Electrocatalytic Activity toward Oxygen Reduction of RuS_xN_yCatalysts Supported on Different Nanostructured Carbon Carriers

Abstract

Ruthenium admixed or nanoparticles modified with mixed selenium and nitrogen overlayers (RuSe x N y ) were fabricated onto different carbon nanostructured supports (that include multiwalled carbon nanotubes, Vulcan and Norit) under analogous experimental conditions. It is apparent from X-ray measurements that both Vulcan and Norit supported RuSe x N y crystallites are characterized by the same type of crystallographic phases. Important parameters that influence electrocatalytic activity include the nature of functionalization of carbon support, in addition to its active surface area and morphology that affect distribution and size of active RuSe x N y centers. Despite the same loading of ruthenium (40 μg cm −2 ), diameters of RuSe x N y nanoparticles have somewhat differed and ranged from 2 to 6 nm, as it has been evident from transmission electron microscopy measurements. The systems have been evaluated with respect to oxygen reduction reaction in acid (0.5 M H 2 SO 4 ) medium using rotating ring disk voltammetry and impedance spectroscopy. Having in mind such parameters as the half-wave reduction potential, the electroreduction current density, the heterogenous rate constant, the percent formation of the hydrogen peroxide undesirable intermediate as well as the overall charge transfer resistance appearing during oxygen reduction, the RuSe x N y -based system utilizing functionalized Vulcan is characterized by the highest electrocatalytic activity.The unique textural and electronic properties of carbon materials have been explored with respect to the development of supports for catalytic systems, particularly of interest to the technology of low temperature of fuel cells. 1,2 Utilization of a carbon support allows better distribution of metal centers and leads to increase the electrochemically active area of the catalytic system. Physical properties of carbon supports influence electrochemical activity of dispersed metal nanoparticles. 3,4 Further, when the metal nanoparticles diameter decrease the electrochemically active area increase. 5 Among important features are good electrical conductivity, mechanical rigidity and chemical inertness of carbon supporrts. The porosity factor, which is determined by morphology of the catalyst support, is essential to provide efficient mass transport to the active centers. Uniform dispersion of metal centers and application of carbon supports of high surface area tend to facilitate transport of reactants (fuels). Activity of catalytic systems is also dependent on the nature of interactions between the support and catalytic centers that affect electronic properties of metal nanoparticles, their shape and, indirectly, the number of reactive sites. 6-8 Another important factor is the carbon support corrosion resistance which becomes truly problematic during long-term operation of catalytic systems particularly at temperatures higher than 100 • C. 9,10 In the present work, we comment on the importance of functionalization of three different carbon supports with respect to activit...

Titanium Dioxide as a Catalyst Support in Heterogeneous Catalysis

“…TiO 2 is an interesting material to evaluate as a heterogeneous catalyst support for electrochemical applications, not only because of its high stability cathode potentials in acidic and hydrous environment [19, 34], but also because of the recent reports introducing Ti-containing material into the electrodes [118, 142]. Substoichiometric Ti n O 2 n −2 has been studied and performs well as a catalyst support in cathodes [90, 126].…”

“…Thus, the selection on support heterogeneous catalyst must retain its specific properties, such as porosity, surface area, dispersion, selectivity, and activity [19–21]. The morphology and pores size of the selected support materials play an important role in enhancing the heterogeneous catalyst's stability and performance [20].…”

“…According to the literature, the support of the heterogeneous catalyst can be alumina [22], zeolites [23], carbon nanofibers [19], active carbon [17], and metal oxides [13], such as TiO 2 , La 2 O 3 , CeO 2 , MnO 2 , and ZrO 2 . TiO 2 is a recognized heterogeneous catalyst support that is broadly utilized in fuel processing due to its tunable porous surface and distribution, high thermal stability, and mechanical strength [24, 25].…”

Enhancement of Electrocatalytic Activity of Novel Ruthenium Based Nanocatalyst Supported on Nitrogen Doped Carbons for Oxygen Reduction

“…2 A) powders appear at the same 2θ values indicating the existence of the same crystallographic phases in both materials, however, broader peaks observed for RuSe x N y /CoFeEDA/Norit provide about smaller size of produced crystallites. The location of the reflections reveals of co-existence in particle two phase: RuSe 2 and RuN x (growing in (200) orientation) phase (7). A slight shift of the peaks originating from both of these phase for the RuSe x N y nanoparticles fabricated on the nitrogen doped carbons indicates about increase of interlayer spacing within those phases.…”

“…The actual RRDE voltammograms were recorded at 5 mV s -1 at 1300. The heterogenous rate constants for oxygen reduction at those systems were estimated using the methodology described in details in our previous reports (6,7).…”