Galvanic Deposition Research Articles

Investigation of the Gas Permeation Stream through Gas Diffusion Electrodes for CO2 Electrolysis and Possible Links to Selectivity

The electrochemical reduction of CO2 (eCO2R) is one promising attempt to create value added products from excess greenhouse gas with renewable energy. However, to become commercially relevant, some challenges have to be outgrown. To overcome the challenge of mass transport limitations on planar electrodes, Gas-Diffusion-Electrodes (GDE) have been implemented for eCO2R, allowing to reach sufficient reaction rates with the CO2 directly being delivered to the catalyst layer [1]. A major issue in the application of GDEs for eCO2R represents flooding of the mostly carbon based gas diffusion media by the alkaline electrolyte during application. This phenomenon results in a detrimental change of the 3-phase boundary and is accompanied by a loss of activity and a breakdown of performance [2]. A possible approach to avoid flooding of the GDE during eCO2R is to apply a backpressure in order to increase the capillary pressure inside the GDE, which needs to be balanced accurately, since excess backpressure can cause a CO2 crossover stream through the GDE into the electrolyte compartment [3]. In our work we investigate the permeation behavior of GDEs in a customized flow cell and investigate how to influence it via electrode preparation. A deeper understanding of the permeation characteristics of GDEs could lead to a better choice of operation points regarding flooding issues. However, the operation point itself and the preparation of GDEs could impact not only the flooding behavior of the electrode but also selectivity of the reaction. The eCO2R is taking place ~10 µm away from the gas-liquid boundary. The distribution of the two phases inside the GDE is crucial for the reaction pathway [4]. Therefore, we examine possible links of permeation behavior and electrode preparation on selectivity.In detail, our setup contains a customized flow cell in which the pressure in the gas compartment is adjusted with a needle valve and monitored via a pressure transmitter. The gas-crossover stream through the GDE is then registered by collecting the gas transferred to the liquid electrolyte in a measuring cylinder.For electrode preparation, commercial carbon based GDLs (25BC-Sigracet, H23C8-Freudenberg) are pretreated by either spray coating a carbon-ionomer-layer on top of the microporous layer or sputter coating with copper first. In the second step, a galvanostatic deposition of copper is carried out on the pretreated GDLs.The permeation behavior is tested for the non-coated commercial GDLs, the GDLs after the pretreatment step and after deposition of copper without and with current applied, respectively. In our experiments the crossover stream related to backpressure through the GDL H23C8 was lower compared to the crossover stream through GDL 25BC, most likely being linked to differences in the porosity and cracks of the MPL (Figure 1A). However, when comparing identically prepared GDEs based on different GDL types at the same crossover stream, only minor changes in selectivity can be observed (Figure 1B). It was also found that the crossover stream was influenced by the coating of the electrode. While sputter coating (spu) has a minor impact on gas permeation, spray coating (spr) leads to a significant change. These observations could be related to increased electrode wetting after spray- but not after sputter coating. The permeation behavior after galvanic deposition of copper is comparable, independent of the pretreatment procedure. Comparing the selectivity of GDEs with the different pretreatment procedure, a significant change in selectivity can be observed (Figure 1C). In the next steps, it will be crucial to investigate if this selectivity change is related to a different gas-liquid distribution in the GDE or to other factors as the composition of the coating layer to successfully influence operation stability and selectivity.

(Invited) In Situ x-Ray Diffraction Studies of the Atomic Structure and Charge Distribution at the Electrochemical Interface

The presence of specifically adsorbed anions can significantly affect the electrochemical reactivity of a metal electrode which is of major interest for galvanic deposition, etching, corrosion and electrocatalysis. In-situ surface x-ray diffraction has enabled an atomic/molecular-level understanding of the interface under reactive conditions, including its potential and time dependence, to be developed. While information about the atomic structure of the electrode surface in electrochemical in-situ cells has been widely investigated, insight into the charge distribution and the structure of the electrolyte at the interface is still lacking. Advances in these directions offer possibilities in elucidating atomic scale models of the electrochemical interface and thus will help to establish structure-stability-reactivity relationships.A fundamental understanding of the nature of the charge transfer, especially the influence of the applied potential and the screening by the electrolyte, is a major goal in electrochemistry to better understand electrochemical processes and charge transfer during adsorption and deposition. [1]Thus, combining x-ray spectroscopy and x-ray diffraction to gain site specific information about the charge distribution at buried interfaces is a promising tool. [2,3]Examples of how the use of surface x-ray scattering techniques can help to characterize electrochemical interfaces in-situ in order to link, structure, reactivity and stability will be presented. [4-5] Advances in these directions offer possibilities in elucidating atomic scale models of the electrochemical interface and thus will help to establish structure-stability-reactivity relationships and to understand growth kinetics and electrochemical phase formation.

