Showing papers on "Overpotential published in 2011"
TL;DR: In this article, a large database of HO* and HOO* adsorption energies on oxide surfaces was used to analyze the reaction free energy diagrams of all the oxides in a general way.
Abstract: Trends in electrocatalytic activity of the oxygen evolution reaction (OER) are investigated on the basis of a large database of HO* and HOO* adsorption energies on oxide surfaces. The theoretical overpotential was calculated by applying standard density functional theory in combination with the computational standard hydrogen electrode (SHE) model. We showed that by the discovery of a universal scaling relation between the adsorption energies of HOO* vs HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the oxygen evolution activity, which suggests a fundamental limitation on the maximum oxygen evolution activity of planar oxide catalysts.
2,923 citations
TL;DR: The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are presented to define the obstacles that remain to be surmounted in order to fully exploit the potential of hematite for solar energy conversion.
Abstract: Photoelectrochemical (PEC) cells offer the ability to convert electromagnetic energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Hematite (α-Fe(2)O(3)) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and ample abundance. However, its performance as a water-oxidizing photoanode has been crucially limited by poor optoelectronic properties that lead to both low light harvesting efficiencies and a large requisite overpotential for photoassisted water oxidation. Recently, the application of nanostructuring techniques and advanced interfacial engineering has afforded landmark improvements in the performance of hematite photoanodes. In this review, new insights into the basic material properties, the attractive aspects, and the challenges in using hematite for photoelectrochemical (PEC) water splitting are first examined. Next, recent progress enhancing the photocurrent by precise morphology control and reducing the overpotential with surface treatments are critically detailed and compared. The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are finally presented. These methods help to define the obstacles that remain to be surmounted in order to fully exploit the potential of this promising material for solar energy conversion.
2,318 citations
TL;DR: In this article, an ultra-thin coating of Al2O3 was applied on the surface of high-performance hematite to reduce the overpotential of the material and increase the photocurrent.
Abstract: Hematite is a promising material for inexpensive solar energy conversion viawater splitting but has been limited by the large overpotential (0.5–0.6 V) that must be applied to afford high wateroxidation photocurrent. This has conventionally been addressed by coating it with a catalyst to increase the kinetics of the oxygen evolution reaction. However, surface recombination at trapping states is also thought to be an important factor for the overpotential, and herein we investigate a strategy to passivate trapping states using conformal overlayers applied by atomic layer deposition. While TiO2 overlayers show no beneficial effect, we find that an ultra-thin coating of Al2O3 reduces the overpotential required with state-of-the-art nano-structured photo-anodes by as much as 100 mV and increases the photocurrent by a factor of 3.5 (from 0.24 mA cm−2 to 0.85 mA cm−2) at +1.0 V vs. the reversible hydrogen electrode (RHE) under standard illumination conditions. The subsequent addition of Co2+ ions as a catalyst further decreases the overpotential and leads to a record photocurrent density at 0.9 V vs. RHE (0.42 mA cm−2). A detailed investigation into the effect of the Al2O3 overlayer by electrochemical impedance and photoluminescence spectroscopy reveals a significant change in the surface capacitance and radiative recombination, respectively, which distinguishes the observed overpotential reduction from a catalytic effect and confirms the passivation of surface states. Importantly, this work clearly demonstrates that two distinct loss processes are occurring on the surface of high-performance hematite and suggests a viable route to individually address them.
724 citations
TL;DR: Platinum nanoparticles have long been regarded as the best catalyst for the ORR and are still commonly used in fuel cells due to their relatively low overpotential and high current density with respect to other commercial catalysts, but the kinetics on the Pt-based electrode is sluggish, and the Pt electrocatalyst still suffers from multiple drawbacks.
Abstract: : The oxygen reduction reaction (ORR) is an important process in many fields, including energy conversion (fuel cells, metal air batteries), corrosion, and biosensing. For fuel cells, the cathodic oxygen reduction is a major factor limiting their performance. The ORR can proceed either through a four-electron process to directly combine oxygen with electrons and protons into water as the end product, or a less efficient two-step, two-electron pathway involving the formation of hydroperoxide ions as intermediate. Oxygen reduction also occurs, albeit too slowly to be of any practical significance, in the absence of an ORR catalyst on the cathode. Platinum nanoparticles have long been regarded as the best catalyst for the ORR and are still commonly used in fuel cells due to their relatively low overpotential and high current density with respect to other commercial catalysts. However, the ORR kinetics on the Pt-based electrode is sluggish, and the Pt electrocatalyst still suffers from multiple drawbacks, such as susceptibility to fuel crossover from the anode, deactivation by CO, and poor stability under electrochemical conditions. In addition, the high cost of Pt and its limited natural reserves are the major barriers to mass-market fuel cells for commercial applications.
