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Formation of the honeycomb-like electrodes of copper by the regime of reversing current (RC) in the second range has been investigated. Morphological and structural characteristics of this electrode type obtained by various parameters of RC regimes were examined by the techniques of scanning electron and optical microscopies, while the amount of hydrogen produced during electrodeposition process was quantified by determination of the average current efficiency for hydrogen evolution reaction. To optimize the process of formation of the honeycomb-like electrodes, the following parameters of square wave RC regimes were analyzed: the cathodic current density, the same anodic to cathodic time ratios but various durations of the cathodic and the anodic pulses, and the various values of the anodic to cathodic time ratios. The minimal amount of hydrogen spent for formation of the honeycomb-like electrodes with maximal number of holes formed from detached hydrogen bubbles is obtained with the anodic to cathodic time ratio of 0.50 and duration of the cathodic and anodic pulses of 2 and 1 s, respectively. To explain formation of the honeycomb-like electrodes of optimal morphological and structural characteristics, the upgraded mathematical model defining the RC regime in the second range was proposed and discussed.

Developing ultraefficient electrocatalytic materials for the hydrogen evolution reaction (HER) with low content of expensive platinum group metals (PGMs) via low-energy-input procedures is the key to the successful commercialization of green water electrolysis technologies for sustainable production of high-purity hydrogen. In this study, we report a facile room-temperature synthesis of ultrafine metallic Ir nanoparticles on conductive, proton-intercalated TiO2 nanotube (H-TNT) arrays via galvanic displacement. A series of experiments demonstrate that a controlled transformation of the H-TNT surface microstructure from neat open-top tubes to disordered nanostripe bundles (“nanograss”) is highly beneficial for providing an abundance of exposed Ir active sites. Consequently, for nanograss-engineered composites, outstanding HER activity metrics are achieved even at very low Ir(III) precursor concentrations. An optimum Ir@TNT cathode loaded with 5.7 μgIr cm−2 exhibits an overpotential of −63 mV at −100 mA cm−2 and a mass activity of 34 A mgIr−1 at −80 mV under acidic conditions, along with excellent catalytic durability and structural integrity. Density functional theory (DFT) simulations reveal that the hydrogen-rich TiO2 surface not only stabilizes the deposited Ir and weakens its H binding strength to a moderate intensity, but also actively takes part in the HER mechanism by refreshing the Ir catalytic sites near the Ir|H–TiO2 interface, thus substantially promoting H2 generation. The comprehensive characterization combined with theory provides an in-depth understanding of the electrocatalytic behavior of H-TNT supported PGM nanoparticles and demonstrates their high potential as competitive electrocatalyst systems for the HER.

The Ag, Pd and AgPd alloys of different morphologies and compositions were electrodeposited onto Au and glassy carbon (GC) disc electrodes from the solution containing 0.001 M PdCl2 þ 0.04 M AgCl þ 0.1 M HCl þ 12 M LiCl under the conditions of non-stationary (RPM ¼ 0, samples AgPd1 and AgPd2) and convective diffusion (RPM ¼ 1000, sample AgPd3). Electrodeposited alloy layers were characterized by the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Oxygen reduction reaction (ORR) was investigated on all coatings in 0.1 M NaOH solution saturated with oxygen. The j-E curves for the ORR were recorded by two proced- ures: (1) samples were cycled with 5 mV s 1 from open circuit potential (OCP) to 0.8 V for Ag and AgPd alloys (or 0.6 V for pure Pd) and back; (2) samples were cycled with 5 mV s 1 from open circuit po- tential to 0.45 V (formation of Ag2O, in the case of Pd formation of PdO and PdO2), from 0.45 V to 0.60 V and back to the OCP. Significant catalytic activity for the Ag and AgPd alloys was detected after cycling electrodes in the potential region of Ag2O formation and reduction. Increase of the catalytic activity for AgPd alloys was, for the first time in the literature, ascribed to the presence of a certain amount of Ag2O which could not be completely reduced during the reverse sweep from 0.45 V to 0.6 V. Catalytic activity of AgPd alloys was found to be closely related to the amount of non-reduced Ag2O (most probably in the form of Ag-hydroxide). In the absence of such treatment, the catalytic activity for the ORR on electro- deposited Ag and AgPd alloy coatings was not detected.

Electrodeposition of copper in the hydrogen co-deposition range by the regime of reversing current (RC) in the second range has been investigated by determination of the average current efficiency for hydrogen evolution reaction and by scanning electron (SEM) and optical (OM) microscopic analysis of the obtained deposits. Keeping the cathodic current density, the cathodic and the anodic pulses constant in all experiments, the anodic current density (ja) values were varied: 40, 80, 160, 240 and 320 mA cm−2. The Cu deposits produced by the RC regimes with different anodic current density values were compared with that obtained in a constant galvanostatic regime (DC) at the current density equal to the cathodic current density in the RC regimes. The honeycomb-like structures were formed in the DC regime and by the RC regimes with ja of 40 and 80 mA cm−2. The hole size in them was in the 60–70 μm range. Due to the decrease of quantity of evolved hydrogen with increasing anodic current density, the larger dish-like holes with dendrites at their bottom and shoulder were formed with ja values of 160, 240 and 320 mA cm−2. The maximum number of holes, and hence, the largest specific surface area of the honeycomb-like electrodes was obtained with ja = 80 mA cm−2, that can be ascribed to a suppression of coalescence of neighboring hydrogen bubbles. Application of the RC regime also led to the increase of uniformity of structures, what is concluded by cross section analysis of the formed honeycomb-like electrodes. For the first time, mechanism of Cu electrodeposition in the hydrogen co-deposition range by the RC regime in the second range was proposed and discussed. This is peer-reviewed version of the article: Journal of Electroanalytical Chemistry, 2019, 833, 401-410, [https://doi.org/10.1016/j.jelechem.2018.12.021] [http://cer.ihtm.bg.ac.rs/handle/123456789/2986]