Evaluation of Nickel-Iron (Oxy)Hydroxide Catalysts in Varied Electrode Geometries Under Industrially Realistic Conditions for Enhanced Alkaline Water Electrolysis

In pursuit of realizing a hydrogen-based economy, the challenge lies in enhancing the efficiency of crucial water electrolysis technologies. Alkaline water electrolysis (AWE) holds promise as an ecologically friendly method for H2 production, primarily due to its capacity for employing non-precious metals as electrocatalysts, in contrast to more costly options which can only switch to noble metals such as ruthenium or iridium. However, this technology faces a significant challenge arising from the sluggish kinetics of the oxygen evolution reaction (OER), which constrains the overall efficiency. [1] Furthermore, the limited stability of many OER catalysts alternatives developed at lab scale and less harsh conditions poses a substantial obstacle to the commercialization of this technology.[2] To overcome this issue, the development of highly active OER catalysts that maintain their activity under industrial conditions is of major importance explaining the growing attention that this topic is gaining in literature. Nevertheless, most of the reported systems are tested at low current densities under easily manageable conditions in the laboratory (≤ 100 mA cm-2, 1 M KOH, RT). Without disagreeing that this approach is necessary to identify promising options among the numerous catalyst systems, it is not sufficient when competing with existing technologies that already achieve high current densities. In this context, we investigate a low-cost, abundantly available non-precious metal based OER-catalyst under industrially relevant conditions (≤ 1.2 A cm-2, 30 wt.-% KOH, 80 °C). The synthesis is based on a multistep galvanic deposition method introduced by Wu et al [3], receiving a highly porous NiFeOOH catalyst. Addressing the complexity of the multiphase process of AWE that involves gas-liquid-solid interfaces, the catalyst system is transferred to numerous nickel electrodes with different 3D geometries (plain woven mesh, knitted mesh, expanded metal mesh) for the investigation of their impact on bubble formation and detachment. To further optimize the catalyst system a variation of the iron content with respect to its’ molar fraction relatively to nickel has been carried out from x(Fe)=0 to x(Fe)=0.75, which after synthesis were first examined using SEM and EDS. The structure can be considered as pompom-shaped particles, forming a porous framework, as can be seen exemplarily in Figure 1a) on a knitted nickel-wire mesh coated with NiFeOOH. Observing variations in iron content, it becomes evident that a higher iron content results in larger particle sizes, thereby altering pore sizes. However, the surface morphologies of each catalyst until a molar fraction x(Fe)=0.5 is reached, can be considered as very similar. When comparing the SEM images of the mesh with a molar fraction x(Fe)=0.75 to the other molar fractions, a secondary phase becomes apparent on the surface. Notably, the porous structure persists within the crystalline phase. It could be shown by EDS that the target values for the molar fractions set in the galvanic bath and the actual molar fractions nearly show no deviations. Further, a uniform dispersion of Ni, Fe and O is observed.The electrochemical investigation of the prepared catalysts was done in a 3-electrode PTFE beaker cell setup in 30 wt % KOH and at 80 °C. The measurement protocol we introduce consists of galvanostatic steps between 0-1.2 A cm-2. The stability is tested chronopotentiometrically as well by maintaining a current density of 500 mA cm-2 for 100 h. It becomes apparent that no optimum is reached in the tested range of iron content and that the potential continues to drop as the molar fraction of Fe increases, achieving the lowest potential with 1.38 V vs. RHE at 50 mA cm-2 and 1.42 V vs. RHE at 750 mA cm-2 with x(Fe)=0.75. It could be further proved that the NiFeOOH catalyst with x(Fe)=0.75 is a highly stable catalyst, resulting in a potential increase of 27 mV over 100 h of testing at 500 mA cm-2, making it to an appropriate OER catalyst for the application in the AWE. The highly porous structure is maintained after testing, proved by SEM imaging. The iron contents after testing are also very similar, which means that there is almost no iron loss in the coating. For the different tested electrode geometries coated with NiFeOOH (x(Fe)=0.5), similar activity is observed, shown in Figure 1b) with a ranging potential between 1.38 V to 1.41 V vs. RHE at 50 mA cm-2 and 1.42 V to 1.45 V vs. RHE at 750 mA cm-2.[1] a) Cao et al., Energy Environ. Sci. 2012 b) Zhao et al., ACS Chemical Reviews 2023.[2] Zeng et al., Journal of Energy Chemistry 2022.[3] Wu et al., Applied Surface Science 2021. Figure 1

