Open-circuit Potential Decay Research Articles

Self‐Powered Supercapacitor with Bifunctional Separator in Suppressing Self‐Discharge

AbstractIntegrating energy harvesters with energy storage devices helps enhance energy utilization efficiency. The requirement for external power sources in energy storage devices can also be addressed by the development of an all‐in‐one single system. Vegetable peels can be used as piezoelectric energy harvesters due to the generation of electric dipole within cellulose. The self‐discharge processes cause open circuit potential decay, resulting in a loss of energy stored within the cell. The self‐discharge rate can be controlled by using a piezoelectric separator. This work used garlic skins as a piezoelectric separator, which helped delay the self‐discharge rate. The supercapacitor using Ni−Mn oxide as positive and Fe−Ni sulfide/RGO as negative electrode materials was fabricated with garlic skin as a separator. The device was charged from an initial OCP of ~0.15–~0.37 V in ~ 4 sec by finger tapping. The OCP decay rate was reduced by~88 % compared to that of using the Whatmann separator. The fabricated Ni−Mn oxide RGO/garlic skin/FeS2 RGO exhibited ~72.2 W h kg−1 energy density at a power density of ~2 kW kg−1 in an operated potential window of ~2 V. This research provides a cost‐effective method for developing piezoelectric supercapacitor with low self‐discharge rate.

Open circuit potential decay transients quantify interfacial pH swings during high current density hydrogen electrocatalysis

Open circuit potential decay transients quantify interfacial pH swings during high current density hydrogen electrocatalysis

Formic acid electrooxidation on palladium nanostructured electrodes in concentrated solutions

The formic acid oxidation reaction (FAO) was evaluated on palladium nanostructured films supported on glassy carbon in 0.5 M H2SO4 + x M HCOOH solutions, where 0.5 ≤ x ≤ 8.0, in the potential range 0.2 ≤ Es / V ≤ 0.6 vs. RHE at 25 °C. Measurements consisted in chronoamperometric experiments, which were followed by stripping voltammetry in order to evaluate the presence of COad. Open circuit potential (OCP) decay was also employed to analyse the formic acid spontaneous decomposition. The results of OCP experiments showed the formation of β-PdH hydride as well as the absence of COad for all HCOOH concentrations, evidencing that the spontaneous decomposition of HCOOH on palladium is the dehydrogenation reaction, which produces H2 and CO2. It was demonstrated that COad is not directly involved in the kinetic mechanism of the FAO on palladium, and it was also explained the controversy related to the detection of COad in previous studies. Additionally, the highest FAO electrocatalytic activity was observed at x = 2.0 M

A bacteriorhodopsin-based biohybrid solar cell using carbon-based electrolyte and cathode components

There is currently a high demand for energy production worldwide, mainly producing renewable and sustainable energy. Bio-sensitized solar cells (BSCs) are an excellent option in this field due to their optical and photoelectrical properties developed in recent years. One of the biosensitizers that shows promise in simplicity, stability and quantum efficiency is bacteriorhodopsin (bR), a photoactive, retinal-containing membrane protein. In the present work, we have utilized a mutant of bR, D96N, in a photoanode-sensitized TiO2 solar cell, integrating low-cost, carbon-based components, including a cathode composed of PEDOT (poly(3,4-ethylenedioxythiophene) functionalized with multi-walled carbon nanotubes (CNT) and a hydroquinone/benzoquinone (HQ/BQ) redox electrolyte. The photoanode and cathode were characterized morphologically and chemically (SEM, TEM, and Raman). The electrochemical performance of the bR-BSCs was investigated using linear sweep voltammetry (LSV), open circuit potential decay (VOC), and impedance spectroscopic analysis (EIS). The champion device yielded a current density (JSC) of 1.0 mA/cm2, VOC of −669 mV, a fill factor of ~24 %, and a power conversion efficiency (PCE) of 0.16 %. This bR device is one of the first bio-based solar cells utilizing carbon-based alternatives for the photoanode, cathode, and electrolyte. This may decrease the cost and significantly improve the device's sustainability.

