16 research outputs found
Electrochemical oxidation of methanol on Pt/(RuxSn1-x)O2 nanocatalyst
The Ru-doped SnO2 powder, (RuxSn1-x)O2, with the Sn:Ru atomic ratio of 9:1
was synthesized and used as a support for Pt nanoparticles (30 mass%
loading). The (RuxSn1-x)O2 support and Pt/(RuxSn1-x)O2 catalyst were
characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and
transmission electron microscopy (TEM). (RuxSn1-x)O2 was found to be
two-phase material consisting of probably solid solution of RuO2 in SnO2 and
pure RuO2. The average Pt particle size determined by TEM was 5.3 nm. Cyclic
voltammetry of Pt/(RuxSn1-x)O2 indicated good conductivity of the sup-port
and displayed usual features of Pt. The results of the electrochemical
oxidation of COads and methanol on Pt/(RuxSn1-x)O2 were compared with those
on commercial Pt/C and PtRu/C catalysts. Oxidation of COads on
Pt/(RuxSn1-x)O2 starts at less positive potentials than on PtRu/C and Pt/C.
Potentiodynamic polarization curves and chronoamperometric curves of methanol
oxidation indicated higher initial activity of Pt/(RuxSn1-x)O2 catalyst
compared to PtRu/C, but also a greater loss in the current density over time.
Potentiodynamic stability test of the catalysts revealed that deactivation of
the Pt/(RuxSn1-x)O2 and Pt/C was primarily caused by the poisoning of Pt
surface by the methanol oxidation residues, which mostly occurred during the
first potential cycle. In the case of PtRu/C the poisoning of the surface was
minor and deactivation was caused by the PtRu surface area loss. [Projekat
Ministarstva nauke Republike Srbije, br. ON-172054
Semiconductor Spintronics
Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure
Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices
Electrodeposition and characterization of Fe–Mo alloys as cathodes
for hydrogen evolution in the process of chlorate productio
Electrodeposition and characterization of Fe-Mo alloys as cathodes for hydrogen evolution in the process of chlorate production (vol 70, pg 879, 2005)
Fe-Mo alloy coatings as cathodes in chlorate production process
The aim of this study was to gain a better understanding of the feasibility
of partial replacement of dichromate, Cr(VI), with phosphate buffer, focusing
on the cathode reaction selectivity for hydrogen evolution on mild steel and
Fe-Mo cathodes in undivided cell for chlorate production. To evaluate the
ability of phosphate and Cr(VI) additions to hinder hypochlorite and chlorate
reduction, overall current efficiency (CE) measurements in laboratory cell
for chlorate production on stationary electrodes were performed. The
concentration of hypochlorite was determined by a conventional potentiometric
titration method using 0.01 mol dm-3 As2O3 solution as a titrant. The
chlorate concentration was determined by excess of 1.0 mol dm-3 As2O3
solution and excess of arsenic oxide was titrated with 0.1 mol dm-3 KBrO3
solution in a strong acidic solution. Cathodic hypochlorite and chlorate
reduction were suppressed efficiently by addition of 3 g dm-3 dichromate at
both cathodes, except that Fe-Mo cathode exhibited higher catalytic activity
for hydrogen evolution reaction (HER). The overvoltage for the HER was around
0.17 V lower on Fe-Mo cathode than on mild steel at the current density of 3
kA m-2. It was found that a dichromate content as low as 0.1 g dm-3 is
sufficient for complete suppression of cathodic hypochlorite and chlorate
reduction onto Fe-Mo catalyst in phosphate buffering system (3 g dm-3 Na2HPO4
+ NaH2PO4). The overall current efficiency was practically the same as in the
case of the presence of 3 g dm-3 dichromate buffer (98 %). However, for the
mild steel cathode, the overall current efficiency for the chlorate
production was somewhat lower in the above mentioned mixed phosphate +
dichromate buffering system (95%) than in the pure dichromate buffering
solution (97.5%)
Activation of Osmium by the Surface Effects of Hydrogenated TiO2 Nanotube Arrays for Enhanced Hydrogen Evolution Reaction Performance
Efficient cathodes for the hydrogen evolution reaction (HER) in acidic water electrolysis rely on the use of expensive platinum group metals (PGMs). However, to achieve economically viable operation, both the content of PGMs must be reduced and their intrinsically strong H adsorption mitigated. Herein, we show that the surface effects of hydrogenated TiO2 nanotube (TNT) arrays can make osmium, a so far less-explored PGM, a highly active HER electrocatalyst. These defect-rich TiO2 nanostructures provide an interactive scaffold for the galvanic deposition of Os particles with modulated adsorption properties. Through systematic investigations, we identify the synthesis conditions (OsCl3 concentration/temperature/reaction time) that yield a progressive improvement in Os deposition rate and mass loading, thereby decreasing the HER overpotential. At the same time, the Os particles deposited by this procedure remain mainly sub-nanometric and entirely cover the inner tube walls. An optimally balanced Os@TNT composite prepared at 3 mM/55 °C/30 min exhibits a record low overpotential (η) of 61 mV at a current density of 100 mA cm-2, a high mass activity of 20.8 A mgOs-1 at 80 mV, and a stable performance in an acidic medium. Density functional theory calculations indicate the existence of strong interactions between the hydrogenated TiO2 surface and small Os clusters, which may weaken the Os-H* binding strength and thus boost the intrinsic HER activity of Os centers. The results presented in this study offer new directions for the fabrication of cost-effective PGM-based catalysts and a better understanding of the synergistic electronic interactions at the PGM|TiO2 interface
Activation of Osmium by the Surface Effects of Hydrogenated TiO2 Nanotube Arrays for Enhanced Hydrogen Evolution Reaction Performance
Efficient cathodes for the hydrogen evolution reaction (HER) in acidic
water electrolysis rely on the use of expensive platinum group metals (PGMs). However, to
achieve economically viable operation, both the content of PGMs must be reduced and
their intrinsically strong H adsorption mitigated. Herein, we show that the surface effects of
hydrogenated TiO2 nanotube (TNT) arrays can make osmium, a so far less-explored PGM,
a highly active HER electrocatalyst. These defect-rich TiO2 nanostructures provide an
interactive scaffold for the galvanic deposition of Os particles with modulated adsorption
properties. Through systematic investigations, we identify the synthesis conditions (OsCl3
concentration/temperature/reaction time) that yield a progressive improvement in Os
deposition rate and mass loading, thereby decreasing the HER overpotential. At the same
time, the Os particles deposited by this procedure remain mainly sub-nanometric and
entirely cover the inner tube walls. An optimally balanced Os@TNT composite prepared at
3 mM/55 °C/30 min exhibits a record low overpotential (η) of 61 mV at a current density
of 100 mA cm−2, a high mass activity of 20.8 A mgOs
−1 at 80 mV, and a stable performance in an acidic medium. Density functional
theory calculations indicate the existence of strong interactions between the hydrogenated TiO2 surface and small Os clusters, which
may weaken the Os−H* binding strength and thus boost the intrinsic HER activity of Os centers. The results presented in this study
offer new directions for the fabrication of cost-effective PGM-based catalysts and a better understanding of the synergistic electronic
interactions at the PGM|TiO2 interface