Electrochemical Oxidation Of Hydrogen Research Articles

Electrochemical Oxidation of Hydrogen on Basal Plane Platinum Electrodes in Imidazolium Ionic Liquids

In this paper, the electrochemical oxidation of hydrogen at the interface between single-crystal platinum electrodes and imidazolium-type room-temperature ionic liquids (RTILs) is studied. This is ...

Pathways of diffusion mixed with subsequent reactions with examples of hydrogen extraction from hydride-forming electrode and oxygen reduction at gas diffusion electrode

This paper covers the role of the rate-determining step (RDS) in anodic hydrogen extraction from hydride-forming electrode. In general, hydrogen extraction from the electrode proceeds through the following steps: (1) hydrogen diffusion within the electrode, (2) hydrogen transfer from absorbed state to adsorbed state, (3) electrochemical oxidation of hydrogen to hydrogen ion involving charge transfer, and (4) hydrogen ion conduction through the electrolyte. In most theoretical and experimental investigations, it has been assumed that the RDS of anodic hydrogen extraction is hydrogen diffusion through the electrode. In real situation, however, the overall rate of hydrogen extraction is simultaneously determined by the rates of two or more reaction steps including hydrogen diffusion. The present work provides the overview of anodic hydrogen extraction in case that diffusion is coupled with interfacial charge transfer, interfacial hydrogen transfer, and hydrogen ion conduction through the electrolyte as well as the purely diffusion-controlled hydrogen extraction. In addition, the mixed controlled diffusion model was also exemplified with oxygen reduction at gas diffusion electrode of fuel cell system.

Modeling the Electrochemical Hydrogen Oxidation and Evolution Reactions on the Basis of Density Functional Theory Calculations

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionModeling the Electrochemical Hydrogen Oxidation and Evolution Reactions on the Basis of Density Functional Theory CalculationsEgill Skúlason, Vladimir Tripkovic, Mårten E. Björketun, Sigrídur Gudmundsdóttir, Gustav Karlberg, Jan Rossmeisl, Thomas Bligaard, Hannes Jónsson, and Jens K. Nørskov*Cite this: J. Phys. Chem. C 2010, 114, 50, 22374Publication Date (Web):November 29, 2010Publication History Published online29 November 2010Published inissue 23 December 2010https://doi.org/10.1021/jp110913nCopyright © 2010 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2938Altmetric-Citations40LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (28 KB) Get e-AlertsSUBJECTS:Density functional theory,Evolution reactions,Hydrogen,Oxidation,Theoretical models Get e-Alerts

ChemInform Abstract: The Self-Discharge of the NiOOH/Ni(OH)2 Electrode. Constant Potential Study.

Hydrogen oxidation currents at a NiOOH/Ni(OH)2 electrode were measured directly at constant potentials for various hydrogen pressures and states of charge. It was found that the hydrogen oxidation current is linearly proportional to the hydrogen pressure at all electrode potentials and that the logarithm of the anodic current is a linear function of electrode potential. It was also found that hydrogen oxidation on the nickel substrate material was strongly inhibited by the presence of nickel hydroxide on the substrate surface. By comparing the currents for hydrogen oxidation and oxygen evolution on the NiOOH/Ni(OH)2 electrode and a nickel substrate, it is suggested that the self-discharge of the NiOOH/Ni(OH)2 electrode is mainly due to electrochemical oxidation of hydrogen on the active electrode material.

