Carbon-Supported Palladium–Polypyrrole Nanocomposite for Oxygen Reduction and Its Tolerance to Methanol

Carbon-supported palladium–polypyrrole Pd–PPy/C nanocomposite was synthesized by oxidative polymerization of pyrrole and reduction of palladium(II) precursor salt in the presence of Vulcan XC-72R. The Pd–PPy/C composites were characterized by X-ray diffraction (XRD), Fourier transform IR, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. The XRD analysis of Pd–PPy/C shows the formation of the face-centered cubic structure of Pd particles and the mean particle size calculated from TEM was 5.3 2.0 nm. The electrochemical stability of Pd–PPy/C was examined by cyclic voltammetry in an acid solution. The thermal stability and Pd loading in the composite was assessed using TGA. The introduction of Pd in the conducting PPy/C matrix gives better catalytic activity toward oxygen reduction with resistance to methanol oxidation. This was further elucidated by the XPS analysis showing d-band vacancy that is attributed to metal–polymer interaction. From the polarization studies, it is observed that even in the presence of methanol there is no significant cathodic shift in the half-wave potential, revealing that Pd–PPy/C is tolerant to methanol. Rotating ring disk electrode studies show that there is only a negligible quantity of hydrogen peroxide produced in the potential region where its production is expected to be high. This confirms that Pd–PPy/C catalyzes reduction of oxygen directly to water through a four-electron pathway

Methanol tolerant oxygen-reduction activity of carbon supported platinum–bismuth bimetallic nanoparticles

The oxygen reduction activity and methanol tolerance of Pt–Bi/C electrocatalysts were studied using electrochemical voltammetric techniques including rotating ring-disk electrode. The Pt–Bi/C catalyst was prepared via a polyol method and subjected to heat treatment to increase the degree of alloying. X-ray diffraction studies revealed the unalloyed character of the as-prepared catalyst and alloy formation upon heat treatment. The electrochemical behaviour of both catalysts showed different behaviour in dilute acid electrolytes, namely sulphuric and perchloric acids. In both electrolytes, the oxygen reduction reaction was found to occur via the four-electron process revealing that the mechanism of oxygen reduction is unaltered even in the presence of excess of methanol. Pt–Bi/C catalyst material showed dramatically different properties and reactivity with respect to oxygen reduction activity and methanol tolerance in perchloric and sulphuric acids. The onset potential for oxygen reduction reaction (ORR) significantly shifted by about 100 mV to more negative values and at the same time the current density was significantly enhanced. This type of non-ideal methanol-tolerant behaviour among Pt bimetallics and a ‘‘trade off’’ is common with all the known so-called methanol tolerant combinations of Pt. In general, the Pt–Bi surface appeared to have a negligibly lesser sensitivity towards methanol activity compared to pure platinum

Platinum–tin bimetallic nanoparticles for methanol tolerant oxygen-reduction activity

Carbon-supported Pt–Sn/C bimetallic nanoparticle electrocatalystswere prepared by the simple reduction of the metal precursors using ethylene glycol. The catalysts heat-treated under argon atmosphere to improve alloying of platinum with tin. As-prepared Pt–Sn bimetallic nanoparticles exhibit a single-phase fcc structure of Pt and heat-treatment leading to fcc Pt75Sn25 phase and hexagonal alloy structure of the Pt50Sn50 phase. Transmission electron microscopy image of the as-prepared Pt–Sn/C catalyst reveals a mean particle diameter of ca. 5.8nm with a relatively narrow size distribution and the particle size increased to ca. 20nm when heat-treated at 500 ◦C due to agglomeration. The electrocatalytic activity of oxygen reduction assessed using rotating ring disk electrode technique (hydrodynamic voltammetry) indicated the order of electrocatalytic activity to be: Pt–Sn/C (as-prepared) > Pt–Sn/C (250 ◦C) > Pt–Sn/C (500 ◦C) > Pt–Sn/C (600 ◦C) > Pt–Sn/C (800 ◦C). Kinetic analysis reveals that the oxygen reduction reaction on Pt–Sn/C catalysts follows a four-electron process leading to water. Moreover, the Pt–Sn/C catalyst exhibited much higher methanol tolerance during the oxygen reduction reaction than the Pt/C catalyst, assessing that the present Pt–Sn/Cbimetallic catalystmay function as amethanol-tolerant cathode catalyst in a direct methanol fuel cell

Nitrogen-doped carbon black as methanol tolerant electrocatalyst for oxygen reduction reaction in direct methanol fuel cells

Nitrogen-doped metal free carbon catalysts were prepared via pyrolysis of polyaniline-coated carbon in different ratios with varying nitrogen content. The surface states and surface composition were investigated using XPS (X-ray photoelectron spectroscopy). XPS analysis confirms the presence of pyridinic and pyrollic nitrogen in the carbon network that is responsible for the oxygen reduction activity. The shift in onset potential of oxygen reduction on C:N (1:1) is ∼0.3 V more positive compared to Vulcan carbon, shows improved activity toward oxygen reduction reaction in acidic electrolyte. Hydrodynamic voltammetric studies confirm that the reduction of oxygen follows the 4e− pathway which leads to the formation of wate

Tuning the Anodic and Cathodic Dissolution of Gold by Varying the Surface Roughness

Abstract This work presents the reactivity and dissolution of an as‐polished and electrochemically pre‐treated polycrystalline Au electrode, which is used as a model system. The effect of the electrochemical pre‐treatment in corrosive 0.37 M HCl solutions on the Au surface roughness and dissolution is investigated by varying the number of pre‐treatment steps at 1.16 V against the reversible hydrogen electrode. It is shown that the first 10 s pre‐treatment of the as‐polished Au results in a higher surface roughness and thus higher electrochemically active surface area (ECSA) than that of the as‐polished Au. With the subsequent pre‐treatments, however, the ECSA is gradually decreasing reaching a steady value. The dissolution rate of the pre‐treated Au electrodes upon potential cycling in 0.1 M H2SO4 is determined by in situ inductively coupled plasma mass spectrometry. A non‐linear dependence of Au dissolution amount is found with respect to the number of pre‐treatments. The overall total Au dissolution rate follows a similar trend as ECSA/roughness. However, an important difference in the dissolution behavior is identified with respect to dissolution processes during Au oxidation (anodic dissolution) and Au reduction (cathodic dissolution): the former is more sensitive to the surface roughness. Thus, the ratio between Au anodic and cathodic dissolution amounts decreases substantially with decrease in surface roughness. This finding is explained by the slow and fast dissolution kinetics for anodic and cathodic processes, respectively. Current work further advances our understanding of the complex Au dissolution mechanism