Potentiodynamic Conditions Research Articles

Tuning the morphology and chemical distribution of Ag atoms in Au rich nanoparticles using electrochemical dealloying.

Dealloying of Ag-Au alloy nanoparticles (NPs) strongly differs from the corresponding bulk alloy materials. Here, we have investigated the effects of potentiodynamic and potentiostatic dealloying on structure and distribution of residual Ag atoms for Au rich NPs. Two different sizes of Ag rich alloy NPs, 77 ± 26 nm Ag77Au23 and 12 ± 5 nm Ag86Au14, were prepared. 77 nm Ag77Au23 NPs form a homogeneous alloy, while 12 nm Ag86Au14 NPs show an Ag rich shell-Au rich core arrangement. The two groups of as-prepared NPs were dealloyed either under potentiodynamic (0.2-1.3 VRHE) or potentiostatic (0.9, 1.2, and 1.6 VRHE) conditions in 0.1 M HClO4. For the initial 77 nm Ag77Au23 NPs, both dealloying protocols lead to pore evolution. Interestingly, instead of homogenous Ag distribution, numerous Ag rich regions form and locate near the pores and particle edges. The critical dealloying potential also differs by ∼500 mV depending on the dealloying method. The initial 12 nm Ag86Au14 NPs remain dense and solid, but Ag distribution and thickness of the Au passivation layer vary between both dealloying protocols. When the Au passivation layer is very thin, the residual Ag atoms tend to segregate to the particle surface after dealloying. Due to the size effect, small NPs are less electrochemically stable and show a lower critical dealloying potential. In this systematic study, we demonstrate that the mobility of Au surface atoms and dealloying conditions control the structure and residual Ag distribution within dealloyed NPs.

Influence of Anions on the Corrosion Behavior of 9Cr-1Mo Ferritic Steel in Aqueous Media

Modified 9Cr-1Mo steel is used as steam generator material in prototype fast breeder reactors, owing to its good corrosion resistance, creep, and thermal conductivity characteristics. In the present study, the corrosion behavior of modified 9Cr-1Mo steel in aqueous environments containing various corrosive ions at potentiodynamic polarization conditions is reported. In chloride-exposed samples, randomly distributed dense shallow pits were seen, whereas mixed anions (, Cl−, and ) in fresh water resulted in deeper pits uniformly distributed on the entire surface. Laser Raman spectroscopy studies revealed the formation of Fe-oxides/hydroxides and Cr(VI) species, except in alkaline solution. A very thin film of only Fe-oxides (Fe3O4, γ-Fe2O3, and α-Fe2O3) was identified in an OH– ion-dominated solution. X-ray photoelectron spectroscopy results confirm the corroded surfaces comprised of Fe, Cr, and Mo-oxides of varying composition and enrichment of Mo-oxides in alkaline solution. Chloride ions present in the corroded layer influenced the pitting corrosion in neutral chloride and fresh water solutions. Field emission scanning electron microscopy images revealed abundant crystalline lepidocrocite with laminar morphology and doughnut-type magnetite together with pits on the samples exposed in neutral chloride and fresh water media.

Palladium-copper bimetallic surfaces as electrocatalysts for the ethanol oxidation in an alkaline medium

Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticles modified with a sub-monolayer of underpotentially deposited Cu (Cu@Pd/C) and Pd-Cu alloy nanoparticles (Pd-Cu/C), and examined for the ethanol oxidation reaction (EOR) in alkaline solution. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, as well as cyclic voltammetry. As reference catalysts, Pd/C and Pt/C were used. The electrochemically active surface area of all samples was determined from COads and Cuupd desorption and Pd oxide reduction, and used to assess their intrinsic activity for EOR. Intimate contact of Pd with Cu atoms enhanced its activity, regardless of the type of bimetal catalyst. The atomic Pd:Cu ratio between 2:1 and 4:1 appears to be optimal for high activity. The most active catalyst under the potentiodynamic conditions was Cu@Pd/C with θ(Cu) = 0.21,although Pd-Cu/C was superior during the potentiostatic test. All bimetallic catalysts surpassed Pd/C in mass activity. The EOR activity of Pt/C was higher compared to Pd-based catalysts at low potentials, both in terms of specific and mass activity, but with a significant decline over a 30-min potentiostatic stability test.

