Showing papers on "Overpotential published in 2008"
TL;DR: In this article, the authors investigated the relative stability of different surface terminations of TiO2 interacting with H2O and analyzed the overpotential needed for the electrolysis and photoelectrolysis of water.
Abstract: The oxidation and photo-oxidation of water on the rutile TiO2(110) surface is investigated using density functional theory (DFT) calculations. We investigate the relative stability of different surface terminations of TiO2 interacting with H2O and analyze the overpotential needed for the electrolysis and photoelectrolysis of water. We found that the most difficult step in the splitting of water process is the reaction of a H2O molecule with a vacancy in the surface to form an adsorbed hydroxyl group (OH*). Comparison to experiment shows that the computed overpotential for O2 evolution (0.78 V) is available under the experimental conditions required for both oxygen and hydrogen evolution.
531 citations
TL;DR: A carbon cathode open to the air is described, on which attached bacteria catalyzed oxygen reduction using electrons provided by the solid-phase cathode, and the strong decrease in activation losses indicates that bacteria function as true catalysts for oxygen reduction.
Abstract: Microbial fuel cells (MFCs) have the potential to combine wastewater treatment efficiency with energetic efficiency. One of the major impediments to MFC implementation is the operation of the cathode compartment, as it employs environmentally unfriendly catalysts such as platinum. As recently shown, bacteria can facilitate sustainable and cost-effective cathode catalysis for nitrate and also oxygen. Here we describe a carbon cathode open to the air, on which attached bacteria catalyzed oxygen reduction. The bacteria present were able to reduce oxygen as the ultimate electron acceptor using electrons provided by the solid-phase cathode. Current densities of up to 2.2 A m(-2) cathode projected surface were obtained (0.303 +/- 0.017 W m(-2), 15 W m(-3) total reactor volume). The cathodic microbial community was dominated by Sphingobacterium, Acinetobacter and Acidovorax sp., according to 16S rRNA gene clone library analysis. Isolates of Sphingobacterium sp. and Acinetobacter sp. were obtained using H-2/O-2 mixtures. Some of the pure culture isolates obtained from the cathode showed an increase in the power output of up to three-fold compared to a non-inoculated control, that is, from 0.015 +/- 0.001 to 0.049 +/- 0.025 W m(-2) cathode projected surface. The strong decrease in activation losses indicates that bacteria function as true catalysts for oxygen reduction. Owing to the high overpotential for non-catalyzed reduction, oxygen is only to a limited extent competitive toward the electron donor, that is, the cathode. Further research to refine the operational parameters and increase the current density by modifying the electrode surface and elucidating the bacterial metabolism is warranted.
276 citations
TL;DR: In this article, a cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution.
254 citations
TL;DR: Solid oxide fuel cells (SOFCs) as mentioned in this paper operate at higher temperatures than solution-based electrolysis cells, which results in a lower Nernst potential, the thermodynamic potential required for water splitting, and in lower electrode overpotentials.
Abstract: When the economy is based on renewable energy resources, such as wind and solar, the major source of H2 for chemical production and energy storage will be from the electrolysis of water. The ability to reduce CO2 efficiently by a similar process could also play a role in reducing greenhouse gas emissions and moving us toward a more sustainable economy. 1 CO produced in this manner could be used in chemical production or reacted with H2 to produce liquid fuels via the Fischer‐Tropsch reaction. 2 Solid oxide electrolyzers SOEs, which are essentially solid oxide fuel cells SOFCs operated in reverse, are capable of higher water electrolysis efficiencies compared to solution-based electrolysis cells because they operate at higher temperatures 925 K. The higher operating temperatures result in a lower Nernst potential, the thermodynamic potential required for water splitting, and in lower electrode overpotentials. 3 The electrode overpotential is the difference between the actual electrode potential and the Nernst potential, and is a measure of the lost efficiency in the cell. SOEs also differ from low-temperature, solution-based electrolyzers in that the electrolyte membrane conducts oxygen anions, rather than protons. The material most often used for the electrolyte is yttria-stabilized zirconia YSZ, a material that is a good oxygen-anion conductor and an electronic insulator. In an SOE, the cathode the fuel-side electrode reaction for water electrolysis is the electrochemical dissociation of steam to produce H2 and O 2 anions, Reaction 1, while recombination of the oxygen ions to O2, Reaction 2, occurs at the anode the air-side electrode H2 O+2 e → O 2 +H 2
205 citations
TL;DR: In this article, a series of Fe42Pt58 nanoparticles of different compositions (x = 63, 58, 54, 42, 15, and 0) were prepared and loaded onto a glassy carbon (GC) electrode where their catalytic activities in the electroreduction of oxygen were examined and compared.
