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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]

Abstract: For the first time, the oxygen reduction reaction (ORR) is studied on pyrolysed electrospun multi-walled carbon nanotube (MWCNT) and styrene-acrylonitrile (SAN) composite fibre catalysts in alkaline medium. Scanning electron microscopy images revealed that the prepared catalysts mainly consist of MWCNTs, while nitrogen doping of the catalysts is confirmed by X-ray photoelectron spectroscopy. This indicates that SAN can be used as a nitrogen precursor. The ORR studies carried out by rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods showed that the prepared catalysts were considerably more active towards the ORR than the pristine MWCNTs.Graphical Abstract: [ABSTRACT FROM AUTHOR]

The aim of this study is to compare the electrochemical behaviour of graphene-based materials of different origin, e.g., commercially available graphene nanosheets from two producers and reduced graphene oxide (rGO) towards the oxygen reduction reaction (ORR) using linear sweep voltammetry, rotating disc electrode and rotating ring-disc electrode methods. We also investigate the effect of catalyst ink preparation using two different solvents (2-propanol containing OH- ionomer or N,N-dimethylformamide) on the ORR. The graphene-based materials are characterised by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Clearly, the catalytic effect depends on the origin of graphene material and, interestingly, the electrocatalytic activity of the catalyst material for ORR is lower when using the OH- ionomer in electrode modification. The graphene electrodes fabricated with commercial graphene show better ORR performance than rGO in alkaline solution. [ABSTRACT FROM AUTHOR]

Abstract: The oxygen reduction reaction has been investigated on double-walled carbon nanotube (DWCNT) modified glassy carbon (GC) electrodes in acid and alkaline media using the rotating disk electrode (RDE) method. The surface morphology and composition of DWCNT samples was examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Aqueous suspensions of DWCNTs were prepared using Nafion and non-ionic surfactant Triton X-100 as dispersing agents. The RDE results indicated that the DWCNT modified GC electrodes are active catalysts for oxygen reduction in alkaline solution. In acid media DWCNT/GC electrodes possess poor electrocatalytic properties for O2 reduction which indicates lack of metal catalyst impurities in the DWCNT material studied. The oxygen reduction behaviour of DWCNTs was similar to that of multi-walled carbon nanotubes (MWCNTs) observed in our previous studies. [Copyright &y& Elsevier]

Abstract: In this paper, the electrochemical reduction of oxygen has been studied on gold nanoparticle/multi-walled carbon nanotube (AuNP/MWCNT) modified glassy carbon (GC) electrodes in 0.5M H2SO4 using the rotating disk electrode (RDE) method. The AuNP/MWCNT catalysts were prepared by chemical deposition of AuNPs onto MWCNTs spontaneously grafted with 4-nitrophenyl groups. The composite electrode was characterised by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The oxygen reduction behaviour of these electrodes was compared with that of a bulk gold electrode. The AuNP/MWCNT catalyst showed a pronounced electrocatalytic activity towards O2 reduction in acid media. The half-wave potential of O2 reduction on the AuNP/MWCNT catalyst shifted ca 80mV to more positive potentials as compared to that of a polished Au electrode. The kinetic parameters of oxygen reduction were determined and the specific activity of the hybrid electrode was slightly higher than that of the bulk Au electrode. [Copyright &y& Elsevier]

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O 2 reduction was 0.184 mA cm −2 , which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm −2 ) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles (NPs) were photo-deposited on SnO 2 -C nanocomposites prepared by sol-gel method. Surface morphology of the prepared materials, examined by scanning electron microscopy (SEM) and transmission electron microscopy, confirmed selective deposition of Pt NPs on SnO 2 nanoclusters formed on carbon surface. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analysis, cyclic voltammetry (CV) and CO stripping experiments revealed modification of the electronic properties of the Pt NPs photo-deposited on the oxide-carbon composite in comparison to Pt/C prepared by the carbonyl chemical route. Rietveld refinement was employed to identify existing phases of catalysts and to determine the crystallite size. Micro-strain and intrinsic stacking fault increased and decreased, respectively, as a function of crystallite size. Pt loadings were determined by inductively coupled plasma mass spectrometry (ICP-MS). The oxygen reduction reaction (ORR) activity of the electrocatalysts was investigated in acid media using the rotating disk electrode (RDE) system. Accelerated durability test (ADT) results showed that photo-deposited Pt nanoparticles onto SnO 2 -C nanocomposite are more durable than those chemically deposited on carbon. • Pt/SnO 2 -C composite electrocatalysts were prepared by photo-deposition. • For comparison, platinum nanoparticles were chemically deposited on carbon. • Metal-support interaction was studied by physical and electrochemical characterization. • Pt/SnO 2 -C catalysts showed high oxygen reduction activity in acid media. • Durability of the Pt/SnO 2 -C catalyst was superior in comparison with Pt/C. [ABSTRACT FROM AUTHOR]