The use of methanol extract of Rheum Ribes (Işgın) flower as a natural and promising corrosion inhibitor for mild steel protection in 1 M HCl solution

There is a tendency towards natural products with the increase in sensitivity to the environment, people and other living things around the world. In recent years, there has been a similar trend regarding inhibitors used in the metals protection against corrosion. In this study, the adsorption and protection ability of Rheum ribes (RR) flower extract on mild steel (MS) corrosion in 1 M HCl solution were investigated with the help of many electrochemical techniques. The MS surface after exposing to the test solutions was examined by energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and contact angle measurements. Some thermodynamic parameters corresponding to the adsorption of extract molecules on the MS surface and excess surface charge of the steel in the extract containing solution were calculated and a possible mechanism of the corrosion inhibition process was discussed. The durability of the extract film formed on the MS surface was examined under potentiodynamic and potentiostatic conditions. It was found that an adherent and uniformly distributed extract film formed on the MS surface, which is responsible for the inhibition of corrosion. The flower extract provided 94.7 % and 98.4 % protection efficiencies at 1000 ppm concentration after 1 h and 6 h exposure. RR flower extract mitigated both anodic and cathodic reactions, predominantly cathodic process. The extract molecules interact and bond to the MS surface via physical and chemical interactions. The extract could be suggested as a promising natural corrosion inhibitor for MS protection in 1 M HCl solution.

Investigation of adsorption, corrosion inhibition, synergistic inhibition effect and stability studies of Rheum ribes leaf extract on mild steel in 1 M HCl solution

BackgroundDue to high cost, toxicity of conventional inhibitors and environmental regulations, corrosion scientists have directed toward plant extracts as alternatives to conventional inhibitors. In this study, leaf extracts of Rheum ribes (RR leaf) were prepared, and their adsorption and protective effects on mild steel (MS) corrosion were investigated in 1.0 M HCl solution. The synergistic inhibition effect of iodide ions and the stability of surface inhibitor film were also studied. MethodsThe protection ability of extract was investigated using electrochemical techniques. The stability of surface film was evaluated by potentiodynamic and potentiostatic studies. After being exposed to the corrosive medium, the surface of metal was examined using SEM, EDX, AFM and contact angle measurements. Significant FindingsThe extract molecules formed an adherent and homogenous protective film on the MS surface. When the RR leaf extract concentration increased, a stronger inhibition effect against corrosive attack was obtained. At 1000 ppm extract concentration, the protection efficiency of RR leaf extract increased from 91.8% to 94.9% when 1000 ppm KI was added to the inhibited acid solution. The extract molecules adsorbed to the metal surface via physical and chemical interactions. The surface extract film was very stable under potentiostatic or potentiodynamic conditions.

Corrosion Characterization of Friction Stir Weld Dissimilar Aluminium Alloy Joints

The course of contact mix welding is quick acquiring conspicuousness in aviation, marine and car industry because of its benefits as far as mechanical strength, effect and hardness characteristics. There is as yet a requirement for sure fire consideration from the exploration local area to erosion in grating mix welding zones, hence the work introduced here centres around the consumption portrayal of the grinding mix weld divergent aluminium composite. This study looks into friction stir welding under various parametric settings and shows how corrosion happens in a sodium chloride electrolytic media under potentio-dynamic conditions. The friction stir weld joints of dissimilar alloys aluminium are constructed using three sets of parameters. Straight cylinder, taper cylinder, and straight triangular tool profiles; tool rotational speeds of 800, 1000, and 1200 rpm; tool feed rates of 100, 120, and 140 mm/min; and tool offsets of 0.5, 0 mm, and -1.5 mm. The corrosion current (Icorr) reduces as tool rotating speed increases up to 1200 rpm, after which it slightly increases due to the creation of ridges all around the periphery of the friction stir weld area.