Imparting a better corrosion resistance and bioactivity for magnesium through the formation of zinc - zinc oxide - zinc phosphate (hopeite) - magnesium ammonium phosphate (struvite) composite coatings

The present study aims to develop zinc-zinc oxide-zinc phosphate (hopeite)-magnesium ammonium phosphate (struvite) composite coatings to reduce the rate of degradation and to impart a better bioactivity for Mg. Galvanic deposition was employed to form Zn-ZnO coating on Mg, which was subsequently converted to hopeite and struvite by chemical conversion method using diammonium hydrogen phosphate. The structural and morphological characteristics, nature of functional groups, degradation behaviour in Hanks’ balanced salt solution (HBSS) and bioactivity in simulated body fluid (SBF) were evaluated. The findings of the study revealed that Zn-ZnO-hopeite-struvite composite coating has considerably reduced the rate of degradation of Mg in HBSS and promoted the bioactivity of Mg in SBF. The rate of degradation of Mg is decreased from 1.27 ± 0.11 mm/y to 0.13 ± 0.04 mm/y, amounting to ⁓90 % reduction in the corrosion rate. The morphological features reveal that the extent of corrosion attack on Zn-ZnO-hopeite-struvite composite coated Mg is very much limited when compared to that of the uncoated one. The surface of Zn-ZnO-hopeite-struvite composite coated Mg shows many thin needle-like crystals as well as globular-like particles after immersion in SBF when compared to that of uncoated and Zn-ZnO coated Mg. The uniform and compact coating with good adherence, improved corrosion resistance and better bioactivity suggest that Zn-ZnO-hopeite-struvite composite coating is a promising surface modification approach towards the development of Mg-based degradable implants.

ИССЛЕДОВАНИЕ КОРРОЗИОННОЙ СТОЙКОСТИ ГАЛЬВАНИЧЕСКИХ ПОКРЫТИЙ СПЛАВОМ КОБАЛЬТ-МОЛИБДЕН

Studies have been carried out on the corrosion resistance of cobalt-molybdenum galvanic deposits of various thicknesses obtained from tartrate electrolytes using direct and pulsed currents. The influence of coating thickness and molybdenum content on its anti-corrosion protective properties has been established. An optimal electrolyte composition for obtaining Co-Mo coating has been proposed. A hypothesis has been put forward about the reasons for the high corrosion resistance of the resulting alloy.

Electrocrystallization of Cu, Sn, and Сu-Sn alloys from sulfate electrolytes in the presence of thiourea and N-octylpyridinium bromide: Experimental and computational studies

Galvanic deposition of copper, tin and their alloys is widely used in microelectronics, printed circuit boards, anticorrosive and decorative finishing of products for various purposes. One of the main factors determining the structural and morphological characteristics of the deposited coatings is the value of cathodic polarization during the deposition, which depends on the presence of complexing ions and surfactants. Complexation is one of the most effective and widespread ways to increase the cathodic polarization, as well as the convergence of deposition potentials of copper and tin. In this work we studied the combined effect of thiourea and N-octylpyridinium bromide additives on the kinetics of Cu, Sn, and Cu-Sn electrocrystallization from sulfuric acid electrolytes. The combined presence of these additives allows obtaining homogeneous and fine-grained Cu-Sn coatings. The results of theoretical studies agree well with experimental data and show that the introduction of thiourea and N-octylpyridinium bromide leads to the inhibition of cathodic reduction of hydrated copper(II) and tin(II) ions.