CO tolerance and CO oxidation at Pt and Pt–Ru anode catalysts in fuel cell with polybenzimidazole–H 3PO 4 membrane

CO tolerance of H 2–air single cell with phosphoric acid doped polybenzidazole (PA–PBI) membrane was studied in the temperature range 140–180 °C using either dry or humidified fuel. Fuel composition was varied from neat hydrogen to 67% (vol.) H 2–33% CO mixtures. It was found that poisoning by CO of Pt/C and Pt–Ru/C hydrogen oxidation catalysts is mitigated by fuel humidification. Electrochemical hydrogen oxidation at Pt/C and Pt–Ru/C catalysts in the presence of up to 50% CO in dry or humidified H 2–CO mixtures was studied in a cell driven mode at 180 °C. High CO tolerance of Pt/C and Pt–Ru/C catalysts in FC with PA–PBI membrane at 180 °C can be ascribed to combined action of two factors—reduced energy of CO adsorption at high temperature and removal of adsorbed CO from the catalyst surface by oxidation. Rate of electrochemical CO oxidation at Pt/C and Pt–Ru/C catalysts was measured in a cell driven mode in the temperature range 120–180 °C. Electrochemical CO oxidation might proceed via one of the reaction paths—direct electrochemical CO oxidation and water-gas shift reaction at the catalyst surface followed by electrochemical hydrogen oxidation stage. Steady state CO oxidation at Pt–Ru/C catalyst was demonstrated using CO–air single cell with Pt–Ru/C anode. At 180 °C maximum CO–air single cell power density was 17 mW cm −2 at cell voltage U = 0.18 V.

Synthesis, surface chemistry and electrocatalytic properties of oxygen-modified tungsten carbide in relation to the electrochemical hydrogen oxidation

The surface chemistry of tungsten carbide was studied using an indicator spectrophotometric method and X-ray photoelectron emission spectroscopy. The presence of WO2, WO3 and adsorbed polytungstate ions was identified on the surface of WC specimens. The electrocatalytic activity of oxygen-modified tungsten carbide was attributed to the WO2 at their interface with WC. This conclusion is supported by the presence of some density of states of the 5d, 6s electrons at the Fermi level on the W4+ and by the relationship between exchange current density and concentration of the lattice O2−. Insertion of oxygen atoms in the WC crystal lattice leads to a widening of the anodic range of potentials in which the WC maintains its electrochemical activity in hydrogen oxidation reaction.

Electrochemical absorption and oxidation of hydrogen on palladium alloys with platinum, gold and rhodium

Thin layers of Pd and its alloys with Pt, Au and Rh were prepared by electrodeposition on a Au substrate. Hydrogen electrosorption by the obtained electrodes was studied in 0.5 M H(2)SO(4) solution using cyclic voltammetry and chronoamperometry. The influence of the alloying process on selected thermodynamic (the amount of absorbed hydrogen, the stability of the β-phase, the extent of the absorption/desorption hysteresis) and kinetic aspects (the rate of hydrogen absorption and absorbed hydrogen oxidation) of hydrogen absorption and desorption was examined. It was found that the addition of the non-absorbing elements to Pd results in faster kinetics of the hydrogen electrosorption process and a smaller absorption/desorption hysteresis.

Enhancement of electrocatalytic activity of gold nanoparticles by sonochemical treatment

We demonstrate that gold nanoparticles can become catalytically active for the electrochemical hydrogen oxidation reaction by a sonication treatment. Experimental data and theoretical calculations indicate that the activity arises from the supercooled molten state of gold nanoparticles which are enriched with coordinatively unsaturated gold atoms.

Separator-free fuel cell stacks operating in a mixture of hydrogen and air

Fuel cells for vehicular and residential applications have encountered a key technical challenge in cost reduction. This challenge can be avoided by operating a fuel cell stack without the use of gas separators, which are expensive and voluminous and therefore comprise a significant portion of the cost of a fuel cell stack. Single-chamber fuel cells (SCFCs) have the potential of realizing such operation, because there is no need for separation between fuel and air. In this paper, we present a selective anode (PtAu/C) and cathode (Pr-doped Mn2O3/C) for respective electrochemical hydrogen oxidation and oxygen reduction reactions in a SCFC. A single cell with these electrodes operated at 50 °C generated an open-circuit voltage of 1204 mV and a peak power density of 50 mW cm−2 in a feed mixture of 80% hydrogen and 20% air at a flow rate of 30 mL min−1. The high selectivity of these electrodes also enabled the design of two different separator-free fuel cell stacks, parallel and perpendicular to the gas stream. Both cell stacks exhibited increasing stack voltage and power output almost proportionally to the increase in the number of single cells. These results demonstrate that the separator-free fuel cell stack shows high potential for a significant reduction of the cost of fuel cell systems.