Eliciting the contribution of TiN to photoelectrochemical performance enhancement of Imma-LaTiO2N at neutral pH

The presence of defects, which act as the recombination hubs for photogenerated charge carriers, hinders the improvement of photocatalytic activity for oxygen evolution reaction of LaTiO2N under visible light irradiation via a four-electron-transfer reaction pathway. Here, we involve titanium nitride (TiN) in a varying content (0–17.8%) to improve the efficiency of charge separation and transport, influencing the photoelectrochemical performance of LaTiO2N. The characterization results confirm the formation of a strong contact between orthorhombic-LaTiO2N and cubic-TiN particles. The photoelectrochemical (PEC) measurements reveal the inverse dependence between electron transfer phenomena and charge carrier recombination, which allows to understand the trend when modifying LaTiO2N with TiN. In fact, the incorporation of 17.8% TiN in the LaTiO2N:TiN material results in a higher photocurrent. Open-circuit potential (OCP) decay and transient absorption spectroscopy (TAS) studies confirm longer lifetimes of charge carriers for increasing amounts of TiN in the synthesized materials. Thus, the main role of TiN is to improve the properties of the semiconductor-electrolyte interface, having verified its impact on the separation and transport of photogenerated charge carriers. Furthermore, computational studies predict that the adsorption of water molecules is favored at the LaTiO2N:TiN surface compared to the individual TiN and LaTiO2N surfaces.

Decoration of g-C3N4 by inorganic cluster of polyoxometalate through organic linker strategy for enhancing photoelectrocatalytic performance under visible light

The efficient visible light-driven photoelectrocatalyst (denoted as g-C3N4-CO-TETA-Pr-SiW11) was designed through the organic linker strategy by combination of polyoxometalate (POM) (cluster of [SiW11O39]−8 (SiW11)) with graphitic carbon nitride (g-C3N4). For this purpose, a reactive tetradentate NH2 linker was introduced by oxidation and subsequently amidation reactions on the surface of g-C3N4 frameworks then SiW11 was bonded to the organic linker to generate g-C3N4-CO-TETA-Pr-SiW11. In this study, for the first time, this organic linker strategy was applied for covalent combination of POM and g-C3N4 to design a stable photocatalyst with high-performance. Photoelectrocatalytic performance of prepared catalysts was investigated under visible light irradiation. The photocurrent density of 0.17 mA cm−2 for g-C3N4-CO-TETA-Pr-SiW11 compared with 0.077 mA cm−2 for g-C3N4 was achieved. Investigation of the transient open circuit potential decay and photoluminescence showed the efficient electron-hole separation for g-C3N4-CO-TETA-Pr-SiW11. The arc diameter in Nyquist plots indicated the improved charge transfer and charge carrier's lifetimes after decorating of g-C3N4 with POM. Mott−Schottky plots demonstrated a greater electron transfer at the photo electrode/electrolyte interface for g-C3N4-CO-TETA-Pr-SiW112.8 in compared to g-C3N4. Also, the photoconversion efficiency exhibited more than 2.4 time enhancement for g-C3N4-CO-TETA-Pr-SiW11 photoanode compared to g-C3N4.

