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The development of efficient and durable earth-abundant electrocatalysts for the oxygen reduction reaction (ORR) is an ongoing challenge. In this work, we directly anchored CoS nanocatalysts (20 wt%) on different supports, namely, carbon nanotubes (CNTs) and reduced graphene oxide by a single-pot hydrothermal route. The developed synthesis processes enabled us to alter the composite nature of CoS by changing the sulfur precursor used. The corresponding electrocatalytic performance of these composite catalysts toward the ORR was studied in alkaline medium. The increase in the effective electrode surface area that accompanies the CoS nanocomposite substantially boosts its ORR catalytic performance. The CoS-CNT-Cy hybrid material shows an onset potential of 0.85 V, which is 60–200 mV less negative than that of other catalysts tested. The catalytic current density achieved with the hybrid material at 0.2 mg cm −2 is comparable with that of commercial Pt/C (20%). The synergistic effect of CNTs and CoS enhances the overall performance of the hybrid catalyst. Extension of this nanocomposite strategy to other earth-abundant materials could similarly enable inexpensive electrocatalysts that lack the high intrinsic activity of the noble metals. [ABSTRACT FROM AUTHOR]

In this work, three kinds of α-MnO 2 nano shapes, namely, nano-wires, nano-tubes and nano-particles have been prepared with a fine control over α-crystallographic form by employing hydrothermal procedure. The materials have been thoroughly characterized by X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) spectrometry, field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The MnO 2 nano shapes are used as a model system for examining the shape-influenced bi-functional electrocatalytic activity towards oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline medium. The bi-functional role has been investigated by cyclic voltammetry and linear sweep voltammetry with rotating ring disc electrode (RRDE) techniques. It is found that α-MnO 2 nano-wires possess enhanced electrocatalytic activity compared to other two shapes namely nano-tubes and nano-particles despite the nano-tubes having a much higher specific surface area. The insight of bi-functional electrocatalytic activity is analysed in terms of catalyst surface with the help of first principles density functional theory (DFT) calculations based on the fact of surface energies and adsorption of water on the surface for a facile reaction. [ABSTRACT FROM AUTHOR]

Abstract: The effect of chemical pre-treatment of the carbon support used for deposition of Pt nano-particles is reported. Data on particle size, distribution and their electocatalytic activity toward hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) are reported. Vulcan XC-72R carbon was pre-treated with 5% HNO3, 0.07 M H3PO4, 0.2 M KOH and 10% H2O2. The properties of carbon supports were studied by N2 adsorption and X-ray photoelectron spectroscopy (XPS). Chemical reduction with ethylene glycol (EG) was used to synthesize Pt on carbon supports and the differences in catalyst morphology were characterized using CO chemisorption, X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. The electrocatalytic activity of Pt/C catalysts toward HOR and ORR was examined by cyclic voltammetry (CV) on a rotating ring-disk electrode (RRDE) and compared with E-Tek Pt/C. The ORR was predominantly involved via four-electron process with the first electron transfer being the rate-determining step. However, the specific activity and mass activity were greatly influenced by the pre-treatment employed. [Copyright &y& Elsevier]