity of these materials in 0.1 M KOH solution. The oxygen reduction reaction (ORR) activities achieved are comparable to well-studied Fe and Co phthalocyanine based catalysts in alkaline media, showing the great potential of non-redox-active metal phthalocyanine-derived catalysts as cathode materials for metal-air batteries and fuel cells. The number of electrons transferred per O2 molecule was determined by the Koutecky-Levich analysis, which indicated that at high negative potentials the ORR process followed a four-electron pathway. The O2 reduction results obtained in this study show clearly the important role of non-redox-active metal ion in the formation of active sites for ORR on pyrolyzed and carbon supported Li and Zn metallomacrocyclic compounds. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene oxide supported silver nanoparticles (Ag/NGO) have been synthesised using three different methods. The prepared catalysts were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemically tested for oxygen reduction reaction (ORR) in alkaline solution. The Ag/NGO catalysts prepared by borohydride reduction showed the least degree of nanoparticle agglomeration and the material which was prepared using ascorbic acid yielded the biggest Ag particles. XPS revealed that the nitrogen to carbon atomic ratio was about 0.07 and EDS mapping showed that nitrogen was uniformly distributed over the graphene. The ORR on all the Ag/NGO catalysts proceeded via 4-electron pathway yielding water while on the support material, N-doped graphene oxide, the number of electrons transferred per O 2 molecule was lower than four. The mass activity of all Ag/NGO catalysts was determined to be at least twice higher than that of NGO. [ABSTRACT FROM AUTHOR]

In this work the electrocatalysis of oxygen reduction on iron and cobalt phthalocyanine modified reduced graphene oxide/multi-walled carbon nanotube (rGO/MWCNT) composite catalyst has been investigated. Modification of the carbon support was achieved by pyrolysing the mixture of rGO/MWCNT in the presence of metallophthalocyanine compounds at 800 °C. The surface morphology, graphitisation and surface composition of the catalyst materials were characterised by transmission electron microscopy (TEM), scanning electron microscopy (SEM), micro-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The oxygen reduction reaction (ORR) was studied in 0.1 M KOH and 0.5 M H 2 SO 4 solutions on glassy carbon electrodes modified with MN 4 -macrocycle/rGO/MWCNT catalysts employing the rotating disk electrode (RDE) method. The RDE results show that both iron and cobalt phthalocyanine modified rGO/MWCNT electrocatalysts are highly active for ORR in alkaline solution while in acid media these materials exhibit only modest ORR activity. [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]