Novel Electrode Designs and Configurations in Secondary Iron-Air Batteries

Stationary energy storage solutions are urgently needed due to the challenges we face caused by the anthropogenic climate change. While Lithium-Ion batteries are still considered as state of the art within this field, the availability of lithium is limited.The iron-air battery system is mainly superior due to the low criticality of the active materials. Iron is cheap and abundant, while air is supplied by the ambient atmosphere. During discharging oxygen from ambient air is reduced (oxygen reduction reaction, ORR) and evolved during charging (oxygen evolution reaction, OER). One of the main challenges towards stable metal-air batteries is the air-electrode. Those usually consist of a catalyst, a conductive additive, and – depending on the electrode design- of a binder. Carbon-based materials offer an excellent intrinsic activity towards the oxygen reduction and a high specific surface area. However, carbon corrodes in the potential range of the oxygen evolution reaction. Our work focuses on the development of novel electrode formulations for PTFE-bonded electrodes and novel self-supported electrode structures - based on galvanic deposition of nickel - and their implementation in iron-air batteries.Within a first approach a mixed catalyst composed of MnO2 and NiO was investigated in a PTFE-bonded electrode with nickel as conductive additive. The electrode reached an initial activity of 0.77 V vs. RHE @ -25 mA cm-2 (ORR) and 1.57 V vs. RHE @ 25 mA cm-2 (OER) in 6 M KOH at room temperature. The potentials were stable for about 60 cycles (one cycle consisted of 60 min). MnO2 corrodes at OER potentials, which results in a decrease of activity. However, a partial substitution of MnO2 by NiO is beneficial for the cycling stability. In a second approach, a bifunctional nickel-cobalt-oxide based bifunctional catalyst was investigated within the same electrode system. An initial activity of 0.71 V vs. RHE and 1.63 V vs. RHE was observed for this system. Stable OER performance but a decrease ORR activity was observed within this system over time during cycling. To increase the cycling stability, dendritic nickel structures with a high intrinsic surface area were prepared with galvanic deposition. Our results indicate that the efficiency and stability of the battery can be improved by using this approach. Figure 1

Silver─Gallium Nano‐Amalgamated Particles as a Novel, Biocompatible Solution for Antibacterial Coatings

AbstractBacterial infections account for countless deaths globally. Antibiotics are the primary countermeasure; however, the alarming spread of antibiotic‐resistant strains necessitates alternative solutions. Silver and silver compounds have emerged as promising antibacterial agents. However, issues related to cytotoxicity and genotoxicity of silver remain concern. To overcome these challenges, this proposes an easy‐to‐control and straightforward method to synthesize novel Silver─gallium (Ag─Ga) nano‐amalgamated particles. Gallium liquid metal (GaLM) is used to facilitate the galvanic deposition of silver nanocrystals (Ag) on oxide layer. The GaLM not only serves as a carrier for silver through the galvanic replacement process, but also provides a controlled‐release mechanism for silver, in this way improving biocompatibility, reducing inflammation, and stimulating bone growth. Notably, Ag─Ga suspensions can be conveniently deposited by spray‐coating on a range of devices and material surfaces, effectively eliminating pathogenic bacteria with efficacy comparable to that of silver ions. In vivo studies in rat models affirm the antibacterial capabilities, especially against methicillin‐resistant Staphylococcus aureus and Escherichia coli, when placed on implants such as titanium rods and magnesium discs. Furthermore, Ag─Ga promotes bone matrix formation and collagen growth without eliciting an inflammatory response, indicating a major promise for coatings on a wide variety of biomedical devices and materials.

Evaluation of Dimensional Characteristics of Conductive Pattern Elements of 3D-Printed Circuit Boards