Analysis of Decay of Photocatalytic Effect of Titanium Dioxide Electrode

Titanium Dioxide (TiO2) has been studied for its important photocatalytic semiconductor characteristics. Among many applicable areas of TiO2 photocatalysts, we have been studying to use as an anode electrode of the marine wet solar cells or marine microbial fuel cell. These studies include the analysis of TiO2 electrode prepared by the screen-printing method, and also the dye sensitizing effect on TiO2 electrode. In those studies, it was appeared that there is an open circuit potential that shifted to noble direction after TiO2 electrode was irradiated by the light source and measured its electrochemical properties. This phenomenon usually occurred after a few minutes the electrode showed its photocatalytic characteristics. It is unclear which caused the potential loss during the measurement. In this study, we have been trying to understand the mechanism affecting the potential degradation of the TiO2 electrode and the factors affecting that decay.The TiO2 electrodes were prepared by screen printing method. Type 329J4L stainless steel which exhibits duel phase properties was used as a base substrate for the electrode. Firstly, the surface of the substrate was polished and the substrate was cleaned with acetone using the ultrasonic cleaner for 10 minutes. Then, the substrate was passivated with 10% nitric acid (HNO3) solution at 60 ºC for 30 minutes. After that, the substrate was screen printed with TiO2 paste followed by heat treating for 60 minutes and the first layer of TiO2 was formed. For the second layer forming, the substrate was again screen printed with TiO2 paste and heat treated for 30 minutes. With these processes, double-layered heterojunction TiO2 electrode was prepared. The electrode was then coated with insulating epoxy resins and prepared ready for the electrochemical measurements and analysis.The electrochemical measurements of TiO2 electrodes were performed in an artificial seawater used as an electrolyte. The irradiation was carried out on the electrodes using a calibrated Xenon lamp with 150 W (wavelength ranging from 250 nm to 800 nm). The lamp was set to produce an output light intensity of 10.5 mW/cm2. The saturated calomel electrode (SCE) was used as the reference electrode. During the photopotential measurement, the potentials dropped to active direction as the electrodes were exposed to the light irradiation. But the potential values were ennobled rapidly after a few minutes the electrode was irradiated. Preliminary examinations showed that there is a relation between the rebounded potential values (open circuit potential loss) and the heat treatment temperatures of the electrodes. For example, the rebound rate of the electrode with second layer heat treatment temperature of 150 ºC was higher and longer compared to that of the electrode with 550 ºC one. Detailed mechanism was yet under investigation. Those investigation includes the photopotential measurement and the electrochemical impedance spectroscopy (EIS) analysis. The surfaces of the electrodes before and after the measurements of photopotential were compared and observed using the scanning electron microscope (SEM). The X-ray powder diffraction (XRD) analysis and differential thermal analysis (DTA) were also included for analysis of decay mechanism of photocatalytic on the TiO2 electrode. The results of those analyses and the mechanism affecting the open circuit potential decay in the TiO2 electrode will be presented to the upcoming ECS conference meeting.

Revealing and Facilitating the Rate-Determining Step for Efficient Sunlight-Driven Photocatalysis.

Because of the complex composition of the apparent activation energy, the rate-determining step in a photocatalytic reaction like hydrogen evolution is still being explored even after sluggish oxygen evolution is replaced with efficient hole extraction. This issue severely limits the implementation of certain strategies like the synergistic thermal effect. Here, by developing a combined monitor method based on open-circuit potential decay, we demonstrate that semiconductor-cocatalyst interfacial electron transfer occurring on a decisecond to second time scale dominates photocatalytic hydrogen evolution. This time scale is approximately 6-12 orders of magnitude larger than the widely reported values of picoseconds to microseconds and is comparable to that predicted by Durrant et al. To improve photocatalytic hydrogen evolution, we manage to create more intermediate sites by electronically doping the semiconductor surface. This measure promotes semiconductor-cocatalyst interfacial electron transfer by charge recombination and makes the synergistic thermal effect very evident.

Enhanced photoelectrochemical performance of atomic layer deposited Hf-doped ZnO

Generation of hydrogen using photoelectrochemical (PEC) water splitting has attracted researchers for the last two decades. Several materials have been utilized as a photoanode in a water splitting cell, including ZnO due to its abundance, low production cost and suitable electronic structure. Most research attempts focused on doping ZnO to tailor its properties for a specific application. In this work, atomic layer deposition (ALD) was used to precisely dope ZnO with hafnium (Hf) in order to enhance its PEC performance. The resultant doped materials showed a significant improvement in PEC efficiency compared to pristine ZnO, which is linked directly to Hf introduction revealed by detailed optical, structural and electrical analyses. The photocurrent obtained in the best performing Hf-doped sample (0.75 wt% Hf) was roughly threefold higher compared to the undoped ZnO. Electrochemical impedance spectroscopy (EIS) and open-circuit potential-decay (OCPD) measurements confirmed suppression in photocarriers' surface recombination in the doped films, which led to a more efficient PEC water oxidation. The enhanced PEC performance of Hf-doped ZnO and effectiveness of the used metal dopant are credited to the synergistic optimization of chemical composition, which enhanced the electrical, structural including morphological, and optical properties of the final material, making Hf-doping an attractive candidate for novel PEC electrodes.

Inversion of activity in DSSC for TiO2 and ZnO photo-anodes depending on the choice of sensitizer and carrier dynamics

In this study, we have demonstrated an inversion in the efficiency of TiO2 and ZnO based dye sensitized solar cells for an organic sensitizer C343 and another Ru based sensitizer N719. Despite of faster electron injection from sensitizer C343 to TiO2 than ZnO, the later shows a better photovoltaic efficiency. The higher photocurrent in C343-ZnO has been mechanistically justified by slower back electron recombination and higher dye loading obtained from open circuit potential decay, electrochemical impedance spectroscopy and absorption spectra of the sensitized photoanodes. The similar positive features are there for N719-ZnO system also. Still TiO2-N719 performs much better than ZnO-N719 in terms of device efficiency. We have found a signature of H-type aggregate formation of N719 dye on the ZnO photoanode surface which shows a higher energy absorption peak than the monomeric form of the dye in the diffuse reflectance mode absorption spectra of the photoanodes. These type of aggregates are unable to inject electrons into the semiconductor rather the dye aggregates can pull back the electrons from the CB of the ZnO and eventually undergoes ground state recombination. Ultrafast transient absorption spectroscopy and wavelength dependent photo-current spectra provide further insight into the effect of the dye aggregates on the photo-excited carrier dynamics which essentially reduces the light harvesting efficiency.

ZnS@ reduced graphene oxide nanocomposite as an effective sunlight driven photocatalyst for degradation of reactive black 5: A mechanistic approach

Abstract Herein, we report the fabrication of RGO-ZnS nanocomposites by a facile ultrasound assisted hydrothermal process. Three nanocomposites with different weight ratios of RGO namely RGO3-ZnS, RGO5-ZnS and RGO10-ZnS were prepared and characterized by several techniques. The photocatalytic activity of Z nS , the nanocomposites, and P25 was evaluated against Reactive black 5 (RB5) under sunlight irradiation. A high rate constant of 3.05 × 10−2 min−1, the chemical oxygen demand (COD) value of about 10%, and the mineralization efficiency of 90% were obtained within 300 min when RGO3-ZnS was used as a photocatalyst. To elucidate the photocatalytic mechanism of RGO3-ZnS nanocomposite, the reactive oxygen species trapping experiments, photoluminescence, linear sweep voltammetry, and open circuit potential decay measurements were performed. On the basis of the experimental results, the enhanced photocatalytic activities of RGO3-ZnS could be ascribed to the increased dye adsorption, optical absorption and charge carrier generation, efficient separation, and migration of photogenerated charge carriers as well as the decreased recombination probability of electron-hole pairs as a result of introducing of RGO in the nanostructure.

Well-controlled SrTiO3@Mo2C core-shell nanofiber photocatalyst: Boosted photo-generated charge carriers transportation and enhanced catalytic performance for water reduction