Two types of iridium oxide films formed at the Ti-2 AlC substrate were investigated: (1) anodically electrodeposited iridium oxide film from the solution based on IrCl(3)xH(2)O; (2) iridium oxide film prepared by cycling thin layer of electrodeposited Ir in the 0.5 M H2SO4 from - 0.25 to 1.20 V. It was shown that during anodic electrodeposition of iridium oxide film (1) coulombic efficiency decreases with increasing anodic potential, being only 3% atE = 0.7 V vs. SCE and 26% atE = 0.62 V vs. SCE. A pair of peaks corresponding to the transition Ir(III)-oxide/Ir(IV)-oxide was present on the CVs recorded in 0.5 M H2SO4. While cycling pure Ir thin layer in the solution of 0.5 M H2SO4 from - 0.25 to 1.20 V (2) up to 100 cycles, typical CV response was characterized with the prepeak and a pair of peaks corresponding to the Ir(III)/Ir(IV)-oxide transition. With the increase of cycles number to 150, additional peak at potential of 1.0 V appeared. This peak was formed on the account of pair of peaks corresponding to the Ir(III)/Ir(IV)-oxide transition. The oxygen evolution reaction (OER) was investigated at both iridium oxide films. It was shown that the Tafel slope for the OER was similar to 40 mV dec(-1)for the first polarization curve, confirming that the rds was a reaction S-OH - gt S-O-ads + H++ e(-). As the number of recorded polarization curves increased, the activity of both types of iridium oxide films decreased, due to dissolution of iridium oxide films at the potentials of the OER. It is shown that anodically electrodeposited iridium oxide film is more active for the OER than that obtained by cycling electrodeposited iridium layer. However, both iridium oxide films exhibited insufficient stability.

Electrodeposited NiSn alloy coatings onto Ni 40 mesh substrate were tested for application as cathodes and anodes in the cell for alkaline water electrolysis in 30 wt% KOH at 80 °C. The “accelerated service life test” (ASLT) was performed for the hydrogen evolution reaction (HER), as well as for the oxygen evolution reaction (OER), and compared to that recorded for the Ni coating ( Ni-dep ) and Ni-mesh for both reactions. The morphology and chemical compositions of the NiSn and Ni coatings were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), while their surface composition was investigated by X-ray photoelectron spectroscopy (XPS) before and after the ASLT for both reactions, respectively. By measuring the potential at j = 0.3 A cm − 2 it was shown that during the ASLT the NiSn alloy coating catalytic activity for the HER decreases (about 24 mV after 25 cycles), while the catalytic activity for the OER increases (about 50 mV after 25 cycles), so that the cell voltage decreases for about 26 mV. The Ni-dep and Ni-mesh electrodes catalytic activity was found to increase for the HER (for about 103 mV), as well as for the OER (for about 52 mV) during the ASLT. Hence, the cell voltage for the Ni-dep and Ni-mesh electrodes decreased from 2.402 V to 2.245 V during the ASLT, while that for the NiSn electrode decreased from 1.967 V to 1.941 V. The cell voltage saving with the NiSn electrodes amounts to about 435 mV before the ASLT and about 304 mV after the ASLT. SEM results showed that no changes in the morphology of as prepared samples could be detected after the ASLTs for both reactions. EDS analysis confirmed that some changes occurred during the ASLT, particularly for the oxygen content in the surface layer. Similar conclusions were made from the XPS analysis.

Noble metal-based materials are inevitable components of cathodes for the hydrogen evolution reaction (HER) in future water electrolysis systems for clean hydrogen fuel production. However, designing active and durable nanostructured catalysts with low amount of costly noble metals is still a great challenge. Herein, we show that Pd nanoparticles (NPs) can be synthesized on the highly developed surface of anodically grown TiO2 nanotube (TNT) arrays by applying a simple galvanic displacement strategy. In a two-step procedure, air-annealed TNT arrays are first cathodically protonated and then partially reoxidized by Pd(II) ions from a PdCl2 solution while providing a scaffold for the metallic Pd deposit. Structural and electrochemical characterizations reveal that the Pd content and the width of the Pd-populated zone of the tube walls are in correlation with the tube length. The Pd@TNT composites display remarkable HER activity in 1 M HClO4 delivering a current density of −10 mA cm−2 at an overpotential of −38 mV and a Tafel slope of only −13 mV/dec. More impressively, the mass and apparent activity of the Pd@TNTs is superior to even commercial Pt/C at higher current densities. The composites also show stable chronopotentiometric response over 25 h and a negligible HER overpotential increase after potential cycling tests. The exceptional performance of the Pd@TNT cathodes is assigned to the unique semiconducting properties of the three-dimensional, interactive TNT supporting structures that, on the one hand, provide abundance of Pd active sites with optimized atomic hydrogen binding energy for the cathodic HER, but on the other hand, prevent anodic degradation of the Pd catalyst.

The AgPd alloys were electrodeposited onto Au and glassy carbon disc electrodes from the solution containing 0.001 mol dm-3 PdCl2 + 0.04 mol dm-3 AgCl + 0.1 mol dm-3 HCl + 12 mol dm-3 LiCl under the non-stationary diffusion (quiescent electrolyte) and convective diffusion (ω = 1000 rpm) to the different amounts of charge and at different current densities. Electrodeposited alloy layers were characterized by the anodic linear sweep voltammetry (ALSV), scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The compositions of the AgPd alloys determined by the EDS were almost identical to the theoretically predicted ones, while the compositions obtained by XPS and ALSV analysis were similar to each other, but different from those obtained by EDS. Deviation from the theoretically predicted values (determined by the ratio jL(Pd)/j(Ag)) was more pronounced at lower current densities and lower charges of AgPd alloys electrodeposition, due to the lower current efficiencies for alloys electrodeposition. The ALSV analysis indicated the presence of Ag and Pd, expressed by two ALSV peaks, and in some cases the presence of the additional peak, which was found to correspond to the dissolution of large AgPd crystals, formed at thicker electrodeposits (higher electrodeposition charge), indicating, for the first time, that besides the phase structure, the morphology of alloy electrodeposit could also influence the shape of the ALSV response. In addition to Ag and Pd, the XPS analysis confirmed the presence of AgCl at the surface of samples electrodeposited to low thicknesses (amounts of charge). [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172054]

Ag-In, Pd-In and Co-In alloy coatings were electrodeposited under galvanostatic conditions from different solutions. The appearance and the composition of coatings were investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The appearance of spatio-temporal structures on the surface of electrodeposited alloy layers is characteristic for all three indium containing alloys. Well-distinguished spirals were detected only at the surfaces of Ag-In and Co-In alloys, while for Pd-In alloy spatio-temporal structures are characterized with the valleys of different shapes surrounded by hills. In the case of Ag-In and Pd-In alloy coatings the cross-section does not show the presence of alloy layers with different composition, due to the fact that spatio-temporal structures are of large dimensions and cannot be seen on the high magnification images of the cross-sections. EDS line scan of the cross-section of Co-In alloy layers indicates the presence of layers with different compositions at high magnification, confirming that spatio-temporal structures are placed not only on the surface, but also in the bulk of the alloy coating.

In spite of the fact that the field of electrochemical science has had a long tradition in Serbia, it wasn’t until the most recent 2020 event that Belgrade was chosen to be a host of the Annual Mee...

Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil microemulsion method and examined for formic acid and methanol oxidation. Prepared catalyst powder was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). These techniques revealed that the catalyst contains rather agglomerated quasi-spherical particles, similar to 4 nm diameter, composed of a solid solution of Pt and Au with only similar to 4 at% of Au. In spite of such low Au content, both onset and peak potentials for CO oxidation are shifted some 150 mV to more positive values in comparison to Pt synthesized in the same manner due to stronger binding of CO as a result of notable electronic effect. It is important that this small quantity of Au also significantly influences oxidation of formic acid promoting direct path and suppressing indirect path in formic acid oxidation in a degree as expected by a much larger quantity of Au. Such improvement could be due exclusively by ensemble effect of high number of small Pt domains which formation could be possible only by very fine dispersion of such low Au quantity. High number of small Pt domains is corroborated by lower activity for methanol oxidation in comparison to Pt catalyst synthesized by the same procedure. These results emphasize the importance of the Au dispersion on the surface of Pt over its quantity in PtAu catalyst with regards to both, the ensemble and the electronic effects. [http://cer.ihtm.bg.ac.rs/handle/123456789/2490]

The hydrogen evolution reaction (HER) was investigated in 0.5 M H2SO4 at thin iridium layers electrodeposited on Ti2AlC substrate. Five samples, varying in thickness from 4.5 nm to 255 nm, were electrodeposited from the solution containing K3IrCl6 + Na2SO4. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were applied for morphology and chemical composition analysis. Metallic iridium was detected by X-ray photoelectron spectroscopy (XPS). The HER was investigated by polarization and electrochemical impedance spectroscopy (EIS) measurements. Polarization curves were characterized with the low Tafel slopes ~ −18 mV dec−1, while at higher current densities increased up to −56 mV dec−1. The overpotential at j = −0.1 A cm−2 was ~45 mV, while at j = −0.01 A cm−2 varied from 25.1 mV to 36.1 mV. These novel catalysts exhibited excellent activity, especially under industrial conditions of hydrogen production (j = −0.3 A cm−2) - the determined overpotentials were between 66 and 69 mV only.

In this manuscript a survey of the contemporary research related to platinum nanocatalysts on metal oxide based supports for low temperature fuel cell applications is presented. Different carbon based supports, used as state of the art materials, are listed and discussed, as well. Although carbon based materials possess many desirable properties, such as high surface area, high conductivity and relatively low cost and easy synthesis, the large scale commercialization is limited by instability under accelerated stability testing, simulating real fuel cell operating conditions. To overcome these disadvantages of carbon supports, different metal oxide based ones have been studied and promising results are referenced. The most often used oxide based supports for low temperature fuel cell applications are presented in this review. Suitable discussion and future research related remarks are given, as well.