Development of a thermodynamically consistent kinetic model for reactions in the solid oxide fuel cell

The parameter estimation using the traditional kinetic modeling of complex reaction systems will give incorrect results if the reaction mechanism contains a loop. In this work, a thermodynamically consistent kinetic model of the anodic electrochemical hydrogen oxidation reaction mechanism of a solid oxide fuel cell (SOFC) is formulated. An iterative algorithm for estimating the reaction rate constants using the thermodynamically consistent model formulation is developed. The kinetic parameters estimated using the proposed method gives a better fit to the experimental data. Using the concept of ‘Degree of rate control’ it is found that the surface reactions may have a greater role in deciding the overall rate. The proposed iterative parameter estimation algorithm developed in this work can also be adapted to other complex chemical and biochemical reaction networks for which the reaction rate constants need to be estimated using the experimental data.

Geometrical Optimization of Double Layer LSM/LSM-YSZ Cathodes by Electrochemical Impedance Spectroscopy

The present-day high-temperature solid oxide fuel cells (SOFCs), based on yttria-stabilized zirconia (YSZ) electrolyte, a lanthanum-strontium manganite (LSM) cathode and a nickel-YSZ cermet anode, operate at 800–1000°C. Cathode materials are restricted to doped lanthanum manganites due to their stability in oxidizing atmosphere, sufficient electrical conductivity, and thermal expansion match to the YSZ electrolyte. Reduction in the operating temperature of SOFCs is desirable to lower the costs and to overcome the technological disadvantages associated with elevated temperatures. However, as the operating temperature is reduced, the decrease in the LSM conductivity and increase in interfacial polarization resistances between the LSM cathode and YSZ electrolyte become critical. Therefore, different approaches have been proposed to improve interfacial quality and electrochemical performance of the LSM/YSZ cathode. The length of the triple-phase boundary (TPB) correlates well with the interfacial resistances to electrochemical oxidation of hydrogen at the anode and reduction in oxygen at the cathode. The extension of the TPB or the number of active reaction sites becomes, therefore, a determining factor in improving electrode performance. This can be achieved by developing electrode materials of higher ambipolar conductivity and by optimizing the microstructure of the electrodes. In order to improve SOFC performance, both composition and structure of the LSM/YSZ interface and of the cathode should be optimized. Recently, functional grade materials (FGMs) were introduced for SOFC technology. However, all studies reported in the literature so far, were focused on cathodes with only compositional gradient. On the other hand, intuitionally the best structure for a functional SOFC should be characterized by both compositional and porosity gradients. Fine grains (and high surface area) close to the electrode/electrolyte surface and large grains (and thus large pore size) at the air/oxygen side are expected to be of advantage. In the present study, “symmetrical” cathode-electrolyte-cathode SOFC single cells were fabricated. The cells consisted of the functional grade LSM cathode with YSZ/LSM cathode functional layer and LSM contact layer. The effects of various geometrical and microstructural parameters of cathode/functional layers on the overall cell performance were systematically investigated. The parameters investigated were the (1) cathode functional layer thickness and grain size and (2) the LSM contact layer thickness. Cathode performances were tested by means of electrochemical impedance spectroscopy (EIS) over a temperature range of 650–950°C, using air as oxidant. The dependence of cell performance on various parameters was rationalized by a comprehensive microscale model. A cathode polarization corresponding to 0.14–0.4 Ω cm2 at 750°C was achieved in this manner.