Acid-treated multi-walled carbon nanotubes (MWCNTs) were decorated with TiO 2 using the atomic layer deposition (ALD) technique followed by uniform distribution of platinum nanoparticles (PtNPs) through magnetron sputtering. Surface analyses were performed by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical decontamination and characterization of the Pt-TiO 2 /MWCNT electrodes were carried out by CO stripping followed by cyclic voltammetry in acid media. The oxygen reduction reaction (ORR) was studied in O 2 -saturated 0.05 M H 2 SO 4 solution using the rotating disk electrode (RDE) method. Durability of the prepared catalysts was examined by repetitive potential cycling. Electrochemical data obtained was analyzed and compared to that of the commercial Pt/C catalyst. It was revealed that the Pt-TiO 2 /MWCNT catalysts possess higher ORR activity and better durability as compared to that of the commercial Pt/C. [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]

Nitrogen-doped carbon aerogels containing transition metals have been used as non-precious metal catalysts for oxygen reduction reaction (ORR). The electrocatalysts were prepared by sol–gel polymerisation of organic precursors, followed by insertion of Co or Fe by ion exchange and subsequent carbonisation. The resulting materials were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical testing of the catalysts by thin-film rotating disk and ring-disk electrode technique revealed their high activity and stability in alkaline solution. Cobalt-containing aerogel showed slightly better performance than iron-containing material and the aerogel not containing transition metals was considerably less active. The Koutecky–Levich analysis indicated nearly four-electron reduction of O 2 on metal-containing nitrogen-doped carbon aerogels. The non-precious metal catalysts studied could be used as cathode materials for alkaline membrane fuel cells. [ABSTRACT FROM AUTHOR]

Highlights: [•] O2 reduction was studied on GC electrodes modified with thick anthraquinone films. [•] AQ groups were electrografted onto GC surface using the diazonium reduction method. [•] The XPS analysis confirmed the presence of azo linkages within the AQ film. [•] The O2 reduction activity of the AQ films of various thickness was rather similar. [•] Two-electron reduction of oxygen to hydrogen peroxide was in evidence. [Copyright &y& Elsevier]

Abstract: The oxygen reduction reaction has been investigated on acid-treated single-walled (SWCNT) and multi-walled carbon nanotubes (MWCNT) modified glassy carbon (GC) electrodes in acid media using the rotating disk electrode (RDE) method. Different acids were used for the carbon nanotube (CNT) purification. A systematic study was carried out to elucidate whether the metal catalyst impurities of CNTs play a role in the electroreduction of oxygen on the CNT modified GC electrodes. The surface morphology of the carbon nanotube samples was examined by transmission electron microscopy and the concentration of metal catalysts in the CNT materials was determined by energy dispersive X-ray spectroscopy. The acid-treated MWCNTs were also characterised by Raman and X-ray photoelectron spectroscopies. Aqueous suspensions of SWCNTs and MWCNTs used for GC surface modification were prepared in the presence of Nafion. The RDE results indicated that the acid-treated CNT modified GC electrodes are less active catalysts for oxygen reduction than as-received CNTs which could be explained by the absence of metal catalysts on the surface of purified CNTs. [Copyright &y& Elsevier]

Abstract: The electrochemical reduction of oxygen was studied on vacuum evaporated thin Pt films (0.25–20nm thick) on polycrystalline Au substrate (Pt/Au) in 0.1M HClO4 and 0.05M H2SO4 solutions using the rotating disk electrode (RDE) method. The surface morphology of Pt films was examined by scanning tunnelling microscopy (STM). The O2 reduction specific activity of Pt films increased with increasing the film thickness in HClO4, but was lower than that of bulk Pt even for the thickest films. In H2SO4, the specific activity showed no significant dependence on the platinum loading and was lower than in HClO4. The Tafel slope values characteristic to polycrystalline Pt (−120mVdec−1 and −60mVdec−1) were found for all electrodes. The RRDE studies of 0.5nm Pt/Au electrode revealed that O2 reduction predominantly proceeds through 4e− pathway and H2O2 is produced in low quantities. [Copyright &y& Elsevier]