Introduction. A review of foreign publications on 3D printing methods shows the possibility of their application for the manufacture of printed circuit boards (PCBs), while demonstrating the growth of interest in this field. One of the available methods is fused deposition modeling, which can be used to form substrates with channels for traces. At present, the minimum channel width comprises 100 µm, which corresponds to the 5th class of PCB accuracy. However, there is no data on how to obtain such dimensions or on the magnitude of their deviation from the given nominal values.Aim. To determine the influence of such factors as nozzle diameter and the number of contours on the dimensional characteristics of PCBs (linear dimensions; trace channel width; trace spacing; via diameters).Materials and methods. To obtain linear models, a full factorial experiment was carried out. The influence of the following materials was evaluated – polylactide (PLA), acrylonitrile butadiene styrene (ABS) and glass-filled ABS; slicers – Ultimaker Cura and PrusaSlicer; 3D printers – Picaso 3D Designer Classic 2016 and Hercules Strong 2017; brass nozzle with diameters ∅0.2 and ∅0.4 mm. The possibility of using brass nozzles coated with chemical nickel for printing with glass-filled filaments was considered. The study was conducted using the facilities of the "Center for Additive Technologies" of Bauman Moscow State Technical University.Results. The possibility of manufacturing PCBs up to the 2nd and 3rd accuracy classes using nozzles with a diameter of ∅0.4 and ∅0.2 mm, respectively, was shown. It was found that galvanic deposition of chemical nickel on a ∅0.2 mm brass nozzle makes it possible to increase the PCB wearability when printing with glass-filled filaments. Recommendations are proposed for selecting an optimal combination of nozzle diameter and the number of contours.Conclusion. The conducted analysis of mathematical models shows the significance of such parameters as nozzle diameter and the number of contours. The results can be used when creating new PCB layouts

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.

Properties and Structure Electrodeposition Alloys and Composite Electrochemical Coatings of Nickel-Based

The physicomechanical properties and morphology of composite electrochemical coatings (CEC) nickel-cobalt-nanodiamond from a chloride electrolyte-colloid of optimal composition have been investigated. For this CEC, microhardness (21-25 GPa) and internal compressive stresses (150-210 GPa) were determined. The study of wear and the Corrodcoot-test of the CEC showed a higher wear resistance (1,5 times) and the protective ability (2-3 times) of the CEC in comparison with chrome coatings. Studies of the CEC morphology and the nickel-cobalt alloy showed that the roughness of the resulting deposits, in comparison with nickel coatings, is 10 times less, and the fractal dimension of the coating surface is of the greatest importance. The cubic type of the nickel-cobalt-nanodiamond CEC lattice is established. The leveling effect on the structure of galvanic deposits of nanodiamond introduced from outside, as well as of microheterogeneous nickel and cobalt compounds formed in the electrolyte-colloid, has been determined.

Features of the Process of Galvanic Deposition of Metals into the Pores of Ion Track Membranes

Features of the Process of Galvanic Deposition of Metals into the Pores of Ion Track Membranes

Features of the Process of Galvanic Deposition of Metals into the Ion Track Membranes’ Pores

The paper considers some aspects of obtaining metal nanowires by matrix synthesis based on track membranes. In the first part of the paper, the main ideas of the method are considered and a review of the literature on the synthesis of nanowires of various types of single component (from one metal) and multicomponent—from two or more metals is given. In the second part of the review, variants of obtaining homogeneous structures of so-called alloyed nanowires and heterogeneous structures of so-called layered nanowires are considered. Several specific features of the electrodeposition method during the process in a limited volume of membrane pores are considered. In the second part of the work, the experimental results obtained by the authors in the study of electrodeposition of nanowires made of an iron–nickel alloy are considered. The so-called abnormal electrodeposition of iron was detected. The dependence of the integral element composition of the obtained nanowires on the pore diameter and on the growth voltage is discussed. Data on the nature of the distribution of elements along the length of nanowires are obtained. The unevenness of the composition is determined by the conditions of production (in particular, the different diffusion mobility of ions in narrow pore channels) and also depends on the voltage and diameter of the pore channels. Based on the X-ray diffraction data, the type of lattice (hcc) is determined and the nature of the change in the lattice parameter is shown, presumably associated with the difference in the ionic radii of metals.

CRISPR Cas12a-Powered Silicon Surface-Enhanced Raman Spectroscopy Ratiometric Chip for Sensitive and Reliable Quantification