Abstract: FexPt100-x nanoparticles of different compositions (x = 63, 58, 54, 42, 15, and 0) were prepared and loaded onto a glassy carbon (GC) electrode where their catalytic activities in the electroreduction of oxygen were examined and compared. Cyclic and rotating disk voltammetric studies of the resulting FexPt100-x/GC electrodes showed that the catalytic activity for oxygen reduction exhibited a peak-shape dependence on the particle composition (x). Among the series of nanocatalysts under study, Fe42Pt58 particles showed the maximum activity for O2 reduction in terms of the reduction overpotential and current density. This was accounted for by the effects of the Fe content on the electronic structures of the Pt active sites and the resulting Pt−O interactions. Kinetic analyses showed that direct four-electron reduction of adsorbed oxygen occurred on these catalyst surfaces. Additionally, the rate constant of O2 reduction increased with increasing Pt content in the alloy particles; yet, at x ≤ 42, the rate con...
203 citations
TL;DR: In this paper, the morphology of polyaniline nanowires grown electrochemically in anodic aluminum oxide (AAO) templates is strongly influenced by the supporting electrolyte concentration, the potential of electropolymerization, the growth time, and the monomer concentration.
Abstract: The morphology of polyaniline nanowires grown electrochemically in anodic aluminum oxide (AAO) templates is strongly influenced by the supporting electrolyte concentration, the potential of electropolymerization, the growth time, and the monomer concentration. Increasing the sulfuric acid concentration during growth induces a transition from solid nanowires with tubular ends to open nanowires. Current transient data for nanowire growth were interpreted quantitatively in terms of instantaneous and progressive nucleation and growth models, and this analysis was consistent with the observed concentration and potential dependence of nanowire vs nanotube growth. The electrochemical capacitance of nanowire arrays in AAO templates was shown to be related to the morphology of the nanowires. Specific capacitance values in the range of 700 F/g (measured at a charge/discharge rate of 5 A/g) were obtained for porous nanowires grown at 0.5 M aniline concentration at high overpotential in 1.5−2.0 M sulfuric acid solutions.
179 citations
TL;DR: In this paper, the performance of aluminium alloys with small additions of both tin (∼0.1) and gallium (0.05) was investigated. But the results were limited to the case where the gallium distribution was not established.
176 citations
TL;DR: In this paper, the authors compared the performance of the two most used high oxidation power anodes (i.e., anodes with high overpotential for O2 evolution), lead dioxide (PbO2) and boron-doped diamond (BDD), for the electrochemical incineration of solutions containing the herbicide mecoprop (MCPP) by using an electrolytic flow cell.
159 citations
TL;DR: The relationship between mediator-enzyme overpotential and bimolecular rate constant is used to determine the optimum mediator redox potential for maximum power output of a hypothetical biofuel cell with a planar cathode and a reversible hydrogen anode.
Abstract: Oxygen-reducing enzyme electrodes are prepared from laccase of Trametes versicolor and a series of osmium-based redox polymer mediators covering a range of redox potentials from 0.11 to 0.85 V. Experimentally obtained current density generated by the film electrodes is analyzed using a one-dimensional numerical model to obtain kinetic parameters. The bimolecular rate constant for mediation is found to vary with mediator redox potential from 250 s−1 M−1 when mediator and enzyme are close in redox potential to 9.4 × 104 s−1 M−1 when the redox potential difference is large. The value of the bimolecular rate constant for the simultaneously occurring laccase−oxygen reaction is found to be 2.4 × 105 s−1 M−1. The relationship between mediator−enzyme overpotential and bimolecular rate constant is used to determine the optimum mediator redox potential for maximum power output of a hypothetical biofuel cell with a planar cathode and a reversible hydrogen anode. For laccase of T. versicolor (Ee0 = 0.82), the optimum...
154 citations
TL;DR: The cobalt analogue of a highly active nickel electrocatalyst for hydrogen production has been synthesized and characterized as [Co(PPh2NPh2)2(CH3CN)](BF4)2 as discussed by the authors.
Abstract: The cobalt analogue of a highly active nickel electrocatalyst for hydrogen production has been synthesized and characterized as [Co(PPh2NPh2)2(CH3CN)](BF4)2. In the presence of triflic acid in acetonitrile solution, the complex loses one cyclic diphosphine ligand to form [Co(PPh2NPh2)(CH3CN)3](BF4)2, which has been synthesized independently and stucturally characterized. The latter complex serves as an electrocatalyst for hydrogen formation with a turnover frequency of 90 s−1 and an overpotential of 285 mV using bromoanilinium tetrafluoroborate as the acid. A similar cobalt complex with a related diphosphine ligand that does not contain a pendant base is not catalytically active, confirming an important role for the pendant amine in the catalytic reaction.
