Electrochemical and Surface Analysis Studies on the Carbon Dioxide Corrosion of X‐65 Carbon Steel

A comprehensive study of the CO₂ corrosion of carbon steel (X‐65) at low partial pressures of CO₂ is reported in this paper. Field emission scanning electron microscopy (FESEM), Raman spectroscopy (RS), synchrotron radiation‐grazing incidence X‐ray diffraction (SR‐GIXRD), and electrode kinetic studies have confirmed that chukanovite, magnetite and siderite are the main corrosion products at low partial pressures of CO₂. Chukanovite forms predominantly in the presence of CO₂, while magnetite was found to be the major corrosion product in the absence of CO₂, although the majority of previous work based on conventional ex‐situ materials characterization techniques has implied that siderite is the main corrosion product. Here, it is shown that the nature of corrosion products is strongly dependent on the experimental conditions at low pressures of CO₂, which has not been elucidated in previous studies. Accordingly, this study has made a significant contribution to identifying the true nature of corrosion scales formed at low partial pressures of CO₂ allowing the development of effective anti‐corrosive agents for the control and prevention of carbon steel corrosion at low CO₂ partial pressures.     

In situ SERS study of the adsorption of inhibitors of carbon dioxide corrosion

A specially designed electrochemical cell incorporating a rotating disc electrode has been used for in situ surface‐enhanced Raman spectroscopy (SERS) studies of the adsorption of inhibitors of carbon dioxide corrosion onto silver‐coated mild steel electrodes. It is shown that SERS‐active inhibitors comprising aromatic moieties may be detected using the SERS technique. Furthermore, the efficacy of adsorption of corrosion inhibitors employed in the present study is optimal near the open cell or corrosion potential, demonstrating that electrode polarization induces electrostatic forces of repulsion that retard the adsorption of the inhibitor to the corroding steel surface. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of low current density electrochemical oxidation on the properties of carbon fiber‐reinforced epoxy resin composites

Changes in surface physicochemical structures of polyacrylonitrile‐based carbon fibers resulted from low current density electrochemical oxidation were monitored by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The relationship between the interlaminar shear strength (ILSS) values of carbon fiber‐reinforced polymers (CFRPs) and carbon fiber surface chemistry including elemental ratios and the relative content of oxygen‐containing functional groups were researched. SEM results revealed that the electrochemical oxidation got rid of surface contaminants generated during the production process. XPS analysis showed that the relative contents of oxygen and nitrogen increased by 446% and 202%, respectively, after the electrochemical oxidation. Carbon fiber surface chemistry was of paramount importance to the interfacial properties of CFRPs. The higher the carbon fiber surface activity, the better the interfacial bonding was, and an increase in the acidic‐group contents was responsible for a higher ILSS value. However, when the current density increased to 1.0 A/m², the interfacial bonding between carbon fiber and the epoxy resin became weak which led to the decline in ILSS values. Copyright © 2012 John Wiley & Sons, Ltd.     

Podlike N‐Doped Carbon Nanotubes Encapsulating FeNi Alloy Nanoparticles: High‐Performance Counter Electrode Materials for Dye‐Sensitized Solar Cells

Podlike nitrogen‐doped carbon nanotubes encapsulating FeNi alloy nanoparticles (Pod(N)‐FeNi) were prepared by the direct pyrolysis of organometallic precursors. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements revealed their excellent electrocatalytic activities in the I^?/I₃^? redox reaction of dye‐sensitized solar cells (DSSCs). This is suggested to arise from the modification of the surface electronic properties of the carbon by the encapsulated metal alloy nanoparticles (NPs). Sequential scanning with EIS and CV further showed the high electrochemical stability of the Pod(N)‐FeNi composite. DSSCs with Pod(N)‐FeNi as the counter electrode (CE) presented a power conversion efficiency of 8.82 %, which is superior to that of the control device with sputtered Pt as the CE. The Pod(N)‐FeNi composite thus shows promise as an environmentally friendly, low‐cost, and highly efficient CE material for DSSCs.     

