Binder-free Li-O2 battery cathodes using Ni- and PtRu-coated vertically aligned carbon nanofibers as electrocatalysts for enhanced stability

The development of an ideal cathode for Li-O2 battery (LOB) has been a great challenge in achieving high discharge capacity, enhanced stability, and longevity. The formation of undesired and irreversible discharge products on the surface of current cathode materials limit the life span of the LOB. In this study, we report the systematic electrochemical study to compare the performance of LOB employing a unique graphitic nanostructured carbon architecture, i.e., vertically aligned carbon nanofiber (VACNF) arrays, as the cathode materials. Transition metal (Ni) and noble metal alloy (PtRu) are further deposited on the VACNF array as electrocatalysts to improve the discharge/charge processes at the cathode. The structure of as-prepared electrodes was examined with the field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). The LOB with VACNF-Ni electrode delivered the highest specific and areal discharge capacities (14.92 Ah·g−1, 4.32 mAh·cm−2) at 0.1 mA·cm−2 current density as compared with VACNF-PtRu (9.07 Ah·g−1, 2.62 mAh·cm−2), bare VACNF (5.55 Ah·g−1, 1.60 mAh·cm−2) and commercial Vulcan XC (3.83 Ah·g−1, 1.91 mAh·cm−2). Cycling stability tests revealed the superior performance of VACNF-PtRu with 27 cycles as compared with VACNF-Ni (13 cycles), VACNF (8 cycles), and Vulcan XC (3 cycles). The superior cycling stability of VACNF-PtRu can be attributed to its ability to suppress the formation of Li2CO3 during the discharge cycle, as elucidated by XPS analysis of discharged samples. We also investigated the impact of carbon cloth and carbon fiber as cathode electrode substrate on the performance of LOB

Platinum Deposited Nitrogen-Doped Vertically Aligned Carbon Nanofibers as Methanol Tolerant Catalyst for Oxygen Reduction Reaction with Improved Durability

Nitrogen doping in carbon materials can modify the employed carbon material’s electronic and structural properties, which helps in creating a stronger metal-support interaction. In this study, the role of nitrogen doping in improving the durability of Pt catalysts supported on a three-dimensional vertically aligned carbon nanofiber (VACNF) array towards oxygen reduction reaction (ORR) was explored. The nitrogen moieties present in the N-VACNF enhanced the metal-support interaction and contributed to a reduction in the Pt particle size from 3.1 nm to 2.3 nm. The Pt/N-VACNF catalyst showed better durability when compared to Pt/VACNF and Pt/C catalysts with similar Pt loading. DFT calculations validated the increase in the durability of the Pt NPs with an increase in pyridinic N and corroborated the molecular ORR pathway for Pt/N-VACNF. Moreover, the Pt/N-VACNF catalyst was found to have excellent tolerance towards methanol crossover

Platinum Deposited Nitrogen-Doped Vertically Aligned Carbon Nanofibers as Methanol Tolerant Catalyst for Oxygen Reduction Reaction with Improved Durability

Nitrogen doping in carbon materials can modify the employed carbon material’s electronic and structural properties, which helps in creating a stronger metal-support interaction. In this study, the role of nitrogen doping in improving the durability of Pt catalysts supported on a three-dimensional vertically aligned carbon nanofiber (VACNF) array towards oxygen reduction reaction (ORR) was explored. The nitrogen moieties present in the N-VACNF enhanced the metal-support interaction and contributed to a reduction in the Pt particle size from 3.1 nm to 2.3 nm. The Pt/N-VACNF catalyst showed better durability when compared to Pt/VACNF and Pt/C catalysts with similar Pt loading. DFT calculations validated the increase in the durability of the Pt NPs with an increase in pyridinic N and corroborated the molecular ORR pathway for Pt/N-VACNF. Moreover, the Pt/N-VACNF catalyst was found to have excellent tolerance towards methanol crossover

Surface photovoltage properties and photocatalytic activities of nanocrystalline CoFe2O4 particles with porous superstructure fabricated by a modified chemical coprecipitation method

In this study, nanocrystalline CoFe2O4 particles with porous timber-like superstructure were synthesized by a modified chemical co-precipitation route with calcination temperatures of 573, 673, 773, 873, and 973 K, respectively. The structural properties of the samples were systematically investigated by X-ray powder diffraction, scanning electronic microscopy, energy-dispersive X-ray spectra, UV-Vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage (SPV) measurement. The photocatalytic performances of the CoFe 2O4 samples were comparatively studied by the degradation of 4-chlorophenol under Xe lamp irradiation. The results indicated that the sample calcined at 673 K exhibited the highest photocatalytic efficiency among the five samples. © Springer Science+Business Media B.V. 2010