Sensitive and reliable clustered regularly interspaced short palindromic repeats (CRISPR) quantification without preamplification of the sample remains a challenge. Herein, we report a CRISPR Cas12a-powered silicon surface-enhanced Raman spectroscopy (SERS) ratiometric chip for sensitive and reliable quantification. As a proof-of-concept application, we select the platelet-derived growth factor-BB (PDGF-BB) as the target. We first develop a microfluidic synthetic strategy to prepare homogeneous silicon SERS substrates, in which uniform silver nanoparticles (AgNPs) are in situ grown on a silicon wafer (AgNPs@Si) by microfluidic galvanic deposition reactions. Next, one 5'-SH-3'-ROX-labeled single-stranded DNA (ssDNA) is modified on AgNPs via Ag-S bonds. In our design, such ssDNA has two fragments: one fragment hybridizes to its complementary DNA (5'-Cy3-labeled ssDNA) to form double-stranded DNA (dsDNA) and the other fragment labeled with 6'-carboxy-X-rhodmine (ROX) extends out as a substrate for Cas12a. The cleavage of the ROX-tagged fragment by Cas12a is controlled by the presence or not of PDGF-BB. Meanwhile, Cy3 molecules serving as internal standard molecules still stay at the end of the rigid dsDNA, and their signals remain constant. Thereby, the ratio of ROX signal intensity to Cy3 intensity can be employed for the reliable quantification of PDGF-BB concentration. The developed chip features an ultrahigh sensitivity (e.g., the limit of detection is as low as 3.2 pM, approximately 50 times more sensitive than the fluorescence counterpart) and good reproducibility (e.g., the relative standard deviation is less than 5%) in the detection of PDGF-BB.

Effect of temperature on the current-voltage characteristics of PdFe/Cu and NiCo/Cu bimetallic catalysts in alkaline alcohol electrolytes

The temperature rise effect on the electrochemical activity of catalysts on a copper substrate in alkaline alcohol solutions has been studied. The object of research was bimetallic PdFe/Cu and NiCo/Cu catalysts obtained by galvanic deposition on a copper substrate. The studies were carried out in immiscible liquids EtOH + K2HPO4 + H2O. The upper phase in this system of liquids is aqueous solutions of ethanol (“alcohol layer”), the lower phase is aqueous solutions of dipotassium phosphate K2HPO4 (“salt layer”). It was found that elevate temperature from 20°C to 60°C improve the activity of all catalysts. It was found that the Ni80Co20/Cu catalyst is highly active in the oxidation and reduction of oxygen. The peak of the oxidation current increases 4 times with elevate the temperature up to 40 C, and 14 times with elevate temperature up to 60 C, compared with currents at a temperature of 20 C. The Pd90Fe10/Cu catalyst is active in relation to the oxidation of ethanol. Elevate the electrolyte temperature from 20°C to 40°C increase in the oxidation current by a factor of 1.4, and from 20°C to 60°C by a factor of 3.3. The maximum cathode current at the peak of recovery exceeds the maximum anode current at the peak of oxidation at 40°C by 1.83 times, and at 60°C by 1.15. This indicates a good regeneration of the electrode surface and the absence of oxide films and ethanol oxidation products on its surface. It was concluded that, despite the ambiguous effect of temperature on the processes occurring in the system, the improvement in the characteristics of the studied catalysts can be explained by the improvement in the processes of ethanol oxidation and improved mass transfer of the reagents.

3D reticulated vitreous carbon as advanced cathode material in galvanic deposition process

3D reticulated vitreous carbon as advanced cathode material in galvanic deposition process

Methanol Oxidation at Platinum Coated Black Titania Nanotubes and Titanium Felt Electrodes.

Optimized Pt-based methanol oxidation reaction (MOR) anodes are essential for commercial direct methanol fuel cells (DMFCs) and methanol electrolyzers for hydrogen production. High surface area Ti supports are known to increase Pt catalytic activity and utilization. Pt has been deposited on black titania nanotubes (bTNTs), Ti felts and, for comparison, Ti foils by a galvanic deposition process, whereby Pt(IV) from a chloroplatinate solution is spontaneously reduced to metallic Pt (at 65 °C) onto chemically reduced (by CaH2) TNTs (resulting in bTNTs), chemically etched (HCl + NaF) Ti felts and grinded Ti foils. All Pt/Ti-based electrodes prepared by this method showed enhanced intrinsic catalytic activity towards MOR when compared to Pt and other Pt/Ti-based catalysts. The very high/high mass specific activity of Pt/bTNTs (ca 700 mA mgPt−1 at the voltammetric peak of 5 mV s−1 in 0.5 M MeOH) and of Pt/Ti-felt (ca 60 mA mgPt−1, accordingly) make these electrodes good candidates for MOR anodes and/or reactive Gas Diffusion Layer Electrodes (GDLEs) in DMFCs and/or methanol electrolysis cells.

