Hydrogen Evolution Overpotential Research Articles

Electrochemical Behavior of Fluorinated Boron-Doped Diamond

The surface properties and the electrochem. behavior of a fluorinated B-doped diamond (F-BDD) electrode prepd. by plasma treatment in CF4-He mixt. was studied by XPS and cyclic voltammetry in acidic media. The results showed C-F bonding (C-CF and C-F) on the surface of F-BDD, which made the surface more hydrophobic. Also hydrogen evolution was shifted to more cathodic potentials for fluorinated diamond, as compared with untreated BDD. Finally, the higher cathodic overpotential for hydrogen evolution permitted Ni deposition and nitrate redn. [on SciFinder (R)]

The Effect of Oxygen on Copper Dissolution during Cathodic Polarization

The effect of oxygen on the anomalous dissolution of copper in acidic chloride media is studied. An increase in the copper corrosion rate during cathodic polarization in the potential range from –0.4 to –0.7 V is attributed to stirring of the near-electrode layer by evolving hydrogen bubbles. An addition of surface-active tetrabutylammonium iodide shifts the overpotential of hydrogen evolution and eliminates this effect. The copper dissolution rate during cathodic polarization is shown to be directly proportional to the reduction rate of dissolved oxygen. It is shown experimentally that H2O2 does not affect the dissolution rate of copper during cathodic polarization. The latter fact makes it possible to assume that oxygen reduction stages, which involve hydrogen peroxide, do not affect the anomalous dissolution of copper.

Plasma-sprayed nanocrystalline Ti–Ru–Fe–O coatings for the electrocatalysis of hydrogen evolution reaction

Nanocrystalline Ti–Ru–Fe–O (2-1-1-2) was prepared by mechanical alloying in a ZOZ attritor. Vacuum plasma spray (VPS) was then used to deposit coatings of this material on a substrate. Energy dispersive X-ray fluorescence and X-ray diffraction analysis was used to follow the change in the chemical composition and crystalline structure of the powder upon deposition by VPS. Nanocrystalline Ti–Ru–Fe–O (2-1-1-2) prepared by the ZOZ attritor contains more than 50 wt.% of hexagonal Fe 2Ti and a smaller amount (<10 wt.%) of a cubic phase. Iron contamination coming from the attrition of the milling tools yields [Fe] ∼38 wt.%, almost twice as much as the nominal composition of the powder. When it is used for VPS, reaction between Fe 2Ti and Ru results in the formation of several cubic phases with lattice parameters ranging from 2.96 to 3.02 Å. This reflects a change in the Ru content on the 1 a ( 1 2 , 1 2 , 1 2 ) site of the cubic lattice. The deposition process also results in the formation of Ti 2O 3. This phase is present in excess at the surface of the coating but can be efficiently dissolved through etching in an acid solution. The cathodic overpotential for hydrogen evolution of such activated coatings in typical chlorate electrolysis conditions is η 250=−550 mV.

The Behavior of Oxygen Transport in Valve-Regulated Lead-Acid Batteries with Absorptive Glass Mat Separator

In the oxygen cycle of valve-regulated lead-acid (VRLA) batteries, there are two ways in which oxygen can move from the positive to the negative plates, namely, either horizontally to penetrate the absorptive glass mat (AGM) separator, and/or transport vertically via the gas space. It is found that the oxygen transport depends on the passageway with big void space in the AGM separator and its rate is proportional to the oxygen partial pressure. The rate constant of vertical transport is about three orders higher than that of horizontal transport because of the large void space between the AGM separator and plates. However, in the horizontal direction, the area is very large and the transport path is very short. So the way and the rate of oxygen transport actually depend on the level of saturation in VRLA batteries. The horizontal transport is dominant when the saturation is less than 93%, while the vertical transport becomes dominant when it is higher than 93%. The experiments also indicate that with decreasing saturation, the recombination of more oxygen at the negative plate may oxidize more active atoms and therefore, the overpotential of hydrogen evolution increases obviously. © 2001 The Electrochemical Society. All rights reserved.

Electrochemical Activity of Nanocrystalline Coating of Ti-Ru-Fe-O

Large quantities of nanocrystalline Ti-Ru-Fe-O (2-1-1-2) powder were prepared in a ZOZ attritor. The powder thus obtained contains more than 50 wt.% of hexagonal Ru and Fe 2 Ti. When used as starting material for plasma spray deposition, these phases react together to form B2 cubic structures with various lattice parameters, reflecting change in the stoichiometries. The coating obtained by plasma spraying this powder is adherent on a Fe subtrate. It exhibits a cathodic overpotential for hydrogen evolution (i = -250 mA cm -2 ) in typical chlorate electrolysis conditions of η 250 = -550 mV.

