Continuously-variable survival exponent for random walks with movable partial reflectors

We study a one-dimensional lattice random walk with an absorbing boundary at the origin and a movable partial reflector. On encountering the reflector, at site x, the walker is reflected (with probability r) to x-1 and the reflector is simultaneously pushed to x+1. Iteration of the transition matrix, and asymptotic analysis of the probability generating function show that the critical exponent delta governing the survival probability varies continuously between 1/2 and 1 as r varies between 0 and 1. Our study suggests a mechanism for nonuniversal kinetic critical behavior, observed in models with an infinite number of absorbing configurations.Comment: 5 pages, 3 figure

Electrodeposition and characterization of Fe–Mo alloys as cathodes for hydrogen evolution in the process of chlorate

Fe–Mo alloys were electrodeposited from a pyrophosphate bath using a single diode rectified AC current. Their composition and morphology were investigated by SEM, optical microscopy and EDS, in order to determine the influence of the deposition conditions on the morphology and composition of these alloys. It was shown that the electrodeposition parameters, such as: chemical bath composition and current density, influenced both the composition of the Fe–Mo alloys and the current efficiency for their deposition, while the micro and macro-morphology did not change significantly with changing conditions of alloy electrodeposition. It was found that the electrodeposited Fe–Mo alloys possessed a 0.15 V to 0.30 V lower overvoltage than mild steel for hydrogen evolution in an electrolyte commonly used in commercial chlorate production, depending on the alloy composition, i.e., the conditions of alloy electrodeposition

Synthesis and Characterization of Pt Catalysts on SnO2 Based Supports for Oxygen Reduction Reaction

The oxygen reduction reaction was studied at Pt nanocatalysts on two different tin oxide based supports, Sb-SnO2 and Ru-SnO2, in acid solution. Tin oxide based supports were synthesized by hydrazine reduction method. Physical characterization of the supports was performed by BET, X-ray diffraction and TEM techniques. SnO2 belonging peaks were detected in Sb-SnO2 powder, while Ru-SnO2 XRD diffraction patterns contained peaks of RuO2 and SnO2. The average crystallite sizes, determined by Scherrer equation, were 3 nm and 4 nm for Sb-SnO2 and Ru-SnO2, respectively. Pt catalysts on Sb-SnO2 and Ru-SnO2 supports were synthesized by borohydride reduction method. TEM analysis revealed homogeneous particle size distribution, with average particle size of 2.9 and 5.4 nm, for Sb-SnO2 and Ru-SnO2, respectively. Electrocatalytic activity and stability of these catalysts for oxygen reduction were studied by cyclic voltammetry and linear sweep voltammetry at rotating disk electrode (RDE). Pt catalysts on Sb and Ru doped SnO2 support exhibited catalytic activities comparable to Pt on commercial carbon based support. Stability tests were also performed. Determined small loss of electrochemical active surface area of the Pt catalyst on Sb doped tin oxide support, after repetitive cycling, indicated high stability and durability of this cathode for-prospective fuel cells application. (C) 2013 The Electrochemical Society. All rights reserved

Oxygen reduction at platinum nanoparticles supported on carbon cryogel in alkaline solution

The oxygen reduction reaction was investigated in 0.1 M NaOH solution, on a porous coated electrode formed of Pt particles supported on carbon cryogel. The Pt/C catalyst was characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry techniques. The results demonstrated a successful reduction of Pt to metallic form and homogenous Pt particle size distribution with a mean particle size of about 2.7 nm. The ORR kinetics was investigated by linear sweep polarization at a rotating disc electrode. The results showed the existence of two E - log j regions, usually referred to polycrystalline Pt in acid and alkaline solution. At low Current densities (led), the Tafel slope was found to be close to -2.3RT/F, while at high current densities (bed) it was found to be close to -2x2.3RT/F. It is proposed that the main path in the ORR mechanism on Pt particles was the direct four-electron process, with the transfer of the first electron as the rate determining step. If the activities are expressed through the specific current densities, a small enhancement of the catalytic activity for Pt/C was observed compared to that of polycrystalline Pt. The effect of the Pt particle size on the electrocatalysis of oxygen reduction was ascribed to the predominant (111) facets of the platinum crystallites

Novel Pt catalyst on ruthenium doped TiO2 support for oxygen reduction reaction

Ruthenium doped titanium oxide support was synthesized. The support was characterized by BET (Brunauer, Emmett, Teller) and X-ray diffraction techniques (XRD). Determined specific surface area was 41 m(2) g(-1). XRD revealed presence mainly TiO2 anatase phase and some peaks belonging to rutile phase. No Ru compounds have been detected. Platinum based catalyst on this support was prepared by borohydride reduction method. The catalyst was characterized by scanning transmission electron microscopy (STEM, HAADF) and electron energy loss spectroscopy (EELS). Homogenous Pt particle distribution over the support, with average Pt nanoparticle diameter of 3 nm was found. This novel catalyst was tested for oxygen reduction in acid solution. It exhibited remarkable higher catalytic activity in comparison with Pt/C, as well as with Pt nanocatalysts at titanium oxide based supports, reported in literature. (C) 2013 Elsevier B.V. All rights reserved