712 citations
TL;DR: Manganese at work: carbonyl bipyridyl complexes based on manganese, a non-noble abundant and inexpensive metal, have been proved to be excellent molecular catalysts for the selective electrochemical reduction of CO(2) to CO under mild conditions as discussed by the authors.
Abstract: Manganese at work: carbonyl bipyridyl complexes based on manganese, a non-noble abundant and inexpensive metal, have been proved to be excellent molecular catalysts for the selective electrochemical reduction of CO(2) to CO under mild conditions. Another advantage of manganese complexes over rhenium complexes is that these catalysts operate at markedly less overpotential (0.40 V gain).
471 citations
TL;DR: It is demonstrated that the reason LiFePO(4) functions as a cathode at reasonable rate is the availability of a single-phase transformation path at very low overpotential, allowing the system to bypass nucleation and growth of a second phase.
Abstract: Lithium-ion batteries are a key technology for multiple clean energy applications. Their energy and power density is largely determined by the cathode materials, which store Li by incorporation into their crystal structure. Most commercialized cathode materials, such as LiCoO(2) (ref. 1), LiMn(2)O(4) (ref. 2), Li(Ni,Co,Al)O(2) or Li(Ni,Co,Mn)O(2) (ref. 3), form solid solutions over a large concentration range, with occasional weak first-order transitions as a result of ordering of Li or electronic effects. An exception is LiFePO(4), which stores Li through a two-phase transformation between FePO(4) and LiFePO(4) (refs 5-8). Notwithstanding having to overcome extra kinetic barriers, such as nucleation of the second phase and growth through interface motion, the observed rate capability of LiFePO(4) has become remarkably high. In particular, once transport limitations at the electrode level are removed through carbon addition and particle size reduction, the innate rate capability of LiFePO(4) is revealed to be very high. We demonstrate that the reason LiFePO(4) functions as a cathode at reasonable rate is the availability of a single-phase transformation path at very low overpotential, allowing the system to bypass nucleation and growth of a second phase. The Li(x)FePO(4) system is an example where the kinetic transformation path between LiFePO(4) and FePO(4) is fundamentally different from the path deduced from its equilibrium phase diagram.
460 citations
TL;DR: In this article, an electrodeposition process of magnesium metal from Grignard reagent based electrolyte was studied by comparing with lithium, and the results indicated that the dependency of the overpotential on the electrolyte concentration prevent the locally concentrated current resulting to form very uniform deposits.
394 citations
TL;DR: In this article, a set of robust molecular cobalt catalysts for the generation of hydrogen from water is reported, supported by the parent pentadentate polypyridyl ligand PY5Me2.
Abstract: A set of robust molecular cobalt catalysts for the generation of hydrogen from water is reported. The cobalt complex supported by the parent pentadentate polypyridyl ligand PY5Me2 features high stability and activity and 100% Faradaic efficiency for the electrocatalytic production of hydrogen from neutral water, with a turnover number reaching 5.5 × 104 mol of H2 per mole of catalyst with no loss in activity over 60 h. Control experiments establish that simple Co(II) salts, the free PY5Me2 ligand, and an isostructural PY5Me2 complex containing redox-inactive Zn(II) are all ineffective for this reaction. Further experiments demonstrate that the overpotential for H2 evolution can be tuned by systematic substitutions on the ancillary PY5Me2 scaffold, presaging opportunities to further optimize this first-generation platform by molecular design.
366 citations
TL;DR: In this paper, a high surface area electrode is functionalized with cobalt-based oxygen evolving catalysts (Co-OEC), which achieves a current density of 100 mA cm−2 for water oxidation at 442 and 363 mV overpotential, respectively.