The Pd and three AgPd alloy layers (AgPd1, AgPd2 and AgPd3) were electrodeposited onto Au disc electrodes from the solution containing high concentration of chloride ions (>12 M). All coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), anodic linear sweep voltammetry (ALSV), while their surface composition was investigated by X-ray photoelectron spectroscopy (XPS). The AgPd1 and AgPd2 samples were electrodeposited at different constant current densities (−0.178 mA cm−2 and -0.415 mA cm−2 respectively) to the charge of −0.2 C cm−2 (thickness ∼ 0.18 μm) at a stationary disc electrode, while the sample AgPd3 was electrodeposited to the charge of −3.0 C cm−2 (thickness ∼ 2.8 μm) at a constant current density of −7.0 mA cm−2 under the conditions of convective diffusion. Samples AgPd1 and AgPd2 had similar morphologies of low roughness, while the morphology of AgPd3 was characterized by large crystals and higher roughness. The most active and the most poisoning tolerant coatings for ethanol oxidation reaction (EOR) are the AgPd3 and AgPd1 alloy samples, containing 72.6 at.% Ag – 27.4 at.% Pd and 84.7 at.% Ag – 15.2 at.% Pd respectively (XPS analysis). In this study, we demonstrated for the first time that the activity for the EOR at AgPd alloys was closely related to the amount of non-reduced Ag2O (most probably as Ag – hydroxide). Accordingly, all AgPd alloy samples had to be cycled in the potential region of Ag2O formation and reduction before the investigation of the EOR, in order to provide their catalytic activity towards the EOR. © 2018 Hydrogen Energy Publications LLC Supporting information: [https://hdl.handle.net/21.15107/rcub_dais_4082]

A platinum nanocatalyst on Sb doped tin oxide support (Sb-SnO2) was synthesized and characterized as a catalyst for oxygen reduction reaction in 0.1 mol dm(-3) NaOH solution at 25 degrees C. Sb (5%) doped tin oxide support was synthesized by a modified hydrazine reduction procedure. The platinum nanocatalyst (20% Pt) on Sb-SnO2 support was synthesized by a borohydride reduction method. The synthesized support and catalyst were characterized by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) and X-ray diffraction technique (XRD). X-ray photoelectron spectroscopy was applied to characterize the chemical status of elements before and after Pt-treatment. XPS spectra of Sn 3d, Pt 4f, Sb 3d and O 1s revealed that the Pt-deposition on Sb-SnO2 support induced the reduction of the Sn(4+) oxidation state to Sn(2+) and Sn(0) states, while Pt remained in the metallic state and Sb was in the (3+) oxidation state. Homogenous Pt nanoparticle distribution over the support, without pronounced particle agglomeration, was confirmed by HRTEM technique. The average Pt particle size was 2.9 nm. The electrochemically active Pt surface area of the catalyst was determined by the integration of the cyclic voltammetry curve in the potential region of underpotential deposition of hydrogen, after double layer charge correction, taking into account the reference value of 210 mu C cm(-2) for full monolayer coverage. This calculation gave the value of 51 m(2) g(-1). The kinetics of the oxygen reduction reaction with Pt/[Sb-SnO2 catalyst was studied by cyclic voltammetry and linear sweep voltammetry using a rotating gold disc electrode. Two different Tafel slopes were observed: one close to 60 mV dec(-1) in the low current density region, and another at similar to 120 mV dec(-1) in the higher current densities region, as was already referred in previous reports for the oxygen reduction reaction with polycrystalline Pt, as well as with different Pt based nanocatalysts. The specific activities for oxygen reduction, expressed in terms of kinetic current densities per electrochemically Pt active surface area, as well as per mass of Pt loaded, at the constant potential of practical interest (0.85 V and 0.90 V vs. RHE), were compared to a carbon supported (Vulcan XC-72) catalyst. The Pt/[Sb-SnO2 catalyst exhibited similar catalytic activity for oxygen reduction reaction like carbon supported one. The advantages of the carbon free support application in terms of the durability and stability of the catalysts were proved by accelerated stability tests.

© 2017 Elsevier Ltd Tungsten based support was prepared by polycondensation of resorcinol and formaldehyde from ammonium metatungstate, in the presence cetyltrimethylammonium bromide (CTABr) surfactant. Pd nanocatalyst on this support was synthesized by borohydride reduction method. The obtained materials were characterized by High Resolution Transmission Electron Microscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS), X-ray Photoelectron Spectroscopy (XPS) and electrochemical measurements. TEM analysis revealed Pd nanoparticles size in the range of a few nanometers, even the clusters of single Pd atoms. X-Ray Photoelectron Spectroscopy was applied to determine surface composition of the substrates. It was found that tungsten based support consisted of W, WC and WO3species. The presence of metallic palladium – Pd(0) in the Pd/W@WCWO3catalyst was revealed, as well. The catalytic activity and stability for the oxygen reduction were investigated in acid and alkaline solutions, by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. The catalystsʹ activities were compared to the carbon supported Pd nanoparticles (Vulcan XC 72). WC supported Pd nanoparticles have shown high activity and superior stability, comparable even to Pt based catalysts, especially in alkaline electrolytes.

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.