A Comparative Study of Variously Prepared Carbon-Supported Pt / MoOx Anode Catalysts for a Polymer Electrolyte Fuel Cell

Carbon-supported anode catalysts were prepared by the preimpregnation, postimpregnation, and chemical reduction methods. The physicochemical characteristics of all catalysts were determined by X-ray diffraction, scanning transmission electron microscopy, and CO pulse titration. The electrochemical oxidation of CO verified from CO-stripping voltammetry shows that most of the were oxidized on the Pt sites. The catalyst prepared by the chemical reduction method showed superior hydrogen electrochemical oxidation in pure , apparently due to the much smaller Pt particle size than those of the other catalysts. However, the anode performances in the presence of 500 ppm mixture showed that a catalyst with high CO tolerance was derived from the catalyst prepared by postimpregnation method. The oxidation of CO by the water–gas shift (WGS) reaction is shown by the formation of even under an open-circuit condition. With an increase in current, active sites for the WGS reaction is regenerated by electrochemical oxidation of hydrogen.

Modelling Study of Surface Reactions, Diffusion, and Spillover at a Ni/YSZ Patterned Anode

This paper presents a modelling study of the electrochemical hydrogen oxidation reaction at nickel/yttria-stabilized zirconia (Ni/YSZ) patterned anodes. An elementary kinetic reaction-diffusion model accounts for coupled heterogeneous chemistry and transport on the Ni and YSZ surfaces. Charge transfer is modeled as a spillover of adsorbates between the Ni and YSZ surfaces at the three-phase boundary (TPB). No a priori assumptions on rate-determining processes are made. Thermodynamic, kinetic, and transport parameters are compiled from various literature sources serving as a base for quantitative simulations. Seven different spillover reaction pathways of the hydrogen oxidation reaction are compared to experimental patterned anode data obtained previously by Bieberle et al. [ J. Electrochem. Soc. , 148 , A646 (2001)] under a range of operating conditions. Only one reaction pathway, based on two hydrogen spillover reactions, is able to describe consistently the complete experimental data set. A sensitivity analysis for this case allows identification of rate-determining processes. Surface concentrations close to the TPB are predicted to differ from the concentration derived from thermodynamical equilibrium by up to 2 orders of magnitude. The simulation results and the validity of the model are critically discussed. Directions for future theoretical and experimental studies for elucidating the mechanistic details of Ni/YSZ anodes are given.

Investigating the CH4 reaction pathway on a novel LSCF anode catalyst in the SOFC

Abstract For the first time, the perovskite lanthanum strontium cobalt ferrite (LSCF) is demonstrated to exhibit catalytic activity for the direct electrochemical oxidation of CH 4 in a solid oxide fuel cell (SOFC) anode environment for more than 72 h with a steady state flow of CH 4 at 900 °C, producing a maximum of 186 W/cm 2 . Results of the transient response studies suggested that the electrochemical oxidation of CH 4 on the anode produced electricity, H 2 O, and CO 2 via (i) CH 4 decomposition, (ii) electrochemical oxidation of hydrogen to H 2 O, and (iii) electrochemical oxidation of carbon to CO 2 . The formation of CO 2 and CO takes place in a parallel pathway: C + 2O 2− → CO 2 ; C + O 2− → CO; where the intrinsic rate constant for the formation of CO 2 is greater than that of CO.

Ce 0.8 M 0.2 O 2 − δ ( M = Mn , Fe , Ni , Cu ) as SOFC Anodes for Electrochemical Oxidation of Hydrogen and Methane