Abstract: A high surface area electrode is functionalized with cobalt-based oxygen evolving catalysts (Co-OEC = electrodeposited from pH 7 phosphate, Pi, pH 8.5 methylphosphonate, MePi, and pH 9.2 borate electrolyte, Bi). Co-OEC prepared from MePi and operated in Pi and Bi achieves a current density of 100 mA cm−2 for water oxidation at 442 and 363 mV overpotential, respectively. The catalyst retains activity in near-neutral pH buffered electrolyte in natural waters such as those from the Charles River (Cambridge, MA) and seawater (Woods Hole, MA). The efficacy and ease of operation of anodes functionalized with Co-OEC at appreciable current density together with its ability to operate in near neutral pH buffered natural water sources bodes well for the translation of this catalyst to a viable renewable energy storage technology.
357 citations
TL;DR: Preliminary stability tests in a zero gap cell with an OH(-) conducting membrane show no significant increase in overpotential during 10 days operation in 4 M NaOH electrolyte at a current density of 1 A cm(-2) at 333 K.
Abstract: A number of nickel based materials are investigated as potential oxygen evolution catalysts under conditions close to those met in modern, high current density alkaline water electrolysers. Microelectrodes are used to avoid distortion of voltammetric data by IR drop even at the high current densities employed in such water electrolysers. High surface area nickel metal oxides prepared by cathodic deposition and mixed oxides prepared by thermal methods are considered. A mixed Ni/Fe oxide is the preferred electrocatalyst. The influence of hydroxide ion concentration and temperature on the voltammetry is defined. Preliminary stability tests in a zero gap cell with an OH− conducting membrane show no significant increase in overpotential during 10 days operation in 4 M NaOH electrolyte at a current density of 1 A cm−2 at 333 K.
281 citations
TL;DR: It is shown that enzymes can also be extremely efficient electrocatalysts (catalyststs of redox reactions at electrodes), a consequence of molecular evolution responding to stringent biological drivers for thermodynamic efficiency.
Abstract: Enzymes are long established as extremely efficient catalysts. Here, we show that enzymes can also be extremely efficient electrocatalysts (catalysts of redox reactions at electrodes). Despite being large and electronically insulating through most of their volume, some enzymes, when attached to an electrode, catalyze electrochemical reactions that are otherwise extremely sluggish (even with the best synthetic catalysts) and require a large overpotential to achieve a useful rate. These enzymes produce high electrocatalytic currents, displayed in single bidirectional voltammetric waves that switch direction (between oxidation and reduction) sharply at the equilibrium potential for the substrate redox couple. Notoriously irreversible processes such as CO2 reduction are thereby rendered electrochemically reversible—a consequence of molecular evolution responding to stringent biological drivers for thermodynamic efficiency. Enzymes thus set high standards for the catalysts of future energy technologies.
TL;DR: Nanostructured Si eliminates several critical problems with Si photocathodes and dramatically improves a photoelectrochemical (PEC) reaction important to water-splitting in this article.
Abstract: Nanostructured Si eliminates several critical problems with Si photocathodes and dramatically improves a photoelectrochemical (PEC) reaction important to water-splitting Our nanostructured black Si photocathodes improve the H2 production by providing (1) near-ideal anti-reflection that enables the absorption of most incident light and its conversion to photogenerated electrons and (2) extremely high surface area in direct contact with water that reduces the overpotential needed for the PEC hydrogen half-reaction Application of these advances would significantly improve the solar H2 conversion efficiency of an ideal tandem PEC system Finally, the nanostructured Si surface facilitates bubble evolution and therefore reduces the need for surfactants in the electrolyte
TL;DR: In this article, the surface of Li(Ni1/3Mn 1/3Co/3 Co/3)O2 particles are coated with thin conformal layers of Al2O3 by atomic layer deposition (ALD).
TL;DR: In this paper, the authors investigated the relationship between the current density and the overpotential of anode materials for lithium ion batteries, and showed that there is a significant voltage difference between the charging and discharging profiles even when current density decreases to zero.
TL;DR: In this article, the oxygen evolution reaction (OER) on the low-index surfaces of lithium peroxide was studied and it was shown that the OER processes are kinetically limited by the high energy barrier for the evolution of oxygen molecules.
Abstract: The lithium-air chemistry is an interesting candidate for the next-generation batteries with high specific energy. However, this new battery technology is facing substantial challenges, such as a high overpotential upon charging, poor reversibility, and low power density. Using first-principles calculations, we study the oxygen evolution reaction (OER) on the low-index surfaces of lithium peroxide. The elementary reaction steps and the energy profile of the OER are identified on the low-index surfaces of lithium peroxide. We find that the OER processes are kinetically limited by the high energy barrier for the evolution of oxygen molecules and that the rate of the OER processes is highly dependent on the surface orientation.