Electrochemical Monitoring of Saos‐2 Cell Differentiation on Pyrolytic Carbon Electrodes

In this study we establish an electrochemical platform based on two dimensional (2D) pyrolytic carbon electrodes for in vitro analysis of osteoblast differentiation. Electrochemical impedance spectroscopy (EIS) was used to monitor cell adhesion and proliferation, while an electrochemical assay based on square wave voltammetry (SWV) was applied to measure the activity of the differentiation marker alkaline phosphatase (ALP). 2D pyrolytic carbon electrodes were fabricated and used to monitor Saos‐2 cell differentiation for a period of up to 21 days. With this method it was possible to detect a faster increase of ALP activity for cells cultured in medium supplemented with differentiation factors compared to cells cultured in growth medium. This was confirmed by the results obtained with Alizarin Red staining, showing that cells subjected to osteogenic medium went through the entire differentiation process, from proliferation to mineralization. Finally, for the first time, real‐time monitoring of ALP activity combined with continuous EIS monitoring of the same cell culture was achieved using the pyrolytic carbon electrodes.     

Indole‐3‐acetic acid and N‐acetyltryptophan corrosion inhibition effects on mild steel in 1 M hydrochloric acid solution

Corrosion inhibition of indole‐3‐acetic acid and N‐acetyl tryptophan on carbon steel was investigated using polarization and electrochemical impedance spectroscopy (EIS). Polarization results revealed that corrosion inhibitors could reduce the rate of cathodic and anodic reactions on metal surface. EIS analysis showed inhibition efficiency of indoles increases by increasing the inhibitor concentration. The maximum inhibition efficiency was 97% and 80% in solutions containing 10 mM indole‐3‐acetic acid and 10 mM N‐acetyl tryptophan, respectively. The adsorption of inhibitors was found to follow Langmuir isotherm. Adsorption and film formation of inhibitors on the metal substrate were confirmed by calculating thermodynamic adsorption parameter (ΔG⁰_ads) and characterization of exposed metals' surface through contact angle measurements. Copyright © 2014 John Wiley & Sons, Ltd.     

Direct DNA Hybridization on the Single‐Walled Carbon Nanotubes Modified Sensors Detected by Voltammetry and Electrochemical Impedance Spectroscopy

Carboxylic acid functionalized single‐walled carbon nanotubes modified graphite sensors (SWCNT‐PGEs) were developed for electrochemical monitoring of direct DNA hybridization related to specific sequence of Hepatitis B virus, which substantially enhance the electrochemical transduction resulting from guanine oxidation signal comparison to bare PGEs. The performance characteristics of DNA hybridization on disposable CNT‐PGE were explored measuring the guanine signal in terms of optimum analytical conditions; probe and target concentration, hybridization time, and selectivity. The voltammetric results were also complemented with electrochemical impedance spectroscopy (EIS), that was used to characterize the successful construction of carbon nanotubes modification onto the surface of PGEs.     

Highly Efficient CO2 Electroreduction on ZnN4‐based Single‐Atom Catalyst

The electrochemical reduction reaction of carbon dioxide (CO2RR) to carbon monoxide (CO) is the basis for the further synthesis of more complex carbon‐based fuels or attractive feedstock. Single‐atom catalysts have unique electronic and geometric structures with respect to their bulk counterparts, thus exhibiting unexpected catalytic activities. A nitrogen‐anchored Zn single‐atom catalyst is presented for CO formation from CO2RR with high catalytic activity (onset overpotential down to 24 mV), high selectivity (Faradaic efficiency for CO (FE_CO) up to 95 % at ?0.43 V), remarkable durability (>75 h without decay of FE_CO), and large turnover frequency (TOF, up to 9969 h^?1). Further experimental and DFT results indicate that the four‐nitrogen‐anchored Zn single atom (Zn‐N₄) is the main active site for CO2RR with low free energy barrier for the formation of *COOH as the rate‐limiting step.     