Oxide anodes such as doped ceria offer improved tolerance for nonidealities in anode environment such as redox cycles, sulfur and other poisons, and hydrocarbons. Mixed-valence transition element in ceria provides an additional redox couple besides Ce4+∕Ce3+ in reduced atmosphere, facilitating its electrocatalytic reaction for oxidation of fuels. This paper presents the electrochemical characteristics of Ce0.8M0.2O2−δ(M=Mn,Fe,Ni,Cu) for oxidation of hydrogen and methane. Ce0.8M0.2O2−δ was synthesized, and crystal phase analysis by X-ray diffraction was performed. Single-phase Ce0.8M0.2O2−δ(M=Mn,Fe,Ni) were formed. A second phase, CuO, was found in the powders with the nominal composition of Ce0.8Cu0.2O2−δ. Ce0.8M0.2O2−δ exhibited stability in reducing atmosphere. In comparison, similar microstructural characteristics were found for Ce0.8M0.2O2−δ(M=Mn,Fe,Cu). However, Ce0.8Ni0.2O2−δ exhibits poor microstructure with large cracks. The electrochemical oxidation of wet hydrogen and wet methane was investigated with impedance spectroscopy by using the three-electrode configuration. It was found that Ce0.8M0.2O2−δ(M=Mn,Fe,Ni,Cu) demonstrates relatively low electrochemical activity in both hydrogen and methane. Regarding low n-type conductivity of transition metal cation-containing ceria, it was suggested that an oxide with a high electronic conductivity be added into the Ce0.8M0.2O2−δ matrix for improvement of the electrode performance.

The electrochemical oxidation of hydrogen at activated platinum electrodes in room temperature ionic liquids as solvents

The oxidation of hydrogen was studied at an activated platinum micro-electrode by cyclic voltammetry in the following ionic liquids: [C 2mim][NTf 2], [C 4mim][NTf 2], [N 6,2,2,2][NTf 2], [P 14,6,6,6][NTf 2], [C 4mim][OTf], [C 4mim][BF 4], [C 4mim][PF 6], [C 4mim][NO 3], [C 6mim]Cl and [C 6mim][FAP] (where [ C n mim ] + = 1 -alkyl- 3 -methylimidazolium , [ N 6 , 2 , 2 , 2 ] + = n -hexyltriethylammonium , [ P 14 , 6 , 6 , 6 ] + = tris ( n -hexyltetradecyl ) phosphonium, [ NTf 2 ] - = bis(trifluoromethylsulfonyl)amide , [ OTf ] - = trifluoromethlysulfonate and [ FAP ] - = tris(perfluoroethyl)trifluorophosphate ). Activation of the Pt electrode was necessary to obtain reliable and reproducible voltammetry. After activation of the electrode, the H 2 oxidation waves were nearly electrochemically and chemically reversible in [ C n mim ] [ NTf 2 ] ionic liquids, chemically irreversible in [C 6mim]Cl and [C 4mim][NO 3], and showed intermediate characteristics in OTf −, [ BF 4 ] - , [ PF 6 ] - , [FAP] − and other [ NTf 2 ] - -based ionic liquids. These differences reflect the contrasting interactions of protons with the respective RTIL anions. The oxidation peaks are reported relative to the half-wave potential of the cobaltocenium/cobaltocene redox couple in all ionic liquids studied, giving an indication of the relative proton interactions of each ionic liquid. A preliminary temperature study (ca. 298–333 K) has also been carried out in some of the ionic liquids. Diffusion coefficients and solubilities of hydrogen at 298 K were obtained from potential-step chronoamperometry, and there was no relationship found between the diffusion coefficients and solvent viscosity. RTILs possessing [ NTf 2 ] - and [FAP] − anions showed the highest micro-electrode peak currents for the oxidation in H 2 saturated solutions, with[C 4mim][NTf 2] being the most sensitive. The large number of available RTIL anion/cation pairs allows scope for the possible electrochemical detection of hydrogen gas for use in gas sensor technology.