TL;DR: A molecular device based on multiwalled carbon nanotubes functionalized by a mononuclear ruthenium catalyst has been shown to split water electrochemically, which constitutes one step forward in the design of artificial photosynthetic systems.
Abstract: A successful team: A molecular device based on multiwalled carbon nanotubes functionalized by a mononuclear ruthenium catalyst has been shown to split water electrochemically (see picture; ITO=indium tin oxide). The readily prepared electrode showed excellent electrocatalytic activity for the oxidation of water, a high current density, and a low overpotential, and constitutes one step forward in the design of artificial photosynthetic systems.
TL;DR: An electrochemically active multiwalled carbon nanotube (MWNT) filter is observed to be effective toward the adsorptive removal and electrochemical oxidation of the aqueous dyes, methylene blue and methyl orange as discussed by the authors.
Abstract: An electrochemically active multiwalled carbon nanotube (MWNT) filter is observed to be effective toward the adsorptive removal and electrochemical oxidation of the aqueous dyes, methylene blue and methyl orange, and the oxidation of the aqueous anions, chloride and iodide. In the absence of electrochemistry, the MWNT filter completely removed all dye from the influent solution until a near monolayer of dye molecules adsorbed to the MWNT filter surface. Electrochemical filtration at 2 V resulted in >98% oxidation of the influent dye during a single pass through the 41 μm thin porous MWNT network with a ≤1.2 s residence time. The electrochemical MWNT filter was also able to oxidize aqueous chloride and iodide with minimal overpotential. However, the oxidation of these anions was limited by the number of electrochemically active MWNT surface sites. These results show the potential of an electrochemical MWNT filter for the adsorptive removal and oxidative degradation of aqueous contaminants.
TL;DR: In this paper, multi-metal catalysts were investigated by depositing platinum group metals on a nickel substrate and showed that Rhodium and nickel proved synergistic to reduce surface blockage and increase catalyst stability.
TL;DR: In this article, the stability of different doped TiO2 systems was analyzed and the scaling relationship between the binding energies of OER intermediates (HOO* versus HO*) was found to follow essentially the same trend as for undoped oxides.
Abstract: The oxygen evolution reaction (OER) on the rutile MTiO2(110) (M=V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Ir, Ni) surfaces was investigated by using density functional theory calculations. The stability of different doped TiO2 systems was analyzed. The scaling relationship between the binding energies of OER intermediates (HOO* versus HO*) is found to follow essentially the same trend as for undoped oxides. Our theoretical analysis shows a lower overpotential associated with OER on the doped MTiO2(110) than on the undoped TiO2(110). The theoretical activity of Cr-, Mo-, Mn-, and Ir-doped TiO2 is found to be close to that of RuO2(110) for some of the configurations in consideration.
TL;DR: Graphene-supported Pt and Pt3M (M = Co and Cr) alloy nanoparticles are prepared by ethylene glycol reduction method and characterized with X-ray diffraction and transmission electron microscopy as discussed by the authors.
DSM1
TL;DR: The results indicate a promising alternative cathode catalyst for ORR in fuel cells, although its performance is still lower (overpotential around 110 mV evaluated by RDE and RRDE) than the reference Pt/C catalyst.
Abstract: One of the major limitations yet to the global implementation of polymer electrolyte membrane fuel cells (PEMFCs) is the cathode catalyst. The development of efficient platinum-free catalysts is the key issue to solve the problem of slow kinetics of the oxygen reduction reaction (ORR) and high cost. We report a promising catalyst for ORR prepared through the annealing treatment under inert conditions of the cobalt–benzotriazole (Co–BTA) complex supported on carbon nanotubes (CNTs). The N-rich benzotriazole precursor was chosen based on its ability to complex Co(II) ions and generate under annealing highly reactive radicals able to tune the physicochemical properties of CNTs. X-Ray photoelectron spectroscopy (XPS) was used to follow the surface structure changes and highlight the active electrocatalytic sites towards the ORR. To achieve further evaluation of the catalysts in acidic medium, voltamperometry, rotating disk electrode (RDE), rotating ring-disk electrode (RRDE) and half-cell measurements were performed. The resulting catalysts (Co/N/CNTs) all show catalytic activity towards the ORR, the most active one resulting from annealing at 700 °C. The overall electron transfer number for the catalyzed ORR was determined to be ∼3.7 with no change upon the catalyst loading, suggesting that the ORR was dominated by a 4e− transfer process. The results indicate a promising alternative cathode catalyst for ORR in fuel cells, although its performance is still lower (overpotential around 110 mV evaluated by RDE and RRDE) than the reference Pt/C catalyst.