Silver‐Catalyzed Three‐Component Coupling of Carbon Dioxide,Amines and α‐Diazoesters

A silver‐catalyzed three‐component coupling reaction of carbon dioxide, amines and α‐diazoesters has been developed for the first time. The novel reaction provides an efficient and practical methodology for the synthesis of a wide range of new α‐carbamoyloxy esters, which are difficult to prepare by existing methods. The advantages of the method include the use of readily available starting materials, simple catalytic system, good atom economy and high functional group tolerance.     

One‐step electrochemical deposition to achieve superhydrophobic cobalt incorporated amorphous carbon‐based film with self‐cleaning and anti‐corrosion

Exploiting a superhydrophobic surface is very significant due to its excellent water repellency which has many practical applications in various fields. In this work, the cobalt incorporated amorphous carbon‐based (Co/a‐C:H) film was prepared successfully on Si substrate via a simple 1‐step electrochemical deposition where electrochemical deposition technology was using cobalt (II) acetylacetonate methanol solution as electrolyte under high voltage, atmospheric pressure, and low temperature. Surprisingly, the as‐prepared film showed a superior superhydrophobic surface with a water contact angle of 153 ± 1° and a sliding angle of 7.6° without any further modification of low surface energy materials. Especially, the tape adhesive, corrosion resistance, and self‐cleaning tests demonstrated that the as‐prepared carbon‐based film could possess fairly well adhesion, superior anti‐corrosion resistance, and self‐cleaning ability, respectively. It indicated that the superhydrophobic Co/a‐C:H film might have potential promising applications in the field of anti‐fouling, anti‐corrosion, and drag resistance, such as the above‐deck structures on icebreaker vessels, ship hulls, and offshore wind turbine blades.     

胆碱与谷氨酸共价单层混合修饰玻碳电极的制作与表征及其测定亚硝酸根的分析应用

A choline and L-glutamic acid mixed monolayer covalently modified glassy carbon electrode (Ch-Glu/GCE) was fabricated and characterized by X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). It provided an excellent example of mixed covalent monolayer modification of carbon electrodes with alkanol and amino acid, and also a facile means for altering the interfacial architecture. The Ch-Glu/GCE displayed good catalytic activity toward the oxidation of nitrite anions. Differential pulse voltammetry was used for determination of nitrite at the Ch-Glu/GCE. The Ch-Glu/GCE showed higher capability for restraint of pollutions than a simple Ch modified electrode or a simple Glu modified electrode.     

Electrochemical Behavior of Dental Ni‐Cr Wirolloy Coated with Eco‐friendly Films in Artificial Saliva

The electrochemical corrosion behavior of the non‐precious Ni‐Cr Wirolloy, being used in dentistry, was investigated before and after applying of two types of eco‐friendly coatings, polyvinyl silsesquioxane (PVS) and nano‐hydroxyapatite (nHAP) separately in artificial saliva solution at 37 °C for 14 d of immersion. The study aimed to investigate the effectiveness of the introduced coating films in enhancing the corrosion resistance of the alloy, and in decreasing the leaching of the toxic Ni ions from the alloy into the environment. The electrochemical corrosion investigation methods used are; open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The evaluated results revealed that the electrochemically coated alloy with PVS. prepared at cathodic potential showed higher corrosion resistance and more stable film compared to that prepared by conventional dip‐coating method. At the same time, the nHAP electrochemically coated film provided the best anti‐corrosion properties over all examined time intervals. The obtained results were confirmed via surface analysis, which assured the formation of the prepared coatings on the alloy surface. Chemical analysis of the corrosion product/solutions showed that the effect of electrochemically deposited nHAP and PVS. polymer films in suppression of Ni ions leaching is similar and slightly higher than that of the chemically coated PVS. one; however, all of them are efficient in decreasing the leaching of the risky Ni ions into the solution.     

Graphene‐Functionalized 3D‐Carbon Fiber Electrodes – Preparation and Electrochemical Characterization

Graphene nanosheets were produced on the surface of carbon fibers by in situ electrochemical procedure including oxidative and reductive steps to yield first graphene oxide, later converted to graphene. The electrode material composed of graphene‐functionalized carbon fibers was characterized by scanning electron microscopy (SEM) and cyclic voltammery demonstrating superior electrochemical kinetics comparing with the original carbon paper. The interfacial electron transfer rate for the reversible redox process of [Fe(CN)₆]^3?/4? was found ca. 4.5‐fold higher after the electrode modification with the graphene nanosheets. The novel electrode material is suggested as a promising conducting interface for bioelectrocatalytic electrodes used in various electrochemical biosensors and biofuel cells, particularly operating in vivo.     