In this manuscript a survey of the contemporary research related to platinum nanocatalysts on metal oxide based supports for low temperature fuel cell applications is presented. Different carbon based supports, used as state of the art materials, are listed and discussed, as well. Although carbon based materials possess many desirable properties, such as high surface area, high conductivity and relatively low cost and easy synthesis, the large scale commercialization is limited by instability under accelerated stability testing, simulating real fuel cell operating conditions. To overcome these disadvantages of carbon supports, different metal oxide based ones have been studied and promising results are referenced. The most often used oxide based supports for low temperature fuel cell applications are presented in this review. Suitable discussion and future research related remarks are given, as well.

Platinum nanocatalysts on two tungsten based supports have been synthesized and characterized as catalysts for oxygen reduction reaction in 0.5 mol dm −3 HClO 4 solution, at 25 °C. Tungsten based support assigned WCctabr has been synthesized by polycondensation of resorcinol and formaldehyde in the presence of CTABr surfactant. Support assigned WC WO 3 was synthesized from resorcinol/formaldehyde gel, using WO 3 nanoparticles as starting material. Supporting materials have been characterized by BET (Brunauer, Emmett and Teller) technique and determined values of surface area were 80 m 2 g −1 for WCctabr and 175 m 2 g −1 for WC WO 3 . Platinum nanocatalysts (10% Pt) at tungsten based supports have been prepared by borohydride reduction method. Both synthesized supports and catalysts have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) techniques. Cyclic voltammetry was applied for determination of electrochemically active surface area (40 m 2 g −1 for Pt/WC WO 3 and 55 m 2 g −1 for Pt/WCctabr). Oxygen reduction reaction has been studied by cyclic voltammetry and linear sweep voltammetry at rotating disc electrode (RDE). These catalysts exhibited better catalytic activity, expressed in terms of kinetic current density per real surface area at the constant potential and better stability, in comparison with Pt/C catalyst, as well as with already reported catalytic activity values for Pt catalysts on tungsten based supports.

The influence of poisoning of MoOx-Pt catalyst by CO on the kinetics of H2 oxidation reaction (HOR) at MoOx-Pt electrode in 0.5 mol dm-3 HClO4 saturated with H 2 containing 100 ppm CO, was examined on rotating disc electrode (RDE) at 25 °C. MoOx-Pt nano-catalyst prepared by the polyole method combined with MoOx post-deposition was supported on commercial carbon black, Vulcan XC-72. The MoOx-Pt/C catalyst was characterized by TEM technique. The catalyst composition is very similar to the nominal one and post-deposited MoOx species block only a small fraction of the active Pt particle surface area. MoOx deposition on the carbon support can be ruled out from the EDAX results and from the low mobility of these oxides under used conditions. Based on Tafel-Heyrovsky-Volmer mechanism the corresponding kinetic equations from a dual-pathway model were derived to describe oxidation current-potential behavior on RDE over entire potential range, at various CO coverages. The polarization RDE curves were fitted with derived polarization equations according to the proposed model. The fitting showed that the HOR proceeded most likely via the Tafel-Volmer (TV) pathway. A very high electrocatalytic activity observed at MoOx-Pt catalyst for the hydrogen oxidation reaction in the presence of 100 ppm CO is achieved through chemical surface reaction of adsorbed CO with Mo surface oxides. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

The oxygen reduction reaction (ORR) was studied at carbon supported MoOx-Pt/C and TiOx-Pt nanocatalysts in 0.5 mol dm(-3) HClO4 solution, at 25 degrees C. The MoOx-Pt/C and TiOx-Pt/C catalysts were prepared by the polyole method combined by MoOx or TiOx post-deposition. Home made catalysts were characterized by TEM and EDX techniques. It was found that catalyst nanoparticles were homogenously distributed over the carbon support with a mean particle size about 2.5 nm. Quite similar distribution and particle size was previously obtained for Pt/C catalyst. Results confirmed that MoOx and TiOx post-deposition did not lead to a significant growth of the Pt nanoparticles. The ORR kinetics was investigated by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. These results showed the existence of two E - logj regions, usually observed with polycrystalline Pt in acid solution. It was proposed that the main path in the ORR mechanism on MoOx-Pt/C and TiOx-Pt/C catalysts was the direct four-electron process with the transfer of the first electron as the rate-determining step. The increase in catalytic activity for ORR on MoOx-Pt/C and TiOx-Pt/C catalysts, in comparison with Pt/C catalyst, was explained by synergetic effects due to the formation of the interface between the platinum and oxide materials and by spillover due to the surface diffusion of oxygen reaction intermediates. (C) 2008 Elsevier Ltd. All rights reserved. Euro-Interfinish 2007 Conference, Oct 18-19, 2007, Athens, Greece

The influence of poisoning of Pt catalyst by CO on the kinetics and mechanism of H2 oxidation reaction (HOR) at Pt/C electrode in 0.5 mol dm-3 HClO4, saturated with H2 containing 100 ppm CO, was examined with rotating disc electrode (RDE) at 22 °C. Commercial carbon black, Vulcan XC-72 was used as support, while Pt/C catalyst was prepared by modified polyol synthesis method in an ethylene glycol (EG) solution. The kinetically controlled current (Ik) for the HOR at Pt/C decreases significantly at CO coverage (ΘCO) > 0.6. For ΘCO < 0.6 the HOR takes place through Tafel-Volmer mechanism with Tafel reaction as rate-determining step at the low CO coverage, while Volmer step controls the overall reaction rate at the medium CO coverage. When CO coverage is higher then 0.6, Heyrovsky-Volmer mechanism is operative for the HOR with Heyrovsky as the rate-determining step (rds). © 2008 Elsevier Ltd. All rights reserved.

