Hydrogen Oxidation Activity Research Articles

Properties and development of Ni/YSZ as an anode material in solid oxide fuel cell: A review

Abstract In recent times, synthesis, development and fabrication of anode component of solid oxide fuel cell (SOFC) have gained a significant importance, especially after the advent of anode supported SOFC. The function of the anode electrode involves the facilitation of fuel gas diffusion, oxidation of the fuel, transport of electrons and transport of by-product of the electrochemical reaction. Although impressive progress has been made in the development of alternative anode materials with mixed conducting properties and few of the other composite cermets, Ni/YSZ continues to be the most sought after anode for high temperature SOFC applications. Despite of its poor carburization and sulfidation capabilities during the operation of SOFC directly on hydrocarbons, Ni/YSZ continues to be the most opted anode electrode material due to its high catalytic activity for hydrogen oxidation, methane reforming, high electronic and ionic conductivity and stability. Present review focuses on the various aspects pertaining to Ni/YSZ as an anode in SOFC. Various factors that influence the ohmic, activation and the concentration polarization contribution of anode while using Ni/YSZ are discussed. Importance of optimizing the composition, microstructure and porosity to minimize the above mentioned polarizations are discussed extensively. Various synthesis methods that are used in the preparation of optimized NiO/YSZ composite powder and the methods that are adopted to fabricate anode component are provided in detail in the article. Information on Ni/YSZ anode failure and strategies to improve the long term stability are also discussed exhaustively. Parameters that influence the carburization and sulfidation of Ni/YSZ while using hydrocarbons as fuel are elaborated in this article and means to minimize the same are also discussed.

Investigation of the active sites of rhodium sulfide for hydrogen evolution/oxidation using carbon monoxide as a probe.

Carbon monoxide (CO) was observed to decrease the activity for hydrogen evolution, hydrogen oxidation, and H2-D2 exchange on rhodium sulfide, platinum, and rhodium metal. The temperature at which the CO was desorbed from the catalyst surface (detected by recovery in the H2-D2 exchange activity of the catalyst) was used as a descriptor for the CO binding energy to the active site. The differences in the CO desorption temperature between the different catalysts showed that the rhodium sulfide active site is not metallic rhodium. Using density functional theory, the binding energy of CO to the Rh sites in rhodium sulfide is found comparable to the binding energy on Pt. Coupled with experiment this supports the proposition that rhodium rather than sulfur atoms in the rhodium sulfide are the active site for the hydrogen reaction. This would indicate the active sites for hydrogen evolution/oxidation as well as oxygen reduction (determined by other groups using X-ray absorption spectroscopy) may be the same.

Carbon nanocages: A new support material for Pt catalyst with remarkably high durability

Low durability is the major challenge hindering the large-scale implementation of proton exchange membrane fuel cell (PEMFC) technology, and corrosion of carbon support materials of current catalysts is the main cause. Here, we describe the finding of remarkably high durability with the use of a novel support material. This material is based on hollow carbon nanocages developed with a high degree of graphitization and concurrent nitrogen doping for oxidation resistance enhancement, uniform deposition of fine Pt particles, and strong Pt-support interaction. Accelerated degradation testing shows that such designed catalyst possesses a superior electrochemical activity and long-term stability for both hydrogen oxidation and oxygen reduction relative to industry benchmarks of current catalysts. Further testing under conditions of practical fuel cell operation reveals almost no degradation over long-term cycling. Such a catalyst of high activity, particularly, high durability, opens the door for the next-generation PEMFC for “real world” application.

How the structure of the large subunit controls function in an oxygen-tolerant [NiFe]-hydrogenase

Salmonella enterica is an opportunistic pathogen that produces a [NiFe]-hydrogenase under aerobic conditions. In the present study, genetic engineering approaches were used to facilitate isolation of this enzyme, termed Hyd-5. The crystal structure was determined to a resolution of 3.2 Å and the hydro-genase was observed to comprise associated large and small subunits. The structure indicated that His229 from the large subunit was close to the proximal [4Fe–3S] cluster in the small subunit. In addition, His229 was observed to lie close to a buried glutamic acid (Glu73), which is conserved in oxygen-tolerant hydrogenases. His229 and Glu73 of the Hyd-5 large subunit were found to be important in both hydrogen oxidation activity and the oxygen-tolerance mechanism. Substitution of His229 or Glu73 with alanine led to a loss in the ability of Hyd-5 to oxidize hydrogen in air. Furthermore, the H229A variant was found to have lost the overpotential requirement for activity that is always observed with oxygen-tolerant [NiFe]-hydrogenases. It is possible that His229 has a role in stabilizing the super-oxidized form of the proximal cluster in the presence of oxygen, and it is proposed that Glu73could play a supporting role in fine-tuning the chemistry of His229 to enable this function.