A Simple and Sensitive Poly‐1,5‐Diaminonaphthalene Modified Sensor for the Determination of Sulfamethoxazole in Biological Samples

Sulfamethoxazole (SMZ), an antibacterial sulfonamide drug, has been selectively determined using poly‐1,5‐diaminonaphthalene (p‐DAN) modified glassy carbon electrode (GCE). The modified sensor was characterized by field emission scanning electron microscopy (FE‐SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). SMZ showed linear response in the concentration range of 0.5–150 µM by using square wave voltammetry (SWV) and the detection limit was found to be 0.05 nM with sensitivity of 0.085 µA µM^?1. The proposed sensor has been successfully employed to determine SMZ in the pharmaceutical tablets and human urine samples.     

Application of a 1‐benzyl‐4‐ferrocenyl‐1H‐[1,2,3]‐triazole/carbon nanotube modified glassy carbon electrode for voltammetric determination of hydrazine in water samples

The electrochemical behaviour of hydrazine at a 1‐benzyl‐4‐ferrocenyl‐1H‐[1,2,3]‐triazole‐triazole/carbon nanotube modified glassy carbon electrode has been studied. The modified electrode shows an excellent electrocatalytic activity for the oxidation of hydrazine and accelerates electron transfer rate. The electrocatalytic current increases linearly with hydrazine concentration in the range 0.5–700.0 μm and the detection limit for hydrazine was 33.0 ± 2.0 nm . The diffusion coefficient (D = 2.5 ± 0.1 × 10^?5 cm² s^?1) and kinetic parameters such as the electron transfer coefficient, (α = 0.52) and the heterogeneous rate constant (k′ = 5.5 ± 0.1 × 10^?3 cm s^?1) for hydrazine were determined using electrochemical approaches. Finally, the method was employed for the determination of hydrazine in water samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparative Electrochemical Study of N‐, C‐terminal and Integral Centrin on Adsorption and Metal‐Binding Properties

The adsorption behavior of apo‐ciliate Euplotes octocarinatus centrin (EoCen) and N(C)‐terminal domain of EoCen (N(C)‐EoCen) at a glassy carbon (GC) electrode is studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Interestingly, the adsorption isotherms of C‐EoCen, N‐EoCen and EoCen at a GC surface differ from one another. It is considered to be associated with the different aggregation properties of three proteins. Furthermore, we analyze the metal‐binding properties of centrin and the followed changes in protein structure upon metal‐binding. Corresponding to the four binding sites of EoCen, it shows four no‐equiv signals of CV or EIS change. It indicates that the four different binding sites of EoCen can be discriminated by the EIS titration curves, which is in contrast with conventional use of spectral method. According to the electrostatic potential at the molecular surface of proteins, the favored orientation of N‐EoCen and C‐EoCen on the GC surface is modeled. These models can well explain the results of titration curves of Eu³⁺ to N(C)‐EoCen. This work has established the electrochemical methodology which can be used to measure metal‐binding sites involved and reveal the contribution of each metal site to the whole protein conformational change.     

Highly Catalytic Carbon Nanotube/Pt Nanohybrid‐Based Transparent Counter Electrode for Efficient Dye‐Sensitized Solar Cells

Low‐cost transparent counter electrodes (CEs) for efficient dye‐sensitized solar cells (DSSCs) are prepared by using nanohybrids of carbon nanotube (CNT)‐supported platinum nanoparticles as highly active catalysts. The nanohybrids, synthesized by an ionic‐liquid‐assisted sonochemical method, are directly deposited on either rigid glass or flexible plastic substrates by a facile electrospray method for operation as CEs. Their electrochemical performances are examined by cyclic voltammetry, current density–voltage characteristics, and electrochemical impedance spectroscopy (EIS) measurements. The CNT/Pt hybrid films exhibit high electrocatalytic activity for I^?/I₃^? with a weak dependence on film thickness. A transparent CNT/Pt hybrid CE film about 100 nm thick with a transparency of about 70 % (at 550 nm) can result in a high power conversion efficiency (η) of over 8.5 %, which is comparable to that of pyrolysis platinum‐based DSSCs, but lower cost. Furthermore, DSSC based on flexible CNT/Pt hybrid CE using indium‐doped tin oxide‐coated polyethylene terephthalate as the substrate also exhibits η=8.43 % with J_sc=16.85 mA cm^?2, V_oc=780 mV, and FF=0.64, and this shows great potential in developing highly efficient flexible DSSCs.     

Electrochemical interferometry of a carbon steel in 5–20 ppm KGR-134 inhibited seawater

In the present investigation, holographic interferometry was utilized for the first time to determine the rate change of the number of the fringe evolutions during the corrosion test of a carbon steel in blank seawater and with seawater with different concentrations of a corrosion inhibitor. In other words, the anodic dissolution behaviors (corrosion) of the carbon steel were determined simultaneously by holographic interferometry, an electromagnetic method, and by the electrochemical impedance spectroscopy (EIS), an electronic method. So, the abrupt rate change in the number of the fringe evolutions during corrosion test, EIS, of the carbon steel is called electrochemical interferometry. The corrosion process of the steel samples was carried out in blank seawater and seawater with different concentrations, 5–20 ppm, of KGR-134 corrosion inhibitor using the EIS method, at room temperature. The electrochemical interferograms of the carbon steel in different solutions represent a detail picture of the rate change of the anodic dissolution of the steel throughout the corrosion processes. Furthermore, the optical interferometry data of the carbon steel were compared to the data which were obtained from the EIS tests. Consequently, holographic interferometry is found to be very useful as an electrochemical interferometer for monitoring the anodic dissolution behaviors of metals in aqueous solutions, in which the number of the fringe evolutions of the steel samples can be determined in situ.     

Electrochemical study on corrosion process characteristics of the high-strength low-alloy steels in NaHSO3 solution

Electrochemical methods were used to study the characteristics of corrosion process for the high-strength low-alloy steel and carbon steel used as a huge oil storage tank in NaHSO₃ solution. The polarization curve results show that both steel samples take place in active solution, and the high-strength low-alloy (HSLA) steel has higher i _corr value than carbon steel, which is due to the small grain size that provides high density of active sites for preferential attack. The electrochemical impedance spectroscopy (EIS) results make known that the corrosion process presents two stages. In the first 136 h, one-time constant in EIS diagrams can be shown. Both steels have similar corrosion resistance due to the combination effects of the grain size and microstructure. After 240 h of immersion, a complete passive film forms on the specimen surface, and two-time constants can be shown in EIS diagram. The HSLA steel exhibited improved corrosion resistance when compared with the carbon steel, which is due to the effect of the shape Fe₃C in microstructure and the deposition of FeSO₄ on the electrode surface. The scanning electrode microscopy analyses show that both steels take place in homogenous corrosion, and the carbon steel shows higher surface roughness and many Fe₃C residues. XRD results show that both steels have similar phase constitutes of corrosion products.     

Electrocatalysis of the SiC Particle‐Modified Glassy Carbon Electrode for the Oxidation of Adrenaline

The electrocatalytic properties of the SiC particle‐modified glassy carbon electrode (MGC) for adrenaline oxidation were studied by cyclic voltammetry (CV), double‐potential step chronocoulometry (DPSCC), and electrochemical impedance spectroscopy (EIS) techniques in McIlvaine buffer solution. It was shown that the electrode modified with SiC particles markedly displayed an electrocatalytic effect on the process of the electrochemical reaction of adrenaline, i.e., the activity and the reversibility of the MGC electrode has been significantly improved. This was attributed to the adsorption effect of the electroactive adrenaline molecules on the MGC electrode surface.