Ruthenium oxide/titanium oxide, with a Ru:Ti atomic ratio of 7:3 was synthesized by modified sol-gel procedure and used as a support for platinum nanocatalyst for oxygen reduction reaction. The synthesized materials were characterized in terms of morphology, particle size distribution, chemical and phase composition by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high angle annular dark filed scanning transmission electron microscopy (HAADF, STEM) and electron energy loss spectroscopy (EELS). XPS spectra revealed that Ru atoms were in mainly in Ru(4+) oxidation state, the Ti atoms in Ti(4+) oxidation state, whereas the Pt-atoms were in metallic state. TEM analysis proved that platinum nanoparticles nucleated at both oxide species and homogeneous distribution was observed. The average platinum nanoparticle size was 3.05 nm. Electrochemically active surface area of platinum was 32 m(2) g(-1). Kinetics of the oxygen reduction was studied at rotating disc electrode in 0.5 mol dm(-3) HClO4 solution, at 25 degrees C. The catalytic activities expressed in terms of specific activity (per electrochemically active surface area of platinum) and mass activity (per mass of platinum) were determined and compared to Pt catalyst on carbon support. The high catalytic activity was proven by electrochemical characterization. (C) 2014 Elsevier B.V. All rights reserved.

The underpotential deposition of hydrogen was studied in 0.5 mol dm-3 HClO4 solution on an electrode based on Ebonex-supported platinum electrocatalyst spread on rotation Au disk electrode (Ebonex/Pt). Pt catalyst was prepared by the impregnation method from 2-propanol solution of Pt(NH3)2(NO2)2 and Ebonex powder. Ebonex support (nonstoichiometric mixture of titanium oxides) was characterized by: X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and BET techniques. The synthesized catalyst was analyzed by TEM technique. Voltammetric profiles at the Ebonex/Pt catalyst surface in 0.5 mol dm-3 HClO4 aqueous solution obtained at different temperatures with the evaluation of the temperature effect on the reversible adsorption of the Hupd state are presented and the thermodynamic state functions for H adatom adsorption process are calculated. The chemisorptive energy strength of the Ebonex/Pt-H state is estimated in order to establish the relationship between the surface structure and the electrocatalytic activity of Ebonex/Pt electrode and compare it to the one for smooth polycrystalline Pt.

The mechanism and kinetics of the hydrogen evolution reaction were studied in 1.0 mol dm −3 NaOH solution on Fe–Mo alloy electrodes prepared by electrodeposition at constant current densities from a pyrophosphate bath. A series of electrode containing 34–59 at.% Mo was prepared. Electrodes displayed porous character, and electrochemical impedance spectroscopy was used to characterized real surface area. It was found that within the whole potential region the mechanism of the HER is a consecutive combination of the Volmer step, followed dominantly by a rate controlling Heyrovsky step, while the contribution of the parallel Tafel step is negligible. The kinetic parameters of the HER were determined. With an increase in the molybdenum content, the electrodes become more active, and an increase in the real surface area is observed. The main factor influencing the electrode activity seems to be the real surface area.

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. Fe–Mo legure su elektrohemijski taložene iz pirofosfatnog kupatila korišćenjem periodično promeljivog AC strujnog režima. Sastav i morfologija dobijenih taloga ispitivani su SEM i EDS tehnikama, dok je poprečni presek uzoraka ispitivan optičkom mikroskopijom, sa ciljem da se odredi uticaj uslova taloženja na morfologiju i sastav legura. Pokazano je da uslovi taloženja sastav kupatila i gustina struje taloženja, praktič no ne utiču na morfologiju legura, ali da utiču na sastav legura i na iskorišćenje struje njihovog taloženja. Takođe je pokazano da istaložene Fe–Mo legure posedujumanju prenapetost za reakciju izdvajanja vodonika od mekog čelika (0,15 V do 0,30 V u zavisnosti od uslova taloženja) koji se koristi kao katoda u industrijskim postrojenjima za proizvodnju hlorata, ukazujući da se elektrohemijski istaložene Fe–Mo legure mogu koristiti kao katalitički aktivne katode u ovom procesu.

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.

Platinum nanocatalyst at nano-tungsten carbide was synthesized, characterized and tested for oxygen reduction reaction (ORR) in 0.1 mol dm(-3) NaOH, at 25 degrees C. Tungsten-carbide islands on nano-tungsten particles (WC) was synthesized from gel prepared by using nanoparticles of WO3, previously produced from W-powder oxidized in H2O2. The support was porous material with high specific surface area (177 m(2)g(-1)). The WC supported Pt (10 wt.%) catalyst was prepared by borohydride reduction method. X-ray diffraction of the catalyst demonstrates successful reduction of Pt precursor to metallic form. STEM analysis of Pt/WC catalyst showed the existence of Pt particles lower than 2 nm in size, even the clusters of Pt atoms. Electrochemically active surface area of Pt was determined from adsorption/desorption charge of hydrogen atoms. Catalytic activity of the synthesized catalyst for ORR was studied by cyclic voltammetry and linear sweep voltammetry at rotating disk electrode. The onset potential on Pt/WC for ORR, comparing with Pt/Vulcan, was shifted to the positive potentials for about 150 mV. Pt/WC catalyst shows one Tafel slope of -0.105 V dec(-1), remarkable catalytic activity expressed either through the value of the current density per real surface area, or through the mass activity and excellent stability. (C) 2012 Elsevier Ltd. All rights reserved.