152 citations
TL;DR: In this paper, a carbon supported Pt-Pd catalyst with a Pt:Pd atomic ratio 77:23 was prepared by reduction of metal precursors with formic acid and characterized by EDX, XRD and XPS techniques.
TL;DR: In this paper, a simple approach combining sonication and sol−gel chemistry was employed to synthesize silica coated carbon nanotube (CNTs) coaxial nanocables.
Abstract: A simple approach combining sonication and sol−gel chemistry was employed to synthesize silica coated carbon nanotube (CNTs) coaxial nanocables. It was found that a homogeneous silica layer can be coated on the surface of the CNTs. This method is simple, rapid, and reproducible. Furthermore, gold nanoparticle supported coaxial nanocables were facilely obtained using amino-functionalized silica as the interlinker. Furthermore, to reduce the cost of Pt in fuel cells, designing a Pt shell on the surface of a noble metal such as gold or silver is necessary. High-density gold/platinum hybrid nanoparticles were located on the surface of 1-D coaxial nanocables with high surface-to-volume ratios. It was found that this hybrid nanomaterial exhibits a high electrocatalytic activity for enhancing oxygen reduction (low overpotential associated with the oxygen reduction reaction and almost four-electron electroreduction of dioxygen to water).
TL;DR: In this paper, a customized gas diffusion layer (GDL) is presented that enhances liquid water transport from the electrode to the gas channels and therefore lowers mass transport losses of oxygen through the porous media.
TL;DR: The electrochemical oxidation of a CO adlayer on Pt[n(111)x(111)] electrodes, with n = 30, 10, and 5, Pt(111), Pt(110) as well as a Pt(553) electrode (with steps of (100) orientation) in alkaline solution has been studied using stripping voltammetry.
Abstract: The electrochemical oxidation of a CO adlayer on Pt[n(111)×(111)] electrodes, with n = 30, 10, and 5, Pt(111), Pt(110) as well as a Pt(553) electrode (with steps of (100) orientation) in alkaline solution (0.1 M NaOH) has been studied using stripping voltammetry. On these electrodes, it is possible to distinguish CO oxidation at four different active oxidation sites on the surface, i.e. sites with (111), (110) and (100) orientation, and kink sites. The least active site for CO oxidation is the (111) terrace site. Steps sites are more active than the (111) terrace sites, the (110) site oxidizing CO at lower potential than the (100) site. The CO oxidation feature with the lowest overpotential (oxidation potential as low as 0.35 V vs. RHE) was ascribed to oxidation of CO at kink sites. The amount of CO oxidized at the active step or kink sites vs. the amount of CO oxidized at the (111) terrace sites depends on the concentration of the active sites and the time given for the terrace-bound CO to reach the active site. By performing CO stripping on the stepped surfaces at different scan rates, the role of CO surface diffusion is probed. The possible role of electronic effects in explaining the unusual activity and dynamics of CO adlayer oxidation in alkaline solution is discussed.
TL;DR: In this paper, the effect of AFL thickness on gas impermeability and performance of a cell was investigated by studying the effect on the open-circuit voltage, ohmic resistance, I-V characteristics and electrode overpotential of cells.
TL;DR: In situ X-ray absorption spectroscopy along with electrochemical measurements (CV and RDE) and previously published EQCN data provide further understanding of the nature of chloride poisoning on different faces/sites of carbon supported platinum clusters (1−2 nm) in acidic medium (HClO4) as discussed by the authors.
Abstract: In situ X-ray absorption spectroscopy along with electrochemical measurements (CV and RDE) and previously published EQCN data provide further understanding of the nature of chloride poisoning on different faces/sites of carbon supported platinum clusters (1−2 nm) in acidic medium (HClO4). Chloride is shown to adsorb in 3-fold sites on the Pt(111) faces at the investigated Cl− concentrations (10−3 and 10−2 M). Atop chloride was found to be present within a narrow potential range (0.4−0.7 V RHE) when compressed adlayers of Cl− are formed on the Pt(111) faces forcing some Cl− to exist in atop/bridged sites. The interplay of anionic (Cl−, Br−, OH−, and HSO4−) adsorption on the different surfaces of Pt are also considered. For example O/OH can easily displace atop chloride on the edges/corners but not the Cl− at the Pt(111) sites, and therefore Cl− dramatically raises the overpotential for water activation at the Pt(111) sites. Chloride also drastically alters the ORR causing an increase of the overpotential b...