Electrochemical behavior of ceria with selected metal electrodes

The electrochemical properties of the metal | doped ceria | metal system have been examined by A.C. impedance spectroscopy at a range of temperatures (575–650 °C) and oxygen partial pressures (8×10 − 26 –0.21 atm). Under reducing conditions, the inverse of the interfacial resistances for both Pt and Au electrodes on samarium-doped ceria (SDC) displayed a p O 2 − 1/4 dependence on oxygen partial pressure and an Arrhenius dependence on temperature with an activation energy of ~ 2.7 eV. The similarity in the characteristics of the two types of electrode materials indicates that the electrochemical oxidation of hydrogen occurs predominantly at the ceria | gas interface. Moreover, the behavior, which is similar to that of the electronic conductivity of SDC, is consistent with the hypothesis that electron migration from the reaction site to the metal current collector is the rate-limiting step.

Preparation and electrochemical properties of Co–Si 3N 4 nanocomposites

Cobalt nanoparticles on an amorphous Si 3N 4 matrix were synthesized by direct ball-milling of Co and Si 3N 4 powders for an improvement of their electrochemical performance. The microstructure, morphology and chemical state of the ball-milled Co–Si 3N 4 composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of Co–Si 3N 4 composites was investigated by galvanostatic charge–discharge process and cyclic voltammetry (CV) technique. It is found that metallic Co nanoparticles of 10–20 nm in size are highly dispersed on the amorphous inactive Si 3N 4 matrix after the ball-milling. The composite with a Co/Si molar ratio of 2/1 shows the optimized electrochemical performance, including discharge capacity and cycle stability. The formation of Co nanoparticles with a good reaction activity is responsible for the discharge capacity of the composites. The reversible faradic reaction between Co and β-Co(OH) 2 is dominant for ball-milled Co–Si 3N 4 composite. The surface modification of the hydrogen storage PrMg 12–Ni composites using Co–Si 3N 4 composites can enhance the initial discharge capacity based on the hydrogen electrochemical oxidation and Co redox reaction.

New synthesis of tungsten carbide particles and the synergistic effect with Pt metal as a hydrogen oxidation catalyst for fuel cell applications

Some new tungsten carbides (WCs) were synthesized by the carburizing of tungsten nitrides (W2N) and tungsten sulfides (WS2) as precursors, which were prepared from different starting materials. The carbides were characterized by BET surface area measurements, XRD, SEM and TEM. WCs synthesized by these procedures afforded higher surface areas than those obtained from a conventional direct carburization of WO3. WC containing a small amount of Pt metal was prepared by a wet impregnation method and evaluated as an anode catalyst for the electrochemical hydrogen oxidation reaction. The property of WC which is associated with its synthetic pathway exerted a significant influence on the catalyst performance. The activity of a binary Pt-WC catalyst was greatly improved by choosing a suitable WC and modifying the preparative method. As a result, it turned out that the mass activity of the Pt-WC catalyst system was superior to the current commercial Pt catalyst although only one-tenth the amount of Pt metal was used. It is thought that there is a synergistic effect between Pt and WC in terms of activity, leading to a drastic reduction in the use of Pt metal. A Pt-WC catalyst system may be regarded as one of the candidates for cost-effective catalysts for the future fuel cell devices.

First-Principles Investigations of Electrochemical Oxidation of Hydrogen at Solid Oxide Fuel Cell Operating Conditions

Elementary mechanisms of electrochemical reactions that take place over solid oxide fuel cell electrodes are not well understood. We present a first-principles approach, combining density functional theory calculations and statistical thermodynamics, aimed at studying electrochemical surface reactions. We have utilized this approach to investigate a mechanism for the electrochemical oxidation of hydrogen on various metal surfaces under solid oxide fuel cell operating conditions. Our analysis shows that oxygen adsorption energy is an excellent descriptor for the electrocatalytic activity of different metals. We demonstrate that the electrochemical activity of metals, as a function of the oxygen adsorption energy, can be described with a volcano plot where weak oxygen–metal binding results in a high anode overpotential loss while highly exothermic interactions of oxygen and a metal surface result in the oxygen-induced poisoning of the electrocatalyst. The observed volcano plots are consistent with experimental observations.