The catalytic activity of WC/Pt electrocatalysts towards hydrogen oxidation reaction (HOR) in acid solution was studied. Tungsten carbide (WC) prepared by polycondensation of resorcinol and formaldehyde in the presence of ammonium metatungstate salt and CTABr surfactant was used as the support of a Pt electrocatalyst (WC/Pt). The obtained WC/Pt electrodes were characterized by XRD, HRTEM, EDS, EELS and electrochemical measurements. HRTEM analysis showed that the WC particles possess a core–shell structure with a metallic tungsten core and a shell composed of a mixture of tungsten carbides shell (WC and W 2 C). The WC/Pt catalyst is composed of well-dispersed sub-nanometer Pt clusters which consist of a few to several tens of Pt atoms. EELS measurements indicate that the WC particles function as nucleation sites for Pt nanoparticles. Based on the Tafel–Heyrovsky–Volmer mechanism the corresponding kinetic equations were derived to describe the HOR current–potential behavior over the entire potential region on RDE. The fitting showed that in the lower potential region HOR on Pt proceeds most likely via the Tafel–Volmer (TV) pathway. The kinetic results also showed that the WC/Pt(1%) when compared to the standard C/Pt(1%) electrode led to a remarkable enhancement of the hydrogen oxidation in an acidic medium, which was explained by H-spill-over between platinum and tungsten carbide.

Platinum based nanocatalyst at home made Nb-TiO2 support was synthesized and characterized as the catalyst for oxygen reduction reaction in 0.1 mol dm(-3) NaOH, at 25 degrees C. Nb doped TiO2 catalyst support, containing 5% of Nb, has been synthesized by modified acid-catalyzed sol-gel procedure in non-aqueous medium. BET and X-ray diffraction (XRD) techniques were applied for characterization of synthesized supporting material. XRD analysis revealed only presence of anatase TiO2 phase in synthesized support powder. Existence of any peaks belonging to Nb compounds has not been observed, indicating Nb incorporated into the lattice. Nb-TiO2 supported Pt nanocatalyst synthesized, using borohydride reduction method, was characterized by TEM and HRTEM techniques. Platinum nanoparticles distribution, over Nb doped TiO2 support, was quite homogenous. Mean particle size of about 4 nm was found with no pronounced particle agglomeration. Electrochemical techniques: cyclic voltammetry and linear sweep voltammetry at rotating disc electrode were applied in order to study kinetics and estimate catalytic activity of this new catalyst for the oxygen reduction reaction in alkaline solution. Two different Tafel slopes were found: one close to -90 mV dec(-1) in low current density region and other approximately 200 my dec(-1) in high current density region, which is in good accordance with literature results for oxygen reduction at Pt single crystals, as well as Pt nanocatalysts in alkaline solutions. Similar specific catalytic activity (expressed in term of kinetic current density per real surface area) of Nb(5%)-TiO2/Pt catalyst for oxygen reduction reaction in comparison with the carbon supported platinum (Vulcan/Pt) nanocatalyst, was found. (C) 2011 Published by Elsevier Ltd.

The kinetics of the hydrogen oxidation reaction (HOR) was studied at Pt nanoparticles supported on niobia-doped titania (Pt/N-T). The catalyst support, with the composition of 0.05NbO2.5-?-0.995TiO2 (0

In order to point out the effect of the support to the catalyst for oxygen reduction reaction nano-crystalline Nb-doped TiO2 was synthesized through a modified sol-gel route procedure. The specific surface area of the support, S-BET, and pore size distribution, were calculated from the adsorption isotherms using the gravimetric McBain method. The support was characterized by X-ray diffraction (XRD) technique. The borohydride reduction method was used to prepare Nb-TiO2 supported Pt (20 wt.%) catalyst. The synthesized catalyst was analyzed by TEM technique. Finally, the catalytic activity of this new catalyst for oxygen reduction reaction was investigated in acid solution, in the absence and the presence of methanol, and its activity was compared towards the results on C/Pt catalysts. Kinetic analysis reveals that the oxygen reduction reaction on Nb-TiO2/Pt catalyst follows four-electron process leading to water, as in the case of C/Pt electrode, but the Tafel plots normalized to the electrochemically active surface area show very remarkable enhancement in activity of Nb-TiO2/Pt expressed through the value of the current density at the constant potential. Moreover, Nb-TiO2/Pt catalyst exhibits higher methanol tolerance during the oxygen reduction reaction than the C/Pt catalyst. The enhancement in the activity of Nb-TiO2/Pt is consequence of both: the interactions of Pt nanoparticles with the support and the energy shift of the surface d-states with respect to the Fermi level what changes the surface reactivity. (C) 2010 Elsevier B.V. All rights reserved.