TL;DR: In this article, the authors compared three different approaches for describing the cathode catalyst layer of a PEMFC, using a three-dimensional CFD model, including thin-film model, a discrete-catalyst volume model and an agglomerate model.
TL;DR: In this article, a performance analysis of a planar solid oxide fuel cell (SOFC) with different support structures, i.e., electrode (anode and cathode) and electrolyte supports, is presented.
TL;DR: In this article, the structure of thick lead dioxide deposits (approximately 1 mm) formed in conditions likely to be met at the positive electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined.
TL;DR: In this paper, the authors demonstrated the inverse proportionality of activation overpotential with respect to the TPB length in standard composite electrodes such as Ni-yttria-stabilized zirconia YSZ anodes 2,3 and La,SrMnO3 LSM-YSZ cathodes.
Abstract: Solid oxide fuel cells SOFCs are promising to be the nextgeneration energy-conversion devices due to their high efficiency and ultralow pollution emission. 1 Many efforts have been made recently to lower their operating temperatures from conventional 1000°C to 600–800°C, in order to significantly reduce the manufacturing cost and improve the stability of the SOFC system. At a reduced operating temperature, the electrode performance becomes the most important determinant of the overall cell output, especially when a thin-film electrolyte i.e., 5–20 m is applied. The electrode performance is believed to be determined by the sum of various polarizations typically associated with the length of the socalled three-phase boundary TPB where the electronic conductor, ionic conductor, and gases are in contact with each other so that the electrochemical reaction can take place. Therefore, a large TPB length is generally essential for high electrode performance. Several experimental studies demonstrated the inverse proportionality of activation overpotential with respect to the TPB length in standard composite electrodes such as Ni–yttria-stabilized zirconia YSZ anodes 2,3 and La,SrMnO3 LSM–YSZ cathodes. 4,5 A composite electrode is usually composed of an electronic conducting phase, an oxygen-ion conducting phase, and pores for gas transportation. Typical examples of the electronic phases are Ni and LSM, which also serve as the electrocatalyst in the anode and cathode, respectively. The ionic phase is generally an electrolyte material such as YSZ and doped ceria DCO. The TPB length of such a composite electrode is dominantly affected by its microstructure characteristics including particle size, porosity, and distribution state of the electronic and ionic conducting phases. Various electrode models have been established to predict and improve the performance of the composite electrode with regards to its microstructure parameters.
TL;DR: In this article, the authors investigated the effect of surface film formation agent of vinylene carbonate (VC) on charge-discharge cycling efficiency of rechargeable Li-CoO2 cells.
TL;DR: A set of modified PbO 2 anodes doped with the oxides of bismuth and cobalt were prepared by means of electrodeposition in nitrate solutions.
TL;DR: In this paper, the performance of a 6-kW proton exchange membrane (PEM) electrolyzer was modeled using a semi-empirical equation, where the exchange current densities at both the electrodes and the membrane conductivity were the coefficients of the equation.
TL;DR: In this article, a bimetallic catalyst was synthesized via the metallic reductive precipitations of the chloride precursors with NaBH 4 in tetrahydrofuran (THF) at 25 ∘ C.
TL;DR: In this article, the electrochemical behavior of terbium at a tungsten electrode, in the eutectic LiCl-KCl molten was investigated by means of cyclic voltammetry, chronopotentiometry and chronoamperometry.
TL;DR: In this paper, an electrochemical model was developed to study the methane (CH 4 ) fed solid oxide fuel cell (SOFC) using proton conducting electrolyte (H) and SOFC-O, and both internal methane steam reforming (MSR) and water gas shift (WGS) reactions were considered in the model.
TL;DR: In this paper, an electrochemical model was developed to study the ammonia (NH 3 )-fed solid oxide fuel cells with proton-conducting electrolyte (SOFC-H) and oxygen ion conducting electrolyte, which revealed that the actual performance of the NH 3 -fed SOFC- H is considerably lower than the SOFC -O, mainly due to higher ohmic overpotential of the SO FC-H electrolyte.
TL;DR: This sensor shows many advantages such as simple preparation method without using any special electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity at physiological pH values, short response time, long-term stability and remarkable antifouling property toward insulin and its oxidation product.
TL;DR: In this article, the electrodeposition of nickel and nickel-zinc alloys was investigated at polycrystalline tungsten electrode in the zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt.