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

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 ail electrolyte commonly used in commercial chlorate production, depending on the alloy composition, i.e., the conditions of alloy electrodeposition

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

Uticaj prisustva volfram-karbida u ugljeničnom nosaču Pt nanočestica na elektrohemijsku redukciju kiseonika u kiselom rastvoru

Tungsten carbide was synthesized by calcination of carbon cryogel with embedded tungsten in a form of metatungstate. This material was used as a support for Pt nanoparticles. XRD pattern of W-C support indicated the presence of WC, W2C, and unreacted W, as well as graphitized carbon. According to previous TEM analysis of W-C support, it contains particles with core-shell structure, where the W particle was covered with the shell of a mixture of WC and W2C. The average Pt grain size calculated from XRD pattern was about 6 nm. A cyclic voltammogram of W-C support was recorded within the potential range relevant for its application as a catalyst support in fuel cells. The pair of anodic/cathodic peaks close to the negative potential limit could be ascribed to the intercalation of hydrogen within hydrous tungsten oxide, which is always present on the surface of WC in aqueous solutions. The cyclic voltammogram of Pt/W-C indicated that tungsten oxide species are present on tungsten carbide shell as well as on the surface of Pt nanoparticles. The Pt surface is only partially covered by hydrous tungsten oxide. Hydrogen intercalation in hydrous tungsten oxide is enhanced in the presence of Pt nanoparticles. Also, the presence of hydrated tungsten oxide leads to the decrease of OH chemisorbed on Pt surface. Stripping of underpotentially deposited copper was used for the assessment of Pt surface area and the specific surface area of Pt was estimated to be 41 m2 g-1. The electrochemical oxygen reduction reaction was examined on the synthesized Pt/W-C catalyst and compared with the results on the commercial Pt/C catalyst. It was found that the current densities at Pt/W-C were almost twice as high as those on Pt/C. The Tafel plots for both catalysts are characterized with two Tafel slopes: -0.060 V dec-1 at low current densities, and -0.120 V dec-1 at high current densities. From the rotational dependence of the reaction rate, it was found that oxygen reduction on both Pt/W-C and Pt/C follows the first order kinetics with respect to O2 and that four electrons are transferred per O2 molecule. The results show that the presence of tungsten carbide in support material, i.e. hydrous tungsten oxide on Pt surface, leads to promotion of oxygen reduction on the Pt/W-C catalyst. It was assumed that oxophilic hydrated tungsten oxide hinders OH adsorption on Pt surface, thus increasing Pt surface area available for O2 adsorption and its electrochemical reduction.Sintetizovan je nosač katalizatora u kojem se na ugljeničnoj osnovi nalaze nanočestice metalnog volframa obavijene volfram-karbidom i na njega su nanete nanočestice Pt. Karakterizacija sintetizovanog uzorka cikličnom voltametrijom u kiseloj sredini ukazala je na oksidaciju volframovih vrsta iz nosača i formiranje hidratisanih oksidnih vrsta volframa na površini Pt. Elektrohemijska redukcija O2 u kiseloj sredini je ispitivana na sintetizovanom uzorku i rezultati su upoređeni sa komercijalnim katalizatorom u kojem su nanočestice Pt na nosaču od ugljenika razvijene površine. Pokazano je da redukcija O2, bez obzira na nosač katalizatora, sledi kinetiku prvog reda po O2 uz razmenu četiri elektrona, ali da su gustine struje veće u slučaju nosača sa volfram-karbidom. Povećana aktivnost sintetizovanog katalizatora je posledica prisustva oksofiličnih hidratisanih oksida volframa koji sprečavaju adsorpciju hidratisanog oksida na površini Pt i tako povećavaju površinu Pt dostupnu za adsorpciju i redukciju molekula kiseonika

Ru layers electrodeposited onto highly stable Ti2AlC substrates as cathodes for hydrogen evolution in sulfuric acid solutions