The hydrogen oxidation reaction (HOR) was studied at the home made TiO(x)-Pt/C nanocatalysts in 0.5 mol dm(-3) HClO(4) at 25 degrees C. Pt/C catalyst was first synthesized by modified ethylene glycol method (EG) on commercially used carbon support (Vulcan XC-72). Then TiO(x)-Pt/C catalyst was prepared by the polyole method followed by TiO(x) post-deposition. The synthesized catalyst was characterized by XRD, TEM and EDX techniques. It was found that Pt/C catalyst nanoparticles were homogenously distributed over carbon support with the mean particle size of about 2.4 nm. The quite similar, homogenous distribution and particle size were obtained for Pt/C doped by TiO(x) catalyst which was the confirmation that TiO(x) post-deposition did not lead to significant growth of the Pt nanoparticles. The electrochemically active surface area of the catalyst was determined by using the cyclic voltammetry technique.The kinetics of hydrogen oxidation was investigated by the linear sweep voltammetry technique at the rotating disc electrode (RDE). The kinetic equations used for the analysis were derived considering the reversible or irreversible nature of the kinetics of the HOR. It was found that the hydrogen oxidation reaction for an investigated catalyst proceeded as an electrochemically reversible reaction. The values determined for the kinetic parameters-Tafel slope of 28 mV dec(-1) and exchange current density about 0.4 mA cm(-2)(Pt) are in good agreement with usually reported values for a hydrogen oxidation reaction with platinum catalysts in acid solutions.

The kinetics and mechanism of the hydrogen oxidation reaction were studied in 0.5 mol dm(-3) HClO(4) solution on an electrode based on titanium oxide with Magneli phase structure-supported platinum electrocatalyst applied on rotation Au disk electrode. Pt catalyst was prepared by impregnation method from 2-propanol solution of Pt(NH(3))(2)(NO(2))(2) and sub-stoichiometric titanium oxide powder. Sub-stiochiometric titanium oxide Support was characterized by X-ray diffraction and BET techniques. The synthesized catalyst was analyzed by TEM technique. Based on Tafel-Heyrovsky-Volmer mechanism the corresponding kinetic equations were derived to describe the hydrogen oxidation current-potential behavior on RDE over the entire potential region. The polarization RIDE curves were fitted with derived polarization equations according to proposed model. The fitting shows that the HOR on Pt proceeds most likely via the Tafel-Volmer (TV) pathway in the lower potential region, while the Heyrovsky-Volmer (HV) pathway is operative in the higher potential region. It is pointed out that Tafel equation that has been frequently used for the kinetics analysis in the HOR, can not reproduce the polarization curves measured with high mass-transport rates. Polarization measurements on RDE revealed that the Pt catalyst deposited on titanium suboxide support showed equal specific activity for the HOR compared to conventional carbon-supported Pt fuel cell catalyst. (C) 2008 Elsevier B.V. All rights reserved.

The oxidation of methanol and reduction of oxygen were studied on MoOx-Pt/C nano-catalysts prepared by the polyole method combined by MoOx post-deposition. The catalysts were characterized by TEM and EDX. The presented composition of the electrode is very similar to the nominal ones and post-deposited MoOx species block only a small fraction of the active Pt particle surface area. MoOx deposition on the carbon support can be ruled out from the EDX results and the low mobility of these oxides at corresponding conditions. The electrode catalytic activity in the electrooxidation of methanol and the reduction of oxygen was studied by steady-state voltammetry and cyclic voltammetry. MoOx-Pt/C catalyst exhibits higher catalytic activity than Pt/C for the oxygen reduction. The catalytic effect in oxidation of methanol is achieved only under potentiodynamic conditions, when poisoning species have no enough time to develop fully. (C) 2007 Elsevier B.V. All rights reserved.

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 (lcd), the Tafel slope was found to be close to -2.3RT/F, while at high current densities (hcd) it was found to be close to -2?2.3RT/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. .

Home-made carbon cryogel synthesized by sol–gel polycondensation and freeze-drying is used as support for preparation of highly dispersed Pt catalyst that is made by a modified polyol synthesis method in an ethylene glycol (EG) solution. Specific surface area of carbon support and Pt/C catalyst is determined from nitrogen adsorption isotherm. The adsorption isotherm demonstrates a significant mesoporosity of carbon support. Specific surface area of the carbon support, calculated by the BET equation, is found to be 573 m 2 g - 1 . X-ray diffraction (XRD) results demonstrate a successful reduction of the Pt precursor to its metallic form, and transmission electron microscopy (TEM) images show very uniform Pt particle size distribution with mean particle size of about 2.7 ± 0.7 nm of the catalyst. Potentiodynamic studies of the underpotential deposition of hydrogen ( H upd ) on Pt/C electrode in 0.5 mol dm - 3 HClO 4 aqueous solution in the temperature range from 274 to 318 K are made, and thermodynamic state functions for the hydrogen adsorption are determined. The experimental results are analyzed assuming linear variation of the Gibbs energy of adsorption versus θ H upd on the basis of the surface heterogeneity. The increase of Δ G H upd θ with the surface coverage indicates the repulsive interactions between H upd adatoms. From the temperature dependence of the Gibbs energy of adsorption, the enthalpy and the entropy of adsorption are calculated. The values of these functions are determined to be Δ H H upd θ = 0 = - 5.6 kJ mol - 1 and Δ S H upd θ = 0 = 69.1 J mol - 1 K - 1 . The value of Δ H H upd θ allows determinations of the bond energy between electrode surface and H upd that is found to be E Pt – H = 223 kJ mol - 1 for θ = 0 .