Electrodeposition of Ni from a high internal phase emulsion (HIPE) template

Porous Ni coatings on electrodes were produced by electrodeposition from a High Internal Phase Emulsion (HIPE) containing the components of the electroplating bath in the aqueous phase. Electroplating from the low conductivity water-in-oil emulsion is attributed to partial phase separation and the creation of interconnected aqueous domains. The resulting porous deposits have an irregular structure characterised by a variety of features, indicative of high local current densities and Ni ion depletion in the aqueous domains through which the metal is growing. The porous Ni coatings produced from HIPE emulsions by electroplating at 5–500 mA cm −2, showed lower overpotentials for hydrogen evolution than those of deposits produced through the corresponding solid polymer templates (PHIPEs) as well as typical sintered Ni electrodes of similar thickness, while also exhibiting higher surface area utilisation.

Zinc–Nickel Electroplating from Alkaline Electrolytes Containing Amino Compounds

As found from polarization curves, in alkaline solutions, depending on the potential sweep rate, the action of brighteners based on a polymeric tetraalkylammonium salt (PTAS) can decrease or increase the hydrogen evolution overpotential. In the presence of Zn(II) complexes, the inhibiting action of PTAS on the cathodic hydrogen evolution increases. Some PTAS-based brighteners that ensure production of Zn–Ni alloy coatings uniform in thickness and composition from alkaline electrolytes are proposed. The degree of alloying of Zn–Ni coatings can be controlled by modifying the electrolyte with amino compounds.

Kinetics of hydrogen evolution on single crystal bismuth electrodes

Hydrogen evolution reaction on Bi(001) and Bi(111) faces from aqueous HClO4 and acidic LiClO4 solutions are studied. The applicability of the Frumkin theory of slow discharge is tested. The transfer coefficients corrected for the diffuse double layer are found. The hydrogen evolution overpotential is higher for less active basal Bi(111) face, explained by the lower specific adsorption energy of H2O molecules on Bi(111) than on more active Bi(001) face.

MOCVD of Thin Ruthenium Oxide Films: Properties and Growth Kinetics

Conducting thin films of RuO2 were grown on glass by metal–organic chemical vapor deposition (MOCVD) at substrate temperatures down to 623 K. Tris-trifluoroacetylacetonate-rutheniumIII (Ru(tfa)3) served as the precursor. Film properties, such as resistivity, were improved by the addition of water to the reaction gas. The films were investigated by X-ray diffraction (XRD) and four-probe resistivity measurements. The growth mechanism was studied by in situ ellipsometry, and a model reaction mechanism is proposed. The electrochemical characterization by cyclic voltammetry revealed very small overpotentials for both hydrogen and oxygen evolution. The properties of the films, in particular the resistivity (ρ as low as 72 μΩ cm), are comparable to CVD and sputtered films deposited at much higher temperatures.

Electrochemistry of Macrocyclic Cobalt(III/II) Hexaamines: Electrocatalytic Hydrogen Evolution in Aqueous Solution.

The macrocyclic cobalt hexaamines [Co(trans-diammac)](3+) and [Co(cis-diammac)](3+) (diammac = 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine) are capable of reducing the overpotential for hydrogen evolution on a mercury cathode in aqueous solution. Protons are reduced in a catalytic process involving reoxidation of the Co(II) species to its parent Co(III) complex. The cycle is robust at neutral pH with no decomposition of catalyst. The stability of the [Co(trans-diammac)](2+) and [Co(cis-diammac)](2+) complexes depends on the pH of the solution and the coordinating properties of the supporting electrolyte. Electrochemical studies indicate that the adsorbed Co(II) complex on the surface of mercury is the active catalyst for the reduction of protons to dihydrogen.

Role of Atomic Scale Roughness in Hot Electron Chemistry

As already reported, the hydrogen evolution from neutral pH aqueous electrolytes by hot electrons in Al/Al2O3/Ag junctions at the silver/electrolyte interface is observed only when the silver electrode is weakly “activated” (roughened). After a short description of all relevant phenomena we present a simple model which is based on the increase of the average penetration depth of the hot electrons into the electrochemical double layer by scattering at the surface roughness of the silver(111) face. This leads to a more anodic onset of the hydrogen evolution from the dissociation of water, but only at an activated surface. The model also explains why activation does not reduce the overpotential of the normal hydrogen evolution.

Influence of silver on electrochemical and corrosion behaviours of Pb–Ca–Sn–Al grid alloys Part I: Potentiodynamic and potentiostatic studies

The influence of silver, in the range of 0.02 wt% to 0.07 wt%, on the electrochemical and corrosion properties of Pb–Ca–Sn–Al grid alloy in sulphuric acid solutions at room temperature was investigated by potentiodynamic and potentiostatic methods. The introduction of Ag into a common grid alloy of Pb–Ca–Sn–Al confers some important features on the alloy. Potentiodynamic anodic polarisation measurements provided a qualitative overview of the activating, passivating and transpassivating processes which correspond to Pb → PbSO4, PbSO4 → PbO2 reactions respectively. Cyclic voltammetric measurements provided information on the effect of Ag on the oxidation of PbSO4 to PbO2. The addition of Ag refined the grains and enhanced the passivation of the electrode and its corrosion resistance. A decrease in the oxygen evolution overpotential and an increase in the hydrogen evolution overpotential with the additions of Ag were also observed during the experiments.

Large specific surface area nanocrystalline Ti-Ru-Fe cathode materials for sodium chlorate

Ball-milled nanocrystalline Ti3RuFe powders were mixed with 1, 2, 4, 10 and 20 equivalents of Al and the mixtures were milled again for 20 h. The amount of Al atoms dissolved into the B2 structure of Ti3RuFe does not exceed 8–9 at %, the remaining being present as elemental Al into the powder mixture. During a subsequent treatment of the composite powder in alkaline solutions, the elemental Al is leached out, while Al solutes in the B2 structure are not affected. An examination of the surface by scanning electron microscopy reveals that the leached powder has a highly porous surface structure. Surface area measurements performed by BET measurements show that there is a tenfold increase in the effective surface area. Activated electrodes made from these porous materials show a significant decrease of the cathodic overpotential for hydrogen evolution in typical chlorate electrolysis conditions of about 80 mV.

Electrodeposition of Se on Ti Impedance and photoelectrochemical study of passivation phenomena

Abstract The passivation phenomena observed during electrodeposition of Se on Ti substrates have been investigated. A high overpotential for hydrogen evolution appears essential to observation of passive and transpassive domains. Impedance analysis suggests that passivation results from the formation of a thin, highly resistive film, detected under all conditions of current density, temperature, illumination and concentration of sodium n -dodecyl sulphate. Electron transport in this film presumably occurs by a high field conduction mechanism. The deposits show photoconductive properties typical of amorphous Se.

Smooth Raney nickel coatings for cathodic hydrogen evolution by chemical gas phase reaction of nickel electrode surfaces

Two different processes to prepare smooth* Raney nickel coatings are investigated. Both are based on preparing a precursor coating by gas-phase reaction of nickel at temperatures of around 400°C. Sherardizing of nickel electrodes, that is, reaction with zinc vapour, leads to formation of the γ-phase of Ni–Zn alloy with the approximate composition of 75 to 85wt% Zn (balance: Ni), and gas-phase sulfidizing of nickel electrodes with hydrogen sulfide produces nickel sulfide coatings composed of the phases Ni3S2, αNi7S6 and αNiS. Both types of coating are transformed in situ, the first by caustic leaching and the second during cathodic hydrogen evolution by relatively slow cathodic reduction into smooth, almost closed nanoporous Raney nickel coatings. The comparison of the catalysts from the two different methods reveals the superiority of the second. The hydrogen evolution overpotential is lowest and, during more than 3000h of continuous operation, the catalyst does not deteriorate. Electrodeposited nickel sulfide gives a poorer and less stable RN catalyst than gas phase sulfidized nickel sulfide.

Reduction of carbon dioxide on ruthenium oxide and modified ruthenium oxide electrodes in 0.5 M NaHCO3

Abstract Electrochemical reduction of carbon dioxide is still of great interest in the fields of theoretical and applioed electrochemistry Ruthenium is one of the metals with an intermediate hydrogen evolution overpotential which adsorbs a considerable amount of hydrogen at underpotentials. Therefore, one can expect that the reduction of CO 2 will take place at this electrode at relatively small overpotentials, at which the hydrogen evolution will not be excessive. This will diminish the loss due to concurrent hydrogen evolution. The stability of the electrode surface under vigorous hydrogen evolution enables investigation of the kinetics of CO 2 reduction under long-term potentiostatic conditions. Reduction of CO 2 at ruthenium and ruthenium modified by Cd and Cu adatoms was investigated in 0.5 M NaHCO 3 solutions. Cyclic voltammetry, potentiostatic measurements and long-term electrolysis were performed using standard electrochemical equipment. The analysis of the bulk of the electrolyte was performned with gas chromatography. On the Ru surface as well as on Ru modified by Cu and Cd adatoms and on RuOx + IrOx modified by Cu adatoms and Cd adatoms, CO 2 reduction proceeds to give methanol and acetone during 8 h of holding the potential at −0.8 V. The process of methanol formation on Ru modified by Cu and Cd adatoms is catalyzed by the presence of adatoms and the process of acetone formation is independent of the presence of adatoms at the ruthenium surface. For all the examined surfaces and for further investigations the most promising fact is the relatively low observed overvoltage of the holding potential for CO 2 reduction, at which methanol and acetone were found in the bulk of the electrolyte. The faradiac efficiencies obtained for methanol production in the case of modified ruthenium surfaces indicate some possibility of practical application.