01 Nov 2011
TL;DR: In this article, the oxygen evolution reaction (OER) on the low-index surfaces of lithium peroxide was studied and it was shown that the OER processes are kinetically limited by the high energy barrier for the evolution of oxygen molecules.
Abstract: The lithium-air chemistry is an interesting candidate for the next-generation batteries with high specific energy. However, this new battery technology is facing substantial challenges, such as a high overpotential upon charging, poor reversibility, and low power density. Using first-principles calculations, we study the oxygen evolution reaction (OER) on the low-index surfaces of lithium peroxide. The elementary reaction steps and the energy profile of the OER are identified on the low-index surfaces of lithium peroxide. We find that the OER processes are kinetically limited by the high energy barrier for the evolution of oxygen molecules and that the rate of the OER processes is highly dependent on the surface orientation.
TL;DR: In this article, the electrochemical performance of Ni-Yttria stabilised zirconia (Ni-YSZ), Ni-Gd 0.1 Ce 0.9 O 1.95 (Ni−GDC), and Ni/Ruthenium-GDC (Ni/Ru)-GDC hydrogen electrodes and La 0.6 Sr 0.4 Co 0.8 Fe 0.2 MnO 3− δ −YSZ (LSM−YSZ) was investigated.
TL;DR: A mathematical model for all-solid-state Li-ion batteries is presented in this paper, which includes the charge transfer kinetics at the electrode/electrolyte interface, diffusion of lithium in the intercalation electrode, and diffusion and migration of ions in the electrolyte.
Abstract: A mathematical model for all-solid-state Li-ion batteries is presented. The model includes the charge transfer kinetics at the electrode/electrolyte interface, diffusion of lithium in the intercalation electrode, and diffusion and migration of ions in the electrolyte. The model has been applied to the experimental data taken from a 10 Ah planar thin-film all-solid-state Li-ion battery, produced by radio frequency magnetron sputtering. This battery consists of a 320 nm thick polycrystalline LiCoO2 cathode and a metallic Li anode separated by 1.5 mL i3PO4 solid-state electrolyte. Such thin-film batteries are nowadays often employed as power sources for various types of autonomous devices, including wireless sensor nodes and medical implants. Mathematical modeling is an important tool to describe the performance of these batteries in these applications. The model predictions agree well with the galvanostatically measured voltage profiles. The simulations show that the transport limitations in the solid-state electrolyte are considerable and amounts to at least half of the total overpotential. This contribution becomes even larger when the current density reaches 0.5 mA cm 2 or higher. It is concluded from the simulations that significant concentration
TL;DR: In this article, a stationary, isothermal, three-dimensional model for negative half cell of the vanadium redox flow battery is developed, which is based on the comprehensive conservation laws, such as charge, mass and momentum, together with a kinetic model for reaction involving vanadium species.
TL;DR: In this article, the influence of various external impurities, including sulfur, chlorine, phosphorus, boron, and siloxane for anodes, and H 2 O and SO 2 for cathodes, on SOFC performance is compared.
TL;DR: In this article, the authors used steadystate polarization curves and electrochemical impedance spectroscopy (EIS) to determine the surface roughness factor and the intrinsic activities of the catalytic layers of the hydrogen evolution reaction.
TL;DR: In this article, a sensitive hydrogen peroxide (H(2)O(2)) sensor was fabricated based on graphene-Pt (GNPt) nanocomposite, which exhibited a high peak current and low overpotential towards the reduction of H(2), and a wide linear range (2-710 mu M), low limit of detection (0.5 mu M) with a much higher sensitivity than that of Pt nanoparticles or graphene modified electrode.
TL;DR: In this article, two-dimensional nickel hydroxide nanosheets were synthesized by exfoliating surfactant intercalated layered Ni(OH) hydroxides and developed as electrocatalysts for urea electro-oxidation.