Investigation of the Influence of Selected Operating Modes on the Long-Term Stability of Electrocatalysts in the PEM Fuel Cell

The membrane electrode assembly (MEA) is the core component of the fuel cell stack. In it, the conversion of chemical energy into electrical energy takes place at the catalyst layers. The functional capability of the MEA is an indispensable prerequisite for the operation of the fuel cell stack and thus plays a decisive role in defining its stability. In addition to the selection of suitable materials, the mode of operation plays a major role in the durability of the MEA. It is known from the literature that electrochemical degradation reactions generally depend on operating parameters such as temperature, potential and dynamics. [1] Therefore, in order to derive a durability promoting mode of operation for the PEM Fuel Cell as well as to make lifetime predictions, it is necessary to identify and understand the processes occurring during the aging of the MEA.This work deals with the investigation of the influence of the operating parameters in the drive cycle as an important operating mode on the aging of the cathode catalyst layer in the MEA. According to the state of the art, nanoparticulate platinum supported on carbon (Pt/C) is usually used as the cathode catalyst. The degradation of Pt/C has been intensively studied in recent years. Platinum dissolution and Pt agglomeration are discussed as the main causes of Pt/C degradation during PEMFC operation. [2, 3]Studies have shown that the dissolution rate generally increases with potential and can accelerate under potentiodynamic conditions. [1] Dissolution of Pt from the catalyst, transport of Pt ions through the electrode, and precipitation of Pt in the membrane, possibly due to reduction of Pt ions by the H2 crossover from the anode can be associated with the loss of cathode electrochemical surface area (ECSA) and thus irreversible performance loss. [4]The primary objective of this work is to investigate the influence of different operating parameters such as temperature and potential range on the degradation rate of the cathode using an accelerated stress test (AST) which was developed to simulate an analogous to real drive cycle operation of a PEM fuel cell in a vehicle.A secondary objective is to evaluate the AST itself in order to determinate its capability of fuel cell lifetime prediction. For that the transferability of the observed degradation rates are to be evaluated on different integration levels such as single-cell PEM test bench and short-stack multi-cell test bench. As a measure to evaluate the transferability of the accelerated stress tests, the loss of electrochemical active surface area (ECSA) serves as an indirect measure of catalyst degradation and the resulting Pt particle size distribution which is determined by TEM serves as a direct measure. The derivation of acceleration factors for the lifetime tests of the different integration levels would allow an early estimation of the lifetime, this way test time and cost could be significantly saved in the evaluation of new materials.

Polypyrrole/hydrogel hybrid films as multi sensing supercapacitor electrodes

The development of sensing motors (supercapacitors) capable of sensing their surrounding conditions while working through the same two connectivity remains as a great challenge to the scientific world. Polypyrrole/chitosan (PPy/Cs) hybrid film supercapacitors constituted by multistep macromolecular machines - the conducting polymer chains - capable of sensing working electrical, thermal and chemical variables were fabricated. The specific capacitance enhances as the times of coating increase and the fourth coated hybrid film exhibits the best specific capacitance (559 F g−1 at 0.2 A g−1) and cycling stabilities (86 % retained capacitance after 1500 cycles at 2 A g−1). Under galvanostatic conditions, the hybrid film supercapacitors sense or respond to the electrical, thermal and chemical energetic perturbation of the reaction ambient by modifying the consumed electric energy to self-adapt the newly imposed energetic conditions. Under potentiodynamic conditions, the extension of the reaction involving conformational movements of the reacting polymeric chains (coulovoltammetric charges) varies as a double logarithmic function of the working chemical ambient. The sensitivities of the hybrid film supercapacitors concerning the driving current, experimental temperature and electrolyte concentration are improved by an increase in the specific capacitance or the content of polypyrrole. Based on this observation we suggest that any electrochemical device (here, sensing supercapacitors) fabricated using PPy/Cs hybrid films can act as an electrical, thermal and chemical sensor.

Ni(OH)2-Type Nanoparticles Derived from Ni Salen Polymers: Structural Design toward Functional Materials for Improved Electrocatalytic Performance.

Herein, we report the potential-driven electrochemical transformation carried out in basic media of two Ni2+ salen polymers, (poly(NiSalen)s), abbreviated as poly(meso-NiSaldMe) and poly(NiSaltMe). These two polymers, with different configurations of methyl substituents on the imine bridge, were used as precursors for the preparation of electrocatalytically active nickel hydroxide [Ni(OH)2]-type nanoparticles (NPs) anchored in the polymeric matrix as poly[SalenNi(OH)2]. The use of potentiodynamic and potentiostatic electropolymerization conditions for the deposition of polymeric precursors allowed us to control the molecular architecture of poly(NiSalen)s and NPs derived from them. Thus, we obtained different arrangements of NPs embedded in morphologically different poly(Salen) matrixes, indicating their electrocatalytic activity toward ethanol to different extents. Moreover, we found a direct relationship between the electrochemical stability of the poly(NiSalen) precursors operating in the organic solvent-based electrolyte solutions and the easiness of their transformation into Ni(OH)2 NPs operating in the aqueous alkaline media. Poly(NiSalen)s and Ni(OH)2-type NPs were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy.

Brønsted Acid-Functionalized Ionic Co(II) Framework: A Tailored Vessel for Electrocatalytic Oxygen Evolution and Size-Exclusive Optical Speciation of Biothiols.

Metal-organic frameworks (MOFs) not only combine globally demanded renewable energy generation and environmental remediation onto a single platform but also rationalize structure-performance synergies to devise smarter materials with remarkable performance. The robust and non-interpenetrated cationic MOF exemplifies a unique bifunctional scaffold for the efficient electrochemical oxygen evolution reaction (OER) and ultrasensitive monitoring of biohazards. The microporous framework containing Brønsted acid-functionalized [Co2(μ2-OH)(CO2)2] secondary building units (SBUs) exhibits remarkable OER performance in 1 M KOH, requiring 410 mV overpotential to obtain 10 mA cm-2 anodic current density, and a low Tafel slope of 55 mV/dec with 93.1% Faradaic efficiency. Apart from the high turnover frequency and electrochemically assessable surface area, steady OER performance over 500 cycles under potentiodynamic and potentiostatic conditions result in long-term catalyst durability. The highly emissive attribute from nitrogen-rich fluorescent struts benefits the MOF in recyclable and selective fluoro-detection of three biothiols (l-cysteine, homocysteine, and glutathione) in water with a fast response time. In addition to colorimetric monitoring in the solid and solution phases, control experiments validate size-exclusive biothiol speciation through molecular-dimension-mediated pore diffusion. The role of SBUs in the OER mechanism is detailed from density functional theory-derived free energy analysis, which also validates the importance of accessible N-sites in sensing via portraying framework-analyte supramolecular interactions.

Effect of Cationic/Anionic Diffusion Dominated Passive Film Growth on Tribocorrosion

Tribocorrosion behaviours of nickel (Ni) and niobium (Nb) in sodium sulfate (Na2SO4) solution under potentiodynamic and potentiostatic conditions were studied. Under the potentiodynamic condition, the passivation was early broken, accompanied by a sharp increase in frictional coefficient on Nb. The current was more fluctuant, and larger material loss appeared at the higher potential in the potentiostatic condition. However, these phenomena did not occur for Ni, and it even showed lower material loss at the higher potential in the potentiostatic tribocorrosion test. The differences in tribocorrosion behaviour had a close relationship to the passive film growth mechanism, which decided the passive film/metal interface structure. Nb with anionic diffusion dominated mechanism in passive growth would cause the accumulation of oxygen vacancies at the passive film/metal interface. This may weaken the adhesion between the metal and the passive film. However, with the cationic diffusion dominated passive film growth on Ni, cation vacancies concentrated at the passive film/tribo-film interface, and this did not affect the adhesion between metal and passive film. Ni or other passive elements with the cationic diffusion-dominated mechanism in passive film growth were recommended as the alloying element for improving the tribocorrosion resistance of alloys.

Understanding the Electrochemical Dissolution of IrO2 PEM Electrolyzer Anode Catalyst Using Online ICP-MS

The transition to a sustainable society largely relies upon the utilization of renewable energy sources such as solar and wind power.1,2 However, due to their intermittent availability, energy storage and conversion systems such as electrolyzers and fuel cells have become a crucial topic of research and development. Electrocatalysis efforts in low temperature, PEM-based electrolysis tend to focus on the oxygen evolution reaction (OER) since it is several orders of magnitude kinetically slower than its counterpart, the hydrogen evolution reaction (HER). 3 In comparison to other OER catalysts, Ir-based metal oxides (IrOx)4-8 are regarded as the best PEM electrolyzer electrocatalysts as they are both active and, compared to alternatives, such as RE-based oxides, are relatively stable.9,10 However, even Ir-based electrocatalysts slowly undergo dissolution under the operating conditions of the electrolyzer anode. 11-12, 9 Considering the non-renewable and high-cost of Ir, understanding the kinetics and mechanism of its electrochemical dissolution is of vital importance to develop strategies targeting high activity, long-term stability, and limited metal dissolution in acidic media. Mechanistic studies of both OER and dissolution at the solid–liquid interface are more challenging, as they typically require detection of reaction intermediates with short lifetimes. A number of studies have shown possible routes for OER-activated Ir dissolution involve participartion of IrIII, IrIV, and IrV species.13 An electrochemical cell coupled to a highly sensitive analytical technique provides a platform for detection of reaction intermediates and may help to resolve the degradation pathway of Ir and its oxides and the correlation to the OER mechanism.This presentation will outline the dissolution of iridium oxide (IrO2) under various operating conditions. Studies are performed to quantify the amount of dissolved Ir during potentiodynamic conditions in an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution. The electrochemical data combined with the ICP-MS data are used to evaluate the influence of various factors such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits) and catalyst type, on the dissolution processes in acidic electrolytes at room temperature. Fundamental models will be developed to explain the mechanisms of dissolution process under various potential conditions. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the H2NEW Consortium. This work was authored in part by Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357. References N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci., 103, 15729 (2006).V. R. Stamenkovic, D. Strmcnik, P. P. Lopes, N. M. Markovic, Nat. Mater., 16, 57 (2017).S. M. Alia, B. Rasimick, C. Ngo, K. C. Neyerlin, S. S. Kocha, S. Pylypenko, H. Xu, B. S. Pivovar, J. Electrochem. Soc., 163, F3105 (2016).S. M. Alia, M. -A. Ha, G. C. Anderson, C. Ngo, S. Pylypenko, R. E. Larsen, J. Electrochem. Soc., 166, F1243 (2019).S. Cherevko, S. Geiger, O. Kasian, N. Kulyk, J. P. Grote, A. Savan, B. R. Shrestha, S. Merzlikin, B. Breitbach, A. Ludwig, et al., Catal. Today, 262, 170 (2016).Y. Lee, J. Suntivich, K. J. May, E. E. Perry, Y. Shao-Horn, J. Phys. Chem. Lett., 3, 399 (2012).D. F. Abbott, D. Lebedev, K. Waltar, M. Povia, M. Nachtegaal, E. Fabbri, C. Copéret, T. J. Schmidt, Chem. Mater., 28, 6591 (2016).H. N. Nong, T. Reier, H.-S. Oh, M. Gliech, P. Paciok, T. H. T. Vu, D. Teschner, M. Heggen, V. Petkov, R. Schlögl, et al., Nat. Catal. , 1, 841(2018).N. Danilovic, R. Subbaraman, K.-C. Chang, S. H. Chang, Y. J. Kang, J. Snyder, A. P. Paulikas, D. Strmcnik, Y.-T. Kim, and D. Myers, J. Phys.Chem. Lett., 5, 2474 (2014).T. Reier, M. Oezaslan, and P. Strasser, ACS Catalysis, 2, 1765 (2012).S. Cherevko, S. Geiger, O. Kasian, N. Kulyk, J.-P. Grote, A. Savan, B. R. Shrestha, S. Merzlikin, B. Breitbach, A. Ludwig, K. J. J. Mayrhofer, Catal. Today, 262, 170 (2016).O. Kasian, S. Geiger, P. Stock, G. Polymeros, B. Breitbach, A. Savan, A. Ludwig, S. Cherevko, K. J. J. Mayrhofer, J. Electrochem. Soc., 163, F3099 (2016).O. Kasian, J.-P. Grote, S. Geiger, S. Cherevko, and K.J.J. Mayrhofer, Angew. Chem. Int. Ed. , 57, 2488 (2018).

Mixed-​ligand-devised anionic MOF with divergent open Co(II)-nodes as chemo-resistant, bi-functional material for electrochemical water oxidation and mild-condition tandem CO2 fixation

Metal-organic frameworks (MOFs) combine unique merits of heterogeneous and molecular catalysts, where purposeful implantation of task-specific functionalities along the pore structure can promise electrocatalytic oxygen evolution reaction (OER) and cascade chemical valorization of CO2. Although, both these attributes are crucial for renewable energy and environmental remediation, their effective amalgamation over a single platform is hitherto unexplored, yet extremely demanding. The chemically robust, and non-penetrated charged framework CSMCRI-10 (CSMCRI = Central Salt & Marine Chemicals Research Institute) exemplifies activation induced generation of high density Co(II) nodes with diverse open coordination positions along the unidirectional porous channels, and act as unique bi-functional material. Building on the presence of redox-active [Co2(µ2-OH)(COO)4] secondary building units, the activated framework (10a) demonstrates efficient water oxidation in alkaline medium (1 M KOH). The MOF requires only 396 mV overpotential to reach 10 mA/cm2 anodic current density, and possesses a Tafel slope of 102 mV/decade with admirable 95.1% Faradaic efficiency, signifying high rate of oxygen evolution reaction. The OER turn-over frequency is found to be within the range of best reported values (0.03s−1), and the framework stability is preserved in both potentiodynamic and potentiostatic conditions over 500 consecutive cycles. Further, the Lewis acid functionalized 10a benefits solvent-free CO2 conversion to cyclic carbonate in highly synergistic manner with adequate reusability and broad substrate scope. To the best of tandem catalysis, rarest oxidative carboxylation of CO2 and styrene is realized via single-step styrene carbonate synthesis with exceptional conversion under relatively mild reaction condition.

Electrochemical and Theoretical Studies of &lt;i&gt;Inula viscosa&lt;/i&gt; Extract as Green Corrosion Inhibitor for Mild Steel in Hydrochloric Acid Solution

In this employ, we deliberate the effectuality of corroding inhibition of carbon steel API 5 L Gr – B in HCl 1M solution using the n-butanolic extract taken of Inula Viscosa plant. The repressive strength was observed by the electrochemical methods, Videlicet potentiodynamic condition and impedance measurements. The results indicated that the forbiddance efficiency increases with exploding choose attention. A maximum inhibition rate of 92.37 % was recorded at 600 ppm of inhibitor denseness according to the potentiodynamic measurements. The extract seems to be a goodness corroding inhibitor of electrode writing based on the obtained results. The adsorption on the element articulator was instituted to obey to Langmuir isotherm. In expansion, the HOMO and LUMO analyzing were carried out utilizing the useful thickness hypothesis strategy (DFT / B3LYP). Since HOMO and LUMO are the foremost critical orbitals in atoms, they are exceptionally valuable for understanding certain atomic properties. In expansion, from the outcome of the DFT calculations, we obtained as follows: the total dipole moment of the molecule (μ), the absolute hardness (η), the absolute electronic negativity (χ).

Phthalocyanine-cored conductive polymer design: effect of substitution pattern and chalcogen nature on optical and electrical properties of Zn(II)-phthalocyanine–cored polycarbazoles

Phthalocyanines are one of the important candidates of tetrapyrrolic macrocycles having a π-conjugated system, and conductive polymers (CPs) have recently attracted an increasing interest as designing of new molecular materials. A smart combination of these two unique structures can produce materials with the desired properties to design various organic-molecular devices. However, fundamental principles of the design engineering for synthesis of phthalocyanine-cored CP with unique optoelectronic properties has not been investigated yet. For this purpose, tetrasubstituted peripheral or non-peripheral Zn(II)-phthalocyanine containing thioalkyl- or alkoxy-group–linked carbazoles have been synthesized. Electropolymerization of the materials under potentiodynamic conditions yielded a series of analogous donor−acceptor CPs in which the only difference was the nature of the chalcogen (O or S) and substitution pattern (peripheral or non-peripheral) on the phthalocyanine core. This was shown to have a significant impact on the optical and electrochemical properties of the CPs because of the difference in electronegativity of chalcogen and inductive effect of the substitution pattern. Here, a comprehensive investigation of the design of phthalocyanine-cored CP has been concluded to reveal structure–property relationship.

Microstructure and Tribocorrosion Behavior of Al2O3/Al Composite Coatings: Role of Al2O3 Addition

Pure Al coating and Al2O3 particles reinforced Al composite coatings were prepared by arc-spraying. The feedstocks were pure Al wires and Al-based cored wires containing 10, 20, 30 vol.% Al2O3, respectively. The evolutions of microstructure, porosity and microhardness of the coatings with different Al2O3 contents were investigated. Microstructural analysis shows that the addition of Al2O3 particles improves density and decreases the porosity of the coating. The average hardness of the composite coatings varies from 39 to 416.5 HV0.1 as Al2O3 content increases from 0 to 30 vol.%. However, the microhardness of the Al matrix in the coatings increases first and then decreases as a function of Al2O3 contents. The tribocorrosion tests were performed under potentiodynamic polarization conditions in 3.5 wt.% NaCl solution. The cathodic shift of open circuit potential and the increase in current density are induced by sliding wear. Compared with pure Al coating, the Al2O3 particles reinforced composite coatings display a lower wear rate and coefficient of friction. The Al-20 vol.%Al2O3 composite coating shows superior resistance to tribocorrosion. The tribocorrosion mechanism of the composite coatings is delamination coupling of corrosion wear.

Investigation of High Power Impulse Magnetron Sputtering deposited nanoscale CrN/NbN multilayer coating for tribocorrosion resistance

Recycling equipment (waste/sea water/chemicals) need high tribocorrosion resistance. In this work High Power Impulse Magnetron Sputtering technique deposited nanoscale CrN/NbN multilayer coating for tribocorrosion resistance is explored. Sliding-wear experiments were conducted on CrN/NbN coated High Speed Steel (HSS) test coupons with an alumina (Al2O3) ball as a counterpart in a corrosive environment (3.5% NaCl solution) under potentiodynamic and potentiostatic conditions. Results reveal that coated substrates exhibited (by a factor of 3) lower corrosion currents and high tribo-corrosion resistance (Kc = 2 × 10−15 m3N−1m−1) as compared to uncoated HSS specimens. The alumina counterpart exhibited negligible wear in all the tests. Superior adhesion and dense microstructure consisting of flat and well-defined hard nitride nanolayers leads to stable friction coefficients and retain the unique nanoscale layer-by-layer wear mechanism without delamination. Effect of corrosion on friction coefficients, wear mechanisms and vice versa has been presented.

Effect of substituent structure on formation and properties of poly-hydroxyphenyl porphyrin films obtained by superoxide-assisted method

In this work, we have studied electrochemical formation of poly-2H-5,10,15,20-tetrakis (meta-hydroxyphenyl)porphyrin (H2T (3-OHPh)P) and poly-2H-5,10,15,20-tetrakis (para-hydroxyphenyl)porphyrin (H2T (4-OHPh)P) films from solutions in dimethyl sulfoxide in potentiostatic and potentiodynamic conditions. We have found the potential regions and determined the stages of poly-porphyrin film formation. It has been shown that the interaction of hydroxyporphyrin with superoxide anion radical (O2•–) makes a significant contribution to the electrochemical deposition of the films. For the first time, it has been proved that it is possible to form poly-H2T (3-OHPh)P and poly-H2T (4-OHPh)P films in potentiostatic conditions in the region of oxygen reduction potentials. We have also studied precursor structure effects on the formation kinetics of such films, their thickness, surface morphology and physico-chemical characteristics. It has been determined that poly-H2T (3-OHPh)P films whose formation is assisted by O2•– have more pronounced passivating properties than poly-H2T (4-OHPh)P ones formed in the same conditions. It has been shown that applying the discussed deposition method leads to the formation of a polymeric structure in which the C–O–C bridges are the main binding motif of the hydroxyphenylporphyrins in the poly-porphyrin film. In this work, we also discuss the mechanism of polyporphyrin film formation. For the poly-H2T (4-OHPh)P film, we have evaluated the specific resistance (1500 Ohm∗cm) and found the quasi-reversible electrochromic effect opening up a lot of opportunities for practical applications of such films.

Microelectrode Studies of S-NDR Copper Electrodeposition: Potentiodynamic and Galvanodynamic Measurements and Simulations

Copper electrodeposition from a CuSO4—H2SO4 electrolyte containing a polyether suppressor and (0 to 100) μmol∙L−1 Cl− is examined using a 25 μm diameter microdisk electrode. Optical imaging during cyclic voltammetry and galvanodynamic measurements reveal hysteresis, overpotential inversions, and the morphological evolution accompanying breakdown of the polyether-chloride inhibition layer. Simulations involving co-adsorption of the suppressor-halide adlayer and its subsequent breakdown capture the positive feedback and negative differential resistance (S-NDR) evident in electroanalytical measurements as well as important aspects of electrode shape evolution. The impact of electrode shape change on simulations of electroanalytical experiments is quantified in comparison to a stationary interface approximation. For potentiodynamic conditions, adlayer breakdown propagates rapidly from the center of the microelectrode surface although the final deposit profile is non-uniform due to enhanced transport to the disk perimeter. In contrast, galvanodynamic experiments in more concentrated Cl− solutions reveal spatially selective suppressor breakdown with deposition initially localized to the microelectrode center followed by outward expansion as applied current is increased. The difference between potentiodynamic and galvanodynamic responses reflects the convolution of S-NDR critical behavior with the respective control-loop load lines. Microelectrodes constrain or frustrate the otherwise random bifurcation process giving rise to predictable morphologies unattainable on macroscale electrodes.

An electrochemical quartz crystal microbalance study of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization process

The process of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization has been studied by the quartz crystal microbalance method in different electrodeposition conditions. The films were deposited in two modes: in potentiostatic conditions (at the potential of [Formula: see text]2 V) and in potentiodynamic conditions (CV with the potential scan rate of 20 mV/s). The effect of electrolysis parameters on 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization has been studied by obtaining films in two modes and using two supporting electrolytes: tetrabutylammonium perchlorate or tetrabutylammonium hexafluorophosphate. The biggest film mass gain was observed on a clean electrode surface. At further film deposition on the polyporphyrin-coated electrode, the film mass growth stopped. The electrodeposition effectiveness was somewhat higher in the potentiodynamic conditions, with the formation of a looser film. The nature of the supporting electrolyte did not have a significant effect on the electrodeposition process. A significant contribution to the deposition was made by the electrode material. The film thickness was 25–80 nm. The films possessed [Formula: see text]-type conductivity; and the flat-band potential for poly-H[Formula: see text]T(4-OHPh)P obtained in potentiodynamic conditions was 0.33 V, for poly-H[Formula: see text]T(4-OHPh)P obtained in potentiostatic conditions it was 0.16 V.