Conducting carbon/polymer composites as a catalyst support for proton exchange membrane fuel cells

SUMMARY Carbon/poly(3,4-ethylene dioxythiophene) (C/PEDOT) composites are synthesized by in situ chemical oxidative polymerization of EDOT monomer on carbon black in order to decrease carbon corrosion that occurred in carbon-supported catalysts used in proton exchange membrane fuel cell. The effects of different dopants including polystyrene sulfonic acid, p-toluenesulfonic acid and camphorsulfonic acid with the addition of ethylene glycol or dimethyl sulfoxide on the properties of the composites are investigated. The synthesized composites are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, surface area analysis and scanning electron microscope. Electrical conductivity is determined by using the four-point probe technique. Electrochemical oxidation characteristics of the synthesized C/PEDOT composites are investigated by cyclic voltammetry by applying 1.2 V for 24 h. The composite prepared at 25 °C with p-toluenesulfonic acid and ethylene glycol shows the best carbon corrosion resistance. Platinum-supported catalyst by using this composite was prepared using microwave irradiation technique, and it was seen that the prepared catalyst did not significantly lose its hydrogen oxidation and oxygen reduction reaction activities after electrochemical oxidation. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of heat treatment on the activity and stability of carbon supported PtMo alloy electrocatalysts for hydrogen oxidation in proton exchange membrane fuel cells

The effect of heat treatment on the activity, stability and CO tolerance of PtMo/C catalysts was studied, due to their applicability in the anode of proton exchange membrane fuel cells (PEMFCs). To this purpose, a carbon supported PtMo (60:40) alloy electrocatalyst was synthesized by the formic acid reduction method, and samples of this catalyst were heat-treated at various temperatures ranging between 400 and 700 °C. The samples were characterized by temperature programmed reduction (TPR), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), cyclic voltammetry (CV), scanning electron microscopy (SEM) and wavelength dispersive X-ray spectroscopy (WDS). Cyclic voltammetry was used to study the stability, and polarization curves were used to investigate the performance of all materials as CO tolerant anode on a PEM single cell text fixture. The catalyst treated at 600 °C, for which the average crystallite size was 16.7 nm, showed the highest hydrogen oxidation activity in the presence of CO, giving an overpotential induced by CO contamination of 100 mV at 1 Acm−2. This catalyst also showed a better stability up to 5000 potential cycles of cyclic voltammetry, as compared to the untreated catalyst. CV, SEM and WDS results indicated that a partial dissolution of Mo and its migration/diffusion from the anode to the cathode occurs during the single cell cycling. Polarization results showed that the catalytic activity and the stability can be improved by a heat treatment, in spite of a growth of the catalyst particles.

Mathematical models for water vapor absorption on catalyst and adsorbent in atmosphere detritiation and correlation of oxidation rate of hydrogen

Establishment of tritium recovery system is necessary to prevent its leakage to the working area. The catalytic oxidation and adsorption process is the most valid method to recover tritium into the working area of those facilities. Therefore, there is a necessity that the tritium recovery system with large-scale and higher integrity is developed and constructed. For this purpose, it is required to obtain and accumulate updated database for chemical engineering design based on most recently commercial and available catalysts and adsorbents. In this work, we selected an adsorbent and catalysts, and examined their adsorption characteristics for water vapor. Adsorption isotherms were studied with a volumetric gas adsorption instrument. Various adsorption models were tested to correlate the experimental isotherms. For the catalyst, catalytic activity for oxidation of hydrogen was investigated in wet gas conditions. The experimental isotherms were successfully correlated using multi-site Langmuir–Freundlich equations. The catalytic activity was found to be influenced by the amount of water vapor adsorbed on the catalyst substrate.

Nickel catalysts for hydrogen evolution from CsH2PO4

Unsupported nickel was evaluated as an electrocatalyst material in an electrochemical hydrogen pump using the superprotonic solid acid CsH2PO4 as a proton exchange membrane. In humidified hydrogen at 250 °C, Ni-based electrodes display a stable proton reduction current of 207 mA cm−2 at a −0.2 V cell potential. Electrodes utilizing carbon-supported Pt catalysts evolved hydrogen at 558 mA cm−2 under identical conditions. Hydrogen evolution and oxidation are reversible on Pt, but hydrogen oxidation activity is virtually absent on Ni.

Enhanced hydrogen oxidation activity and H2S tolerance of Ni-infiltrated ceria solid oxide fuel cell anodes

The effect of Ni infiltration into porous Gd-doped ceria (GDC) anodes on their H2 oxidation performance, with and without added 10 ppm H2S, is reported here. Porous GDC anodes (ca. 10 μm thick) were deposited on yttria stabilized zirconia (YSZ) supports and then infiltrated with catalytic amounts of a Ni nitrate solution, followed by electrochemical testing in a 3-electrode half-cell setup at 500–800 °C. Infiltration of 3 wt.% Ni into the porous GDC anode lowered the polarization resistance by up to 85%, affecting mainly the low frequency impedance arc. When exposed to 10 ppm H2S, the Ni-infiltrated anodes exhibited a ca. 5 times higher tolerance toward sulfur poisoning compared to GDC anodes alone, also showing excellent long-term stability in 10 ppm H2S. In the presence of H2S, it is proposed that Ni, likely distributed as a nanophase, helps to maintain a clean GDC surface at the Ni/GDC interface at which the H2 oxidation reaction takes place. In turn, the GDC will readily supply oxygen anions to the adjacent Ni surfaces, thus helping to remove adsorbed sulfur.

Gas-Phase Chemistry to Understand Electrochemical Hydrogen Evolution and Oxidation on Doped Transition Metal Sulfides

RuS2 and cobalt-doped RuS2 are good catalysts for electrochemical hydrogen evolution in a hydrogen bromine proton exchange membrane based electrochemical flow cell, but their activity for hydrogen oxidation is low. We used temperature programmed reaction (TPR) methods to study the formation of HD from gaseous H2 and D2 catalyzed by these electrode materials. We found that they are active for HD exchange at room temperature and conclude that electrochemical hydrogen oxidation is not limited by the inability of the electrodes to adsorb or dissociate hydrogen. Therefore, we further conclude that the low activity for hydrogen electrooxidation on these semiconducting chalcogenides is due to electronic factors which limit the ability of the semiconductors to accept electrons or pass current. We recommend therefore the use of conducting compounds stable in HBr.

Bismuth effect on the Co–Mn/Ce0.85Zr0.15O2 nanoparticulate for CO preferential oxidation in simulated syngas

The novel and efficient bismuth modified supported Co–Mn catalysts were prepared and employed to catalyze the preferential oxidation of CO (CO PROX) in simulated syngas. The effects of introducing-methods and loadings of bismuth on both catalytic performance and catalyst nature were investigated. The N2 adsorption/desorption measurement, X-ray diffraction (XRD) and H2-temperature programmed reduction (H2-TPR), and O2-TPD (O2-temperature programmed desorption) characterization techniques were performed to reveal the relationship between the catalytic properties and the nature of the catalysts. Results demonstrate that the as-prepared Bi modified supported Co–Mn catalyst exhibits excellent catalytic performance, depending on the introducing method and loadings of Bi. The enhancement of Bi addition into supported Co–Mn catalyst in the catalytic performance for CO PROX reaction is mainly ascribed to the dramatically improved reducibility of the Bi modified sample. Moreover, the decrease in hydrogen transformation over the Bi modified samples can be observed, suggesting the introduction of Bi can compress the catalytic activity for hydrogen oxidation. This study definitely demonstrates the existence of synergistic effect between the added bismuth and Co–Mn/Ce0.85Zr0.15O2 in the Bi modified supported Co–Mn catalyst for CO PROX reaction. The developed Co3O4–MnOx/Ce0.85Zr0.15O2–Bi2O3 catalyst with bismuth content of 4.2 wt.% presents the outstanding catalytic activity, selectivity, and durability for CO PROX reaction in the simulated syngas, and it can be considered as a promising candidate for highly efficient CO elimination from H2-rich stream.

Contribution of Hydrogenase 2 to Stationary Phase H2 Production by Escherichia coli During Fermentation of Glycerol

Escherichia coli has four hydrogenases (Hyd), three genes of which are encoded by the hya, hyb, and hyc operons. The proton-reducing and hydrogen-oxidizing activities of Hyd-2 (hyb