In artificial photocatalysis for hydrogen (H2) generation from water reduction, low apparent quantum efficiency (AQE) always confines the photocatalytic conversion efficiency. Here, we demonstrate a new strategy for the design and synthesis of one-dimensional (1D) SrTiO3@Mo2C core-shell nanostructure for highly enhanced photocatalytic H2 generation activity. The thin nanolayer of Mo2C improves the interfacial conductivity, facilitates transport of photo-generated charge carriers as well as prolongs charge carriers’ lifetime, that minimizing the recombination of photo-generated electrons and holes. Thus SrTiO3@Mo2C hybrid achieves drastically enhanced photocatalytic H2 generation rate up to 7.93 mmol h−1 g−1 with respect to the pristine SrTiO3 (0.53 mmol h−1 g−1) in a solar-driven reaction system, with an AQE of 29.3% at 313 nm. The charge carrier dynamics based mechanism was further confirmed by analysis of time-resolved photoluminescence (TRPL), surface photovoltage (SPV), transient photovoltage (TPV), open circuit potential (OCP) decay curves as well as the electrochemical impedance spectroscopy (EIS) measurements. It is unambiguously to demonstrate that Mo2C is a highly active cocatalyst to dramatically boost the charge separation for photocatalytic water reduction.

Panchromatic Sensitizer for Dye-Sensitized Solar Cells: Unsymmetrical Squaraine Dyes Incorporating Benzodithiophene π-Spacer with Alkyl Chains to Extend Conjugation, Control the Dye Assembly on TiO2, and Retard Charge Recombination.

Metal-free near-infrared (NIR) active unsymmetrical squaraine dyes, RSQ1 and RSQ2, with benzodithiophene (BDT) π-spacer and cyanoacrylic acid acceptor were synthesized by utilizing palladium catalyzed direct (hetero)arylation reaction. Methyl and 2-ethylhexyl groups were strategically placed at the BDT unit for RSQ1 and RSQ2, respectively, to investigate the effect of alkylated π-spacer on dye aggregation on the TiO2 surface and recombination reactions at TiO2/dye/electrolyte interface. These dyes have strong absorption (ε > 105 M-1 cm-1) in near-infrared (NIR) region and exhibit similar optical and electrochemical properties as they have same conjugated framework. RSQ2 performed better than RSQ1 owing to its higher open-circuit voltage (Voc) and fill factor (ff) in spite of having comparable short-circuit current density (Jsc). The panchromatic incident photon-to-current conversion efficiency (IPCE) response was also observed for both the dyes. RSQ2 showed power conversion efficiency (PCE) of 6.72% with short-circuit current density (Jsc) of 18.53 mA/cm2, open circuit voltage (Voc) of 0.538 V, and fill factor (ff) of 67.4%, without any coadsorbent. Attenuation of the charge recombination for RSQ2 was revealed by electrochemical impedance analysis (EIS) and open-circuit potential decay transients (OCVD), which attributes to its higher Voc and ff in comparison to RSQ1.

Kinetic Study of the Formic Acid Oxidation on Steady State Using a Flow Cell

The formic acid oxidation (FAO) reaction is studied on platinum in acid solutions using a specially designed flow cell and different experimental techniques, such as open circuit potential decay, chronoamperometry, voltammetric stripping, HCOOH concentration pulses and rotating disc electrode. It allows for the first time the evaluation of the surface coverage of irreversibly adsorbed reaction intermediates on steady state conditions. It is found that the unique species adsorbed irreversibly is CO (E < 0.5 V). It is demonstrated that at higher potentials the adsorption of the intermediate species involved in the FAO is highly reversible and their decomposition is the rate determining step. From the analysis of the results and taken into account available spectroscopic measurements, a new reaction mechanism is proposed, which is compatible with all the known experimental evidences and allows the interpretations of previous unexplained results.

Influence of spontaneous decomposition on the electrochemical formic acid oxidation on a nanostructured palladium electrode

The formic acid electrooxidation reaction was studied in a flow cell in 1M HCOOH–0.5M H2SO4 solution on a palladium film electrode. The evaluation of the open circuit potential (OCP) decay demonstrated that the spontaneous dehydrogenation of formic acid is quickly verified, leading to hydrogen adsorption and absorption. Moreover, the absence of carbon containing adsorbed species was verified by the application of voltammetric stripping after OCP and chronoamperometry. The results obtained demonstrate that the electrocatalytic oxidation of formic acid on Pd takes place through the spontaneous HCOOH dissociative adsorption with CO2 evolution and the adsorbed hydrogen electrooxidation.

Enhanced photocatalytic activity of {1 0 1}-oriented bipyramidal TiO2 agglomerates through interparticle charge transfer

Uniformly packed dense TiO2 bipyramid agglomerates (BPA) with the dominantly exposed {101} facets were designed and synthesized by using a simple solvothermal process. From scanning electron microscopy (SEM) image, BPA consists of uniformly and densely packed nanoparticles forming secondary mesopores. BPA structure was intentionally crushed by ball-milling to obtain c-BPA, the photoactivity of which was compared with BPA. The photocatalytic activities of as-prepared BPA and c-BPA were investigated for hydrogen production and 4-chlorophenol degradation and compared with P25 as a reference TiO2. The BPA showed much higher photocatalytic activities than those of c-BPA and P25 (randomly aggregated commercial TiO2 nanoparticles). The marked efficiency improvement in BPA can be ascribed to the noble nanostructural features: (i) the agglomerated bipyramid (BP) units suppressing the electron-hole recombination through efficient interparticle charge transfer, (ii) the well-developed mesopores allowing the efficient diffusion of reactants and products, (iii) the highly {101}-oriented BP units that help efficient charge separation, and (iv) a good crystallinity of the BP units. These superior properties of BPA were also confirmed in their photoelectrochemical behaviors: the electrode of BPA exhibited the highest photocurrent under UV light, the slowest decay of open-circuit potential after turning off the light, and the lowest charge transfer resistance from the electrochemical impedance spectroscopic (EIS) measurement, which implies the retarded recombination of charge pairs and efficient interparticle charge transfer on BPA. The controlled agglomerated structure of the nano-sized TiO2 can enhance the photocatalytic and photoelectrochemical properties through efficient interparticle charge transfer.

Self-Discharge in Electrochemical Capacitors: A Perspective Article

This perspective article outlines some of the key considerations and literature that have been published on self-discharge in electrochemical capacitors. While for some consumer applications self-discharge is not considered to be a significant issue (e.g. energy storage from regenerative breaking) in applications where the electrochemical capacitor is stored in the charged state for significant times (e.g. coupled with a battery in a cell phone), the impact on energy, power and recharging frequency of both the capacitor and battery can be significant. A description is provided here of the common methods of self-discharge study: half cell vs. full cell measurements and open-circuit potential decay versus float currents. A description of some of the models used to evaluate faradaic self-discharge is presented, with a synopsis of the important aspects of the many available charge redistribution models. An overview of the current self-discharge mechanisms for various ECs is provided, highlighting that for many systems there are significant factors of the self-discharge process which remain unknown. Finally, some future directions are anticipated for the field of self-discharge in electrochemical capacitors.

Self-assembled TiO2 agglomerates hybridized with reduced-graphene oxide: A high-performance hybrid photocatalyst for solar energy conversion

Spherical TiO2 agglomerates incorporated with reduced-graphene oxide (rGO) sheets were fabricated using aerosol assisted self-assembly. Compared to that of conventional graphene–TiO2 composites, the new hybrid geometry of the self-assembled agglomeration of TiO2 and rGO enabled a porous structure, a more efficient charge separation through interconnected TiO2 nanoparticles and rGO, and improved the contact between TiO2 and rGO to maximize the role of rGO as an electron reservoir. The as-prepared rGO–TiO2 composites were characterized with a diverse range of analytical techniques, and their photocatalytic activity was tested in terms of H2 production and gaseous CH3CHO degradation. The incorporation of the rGO sheets into the TiO2 agglomerates promoted the photocatalytic H2 production and CH3CHO oxidation; our results showed that the performance of our systems is directly proportional to the content of rGO (when added up to 10 wt%). This finding confirmed that rGO, acting as an electron collector and mediator, can facilitate charge-pair separation; only a small light-shielding effect by rGO was observed. Furthermore, open-circuit potential decay measurements revealed that the presence of rGO in the agglomerated TiO2 can significantly suppress charge recombination; this further confirmed the role of rGO as an effective electron conduit. The new geometry of the rGO–TiO2 composite proposed in this work shows several advantages compared to various types of graphene–TiO2 composites previously reported, such as the stronger electronic coupling between rGO sheets and TiO2, minimized light-shielding effect by rGO (even when a relatively large amount of rGO is used), and facile scale-up for mass production. Therefore, our rGO–TiO2 composite can be considered as a promising hybrid photocatalyst for solar energy conversion.

An Investigation into the Oxygen Evolution Reaction at Manganese/ Manganese Ruthenium and Ruthenium Oxide Films in Base

Alkaline water electrolysis has been proposed as an environmentally inoffensive route to the production of the large volumes of hydrogen gas required by a possible hydrogen economy [1-5]. In practice, the efficiency of water electrolysis is limited by the large anodic over-potential of the oxygen evolution reaction (OER) [5]. Over the past thirty years, considerable research effort has been devoted to the design, synthesis and characterization of OER anode materials, with the aim of achieving useful rates of active oxygen evolution at the lowest possible over-potential, in order to optimize the overall electrolysis process. Currently, the optimal OER anode materials are Ruthenium and Iridium oxides, since these oxides exhibit the lowest overpotentials for the OER at practical current densities [6]. However, the high cost of these materials compared to other metals and their poor long term stability in alkaline solution renders their widespread commercial utilisation uneconomical [7]. For these reasons, the oxides of the first row transition metals (e.g. manganese, iron, cobalt and nickel) offer a compromise solution. Even though they are not as electrocatalytically active, their relatively low cost and long term corrosion resistance in alkaline solution makes them attractive OER anode materials [7-11].In the present work, we focus on the redox properties and electrocatalytic behaviour with respect to anodic oxygen evolution of manganese and ruthenium oxide electrodes prepared at different molar ratios in aqueous alkaline solution. These films can be prepared simply via thermal decomposition of a metal salt [12]. The structure and morphology of the thermally decomposed oxide materials are examined using thin film XRD, high resolution SEM and FTIR. The redox behavior of the resulting oxide films is investigated as a function of molar ratio and annealing temperature using cyclic voltammetry. The kinetics of the OER at these films has been studied using a range of electrochemical techniques including steady-state polarization and open circuit potential decay curves. In particular, Tafel slopes and reaction orders with respect to hydroxide ion activity are determined. Interestingly, the electrochemical performance for the films is strongly dependent on the molar ratio used, as evident from figure attached. Based on the available kinetic data, a reaction mechanism utilizing the active surfaquo group concept, is proposed. Turnover Frequency numbers are also obtained. Acknowledgements This publication has emanated in part from research conducted with the financial support of Science Foundation Ireland (SFI) under Grant Number SFI/10/IN.1/I2969.

Electrochemical study of the corrosion behaviour of carbon steel in fracturing fluid

Corrosion behaviour of carbon steel (K-55) in fracturing fluid was studied with a rotation cylinder electrode, under static and rotation conditions by means of several electrochemical techniques which are as follows: open circuit potential (OCP) decay, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). The corrosion rate was determined by weight loss measurements. The electrode surface after a prefixed immersion time was characterised by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that carbon steel showed anodic dissolution behaviour that increased under rotating condition. The cathodic polarisation current density also increased with the electrode rotation due to the increased oxygen diffusion on the electrode surface. Two different oxide layers were formed: a dark, thin layer of magnetite tightly adhering to the electrode surface, characterised by localised corrosion spots, and a porous reddish layer of poorly adhering hematite (Fe2O3) and maghemite (γ-Fe2O3). Under higher rotation rate, the developed oxide layer was not so stable, owing to the shear stress induced between the solution and the specimen surface, enhancing the corrosion rate.