CORROSION RESISTANCE OF GALVANIC NICKEL DEPOSITS AND ELECTROCHEMICAL ACTIVITY OF THEIR CORROSION PRODUCTS

Background. Bright galvanic nickel coatings, with high sulphur content, are less corrosion resistant than matte. Bright nickel coatings are particularly susceptible to corrosion damage in conditions that simulate tropical humid climates and are characterized by the presence of acetic acid vapours. Objective. The purpose of the paper is to investigate: corrosion resistance of galvanic nickel deposits in concentrated acetic acid and its vapours, electrochemical activity of sulphide-containing corrosion products of bright nickel coatings. Methods. Potentiodynamic and cyclic volt-amperometry have been used to study the electrochemical activity of galvanic nickel deposits and their corrosion products. The corrosion rate of galvanic nickel deposits has been determined by gravimetric method. Investigation of surface morphology and composition of galvanic deposits were performed using scanning electron microscopy and X-ray fluorescence analysis. Results.The increased electrochemical activity of sulphide corrosion products of bright nickel coatings is evidenced by an order of magnitude higher cathodic current densities of CVA curves obtained in acetate buffer solutions, in comparison with bright and matte nickel galvanic deposits. It has been shown that at the deposition of sulphide corrosion products of bright nickel coatings on matte nickel foil the corrosion rate of last one increase at the exposition in concentrated acetic acid and its vapours. Conclusions. Significant intensifying effect of sulphur on the corrosion of galvanic nickel deposits in concentrated acetic acid and its vapours has been established. In particular, this can be explained by the decomposition of nickel sulphide (which incorporates in the coating) in acetic acid. Sulphur in the oxidation state (-2) interacts with passive oxide coatings to form an adsorbed monolayer, which leads to the transition of nickel to the active state. Further research will focus on a deeper study of the electrochemical properties of corrosion products of bright nickel coatings.

(IrOx – Pt)/Ti bifunctional electrodes for oxygen evolution and reduction

Mixed Ir–Pt electrocatalytic films on Ti metal supports were prepared via a galvanic deposition process. Two types of (Ir – Pt)/Ti electrodes were prepared with different Ir–Pt compositions (Ir/Pt atomic composition ratios of 1.74 and 0.44, based on ICP-MS measurements) and of a similar total metal loading (0.15 and 0.12 mg cm−2). The simultaneous deposition of both metallic Ir and Pt occurred spontaneously upon immersion of a freshly etched Ti metal substrate into a composite solution of Ir(IV) and Pt(IV) complexes of variable concentration. This was followed by electrochemical anodization to convert Ir to IrOx. Both electrodes showed homogeneous Ir and Pt dispersion on the Ti surface. The bifunctional electrocatalytic performance of (IrOx/Ir – Pt)/Ti electrodes has been tested towards the oxygen evolution (OER) and reduction (ORR) reactions in acidic solutions. The thus prepared Ti-supported Ir–Pt film electrodes exhibited satisfactory performance towards both reactions, with mass-specific currents for OER being higher than those at a single component IrOx/Ir/Ti electrode and the ones for ORR being comparable to those at a single component Pt/Ti electrode.

Composite Coatings of Chitosan and Silver Nanoparticles Obtained by Galvanic Deposition for Orthopedic Implants.

In this work, composite coatings of chitosan and silver nanoparticles were presented as an antibacterial coating for orthopedic implants. Coatings were deposited on AISI 304L using the galvanic deposition method. In galvanic deposition, the difference of the electrochemical redox potential between two metals (the substrate and a sacrificial anode) has the pivotal role in the process. In the coupling of these two metals a spontaneous redox reaction occurs and thus no external power supply is necessary. Using this process, a uniform deposition on the exposed area and a good adherence of the composite coating on the metallic substrate were achieved. Physical-chemical characterizations were carried out to evaluate morphology, chemical composition, and the presence of silver nanoparticles. These characterizations have shown the deposition of coatings with homogenous and porous surface structures with silver nanoparticles incorporated and distributed into the polymeric matrix. Corrosion tests were also carried out in a simulated body fluid at 37 °C in order to simulate the same physiological conditions. Corrosion potential and corrosion current density were obtained from the polarization curves by Tafel extrapolation. The results show an improvement in protection against corrosion phenomena compared to bare AISI 304L. Furthermore, the ability of the coating to release the Ag+ was evaluated in the simulated body fluid at 37 °C and it was found that the release mechanism switches from anomalous to diffusion controlled after 3 h.