96/06457 An improved equation for the overall heat transfer coefficient in packed beds

In order to inhibit sulfation and hydrogen evolution of the negative plates and to prolong the cycle life of valve-regulated lead-acid batteries for hybrid-electric vehicles, electrochemically active carbon (EAC) and Indium (III) oxide (In2O3) are added into negative active materials of valve-regulated lead-acid batteries. The influences of EAC and In2O3 on the cycle performance of valve-regulated lead-acid batteries are investigated under high-rate partial-state-of-charge conditions. Experiment results indicate that addition of EAC in negative active materials can prolong the high-rate partial-state-of-charge cycle performance of valve-regulated lead-acid batteries, whilst it results in the accelerated evolution rate of hydrogen during charge process. It is also observed that EAC with an appropriate amount of In2O3 can effectively increase the overpotential of hydrogen evolution, which can not only produce the decreased hydrogen evolution rate and promote conversion of PbSO4 to Pb in capacity recovery process, but also prolong the high-rate partial-state-of-charge cycle life of valve-regulated lead-acid batteries. The battery added with 0.5% EAC and 0.02% In2O3 in negative active materials exhibits at least four times longer cycle life than that without In2O3.

96/06127 Lead/acid battery myths

In order to inhibit sulfation and hydrogen evolution of the negative plates and to prolong the cycle life of valve-regulated lead-acid batteries for hybrid-electric vehicles, electrochemically active carbon (EAC) and Indium (III) oxide (In2O3) are added into negative active materials of valve-regulated lead-acid batteries. The influences of EAC and In2O3 on the cycle performance of valve-regulated lead-acid batteries are investigated under high-rate partial-state-of-charge conditions. Experiment results indicate that addition of EAC in negative active materials can prolong the high-rate partial-state-of-charge cycle performance of valve-regulated lead-acid batteries, whilst it results in the accelerated evolution rate of hydrogen during charge process. It is also observed that EAC with an appropriate amount of In2O3 can effectively increase the overpotential of hydrogen evolution, which can not only produce the decreased hydrogen evolution rate and promote conversion of PbSO4 to Pb in capacity recovery process, but also prolong the high-rate partial-state-of-charge cycle life of valve-regulated lead-acid batteries. The battery added with 0.5% EAC and 0.02% In2O3 in negative active materials exhibits at least four times longer cycle life than that without In2O3.

Investigation of the hydrogen evolution reaction at a 10 wt% palladium-dispersed carbon electrode using electrochemical impedance spectroscopy

The hydrogen evolution reaction (h.e.r.) at a 10 wt % palladium-dispersed carbon (Pd/C) electrode in 0.1 m NaOH solution has been investigated with reference to that on carbon (Vulcan XC-72) and palladium foil electrodes by analysing the a.c.-impedance spectra combined with cyclic voltammograms. From the coincidence of the maximum charge transfer resistances and the minimum hydrogen evolution resistances for the h.e.r. at the respective electrode potential for the Pd/C, carbon and Pd foil electrodes, it is suggested that the h.e.r. at the Pd/C electrode takes place along with the absorption and diffusion of hydrogen above −1.10 V vs SCE, whereas the former dominates over the latter below −1.10V vs SCE. In the case of the Pd foil electrode the transition of absorption and diffusion to evolution occurs at −0.96V vs SCE. In contrast to the Pd/C and Pd foil electrodes the h.e.r. occurs strongly at the carbon electrode below −1.20V vs SCE. The hydrogen evolution overpotential on the Pd/C electrode is decreased by 0.10 V in comparison to the carbon electrode due to the larger electrochemical active area of the finely dispersed Pd particles.

アルミナ基板上へのＮｉ‐Ｐ合金皮膜の高電流密度電析

Ni-P alloy film was electrodeposited at 5-232A·dm-2 on an alumina substrate by using the electroplating apparatus equipped with a high flow rate circular pump. With increasing current density, the current efficiency for the deposition on Ni-P decreased once. When the current efficiency was minimum, the P content in the film obtained in the electrolytes with various pH was always 7.5wt%. In the X-ray diffraction profile of Ni-P film with 7.5wt% P content, (200) diffraction peak disappeared and only (111) peak became strong. The overpotential of hydrogen evolution on the Ni-P film with 7.5wt% P content became minimum. The current efficiency, P content, crystal structure and overpotential of hydrogen evolution were closely related one another. TCR of Ni-P alloy film was correlate with its P content.