In this work, the hydrogen evolution reaction (HER) was studied on Ru coated Ti2AlC electrodes in 1.0 mol dm(-3) H2SO4 at 25 degrees C. Ti2AlC was found to be a highly stable substrate in sulfuric acid solutions due to the formation of a passivating oxide layer on the surface, which was confirmed by the X-ray photoelectron spectroscopy (XPS) analysis of as-prepared and anodically treated Ti2AlC samples. Ru films were electrodeposited onto Ti2AlC substrates by cycling the potential of Ti2AlC in the solution containing 0.01 mol dm(-3) RuCl3 + 0.1 mol dm(-3) H2SO4 between -0.5 V and 0.4 V vs. a saturated calomel electrode (SCE) at the sweep rate of 20 mV s(-1). Four Ru/Ti2AlC samples were prepared, obtained at 5, 10, 15 and 20 cycles of Ru electrodeposition. Characterization of samples was performed by scanning electron microscopy (SEM) and cyclic voltammetry (CV), while the thickness of the electrodeposited Ru layers was determined by atomic force microscopy (AFM). It was found that the most compact sample with the thickness of about 0.42 mu m was obtained after 5 cycles. Electrochemical impedance spectroscopy (EIS) and steady-state polarization measurements showed that all Ru/Ti2AlC electrodes were exceptionally active for the HER. A Tafel slope of about -60 mV dec(-1) was observed on all polarization curves in the range of high cathodic current densities. Based on formal kinetics analysis, an appropriate mechanism for the HER on Ru/Ti2AlC was suggested.This is the peer-reviewed version of the article: Jovic, B. M., Jović, V. D., Lačnjevac, U., Stevanović, S., Kovac, J., Radovic, M.,& Krstajić, N. V. (2016). Ru layers electrodeposited onto highly stable Ti2AlC substrates as cathodes for hydrogen evolution in sulfuric acid solutions. Journal of Electroanalytical Chemistry, Elsevier, 766, 78-86. [https://doi.org/10.1016/j.jelechem.2016.01.038]The published version: [https://cer.ihtm.bg.ac.rs/handle/123456789/2012

Spectrophotometric study of the anodic corrosion of Ti/RuO2 electrode in acid sulfate solution

Electrochemical properties of RuO2-based electrode, particularly the oxygen evolution and anodic dissolution of RuO2 have been investigated in 0.5 mol dm-3 H2SO4 solution by means of polarization measurements and product analysis. It has been demonstrated that it is possible to determine very low concentration of dissolved ruthenium species (8 × 10-10 mol dm-3 Ru) by a sensitive spectrophotometric method based on the ruthenium-catalyzed ceric-arsenite reaction.Finally, the probable mechanism of anodic dissolution of RuO2-based electrode, has been proposed

Ispitivanje anodnog ponašanja mekog čelika u različitim rastvorima u cilju izbora elektrolita za elektrohemijsku sintezu filmova elektroprovodnih polimera

In this paper the anodic behavior of mild steel in the different solutions of the organic and the inorganic electrolytes, with the aim to select the electrolyte for the electrochemical synthesis of electro conducting polymer films. On the basis of anodic polarization and galvanastatics curves, a solution of the sodium-benzoate and sodium-nitrite has been found to be potentially good electrolytes for the syntheses of electro conducting polymer films.U radu je ispitano anodno ponašanje mekog čelika u različitim rastvorima organskih i neorganskih elektrolita, u cilju izbora elektrolita za elektrohemijsku sintezu filmova elektroprovodnih polimera. Na osnovu anodnih potenciostatskih i galvanostatskih krivih ustanovljeno je da rastvori natrijum-benzoata i natrijum-nitrita mogu biti potencijalno dobri elektroliti za sintezu filmova elektroprovodnih polimera

The influence of polypyrrole films on the corrosion behavior of iron in acid sulfate solutions

The corrosion behavior of mild steel covered by electrodeposited polypyrrole films was investigated by electrochemical impedance spectroscopy. Electrodeposition of polypyrrole was performed from an aqueous solution of pyrrole and oxalic acid at a constant current density of 1 mA/cm(2) and yields strongly adherent and smooth polymer layers. The non-linear least squares (NLS) fitting was applied to the impedance spectra to estimate the parameters of the proposed equivalent circuit, based on a physical model for the corrosion of mild steel protected by polypyrrole films in acid sulfate solutions

Fundamental aspects of plating technology II: Morphological aspects of metal electrodeposition from complex salt solutions

It is shown that the improved quality of electrodeposits obtained from ammonium complex salt solutions compared with deposits obtained from simple salt solutions is due to the decrease in the exchange current density value for the deposition process

Kinetics of the hydrogen evolution reaction on Fe-Mo film deposited on mild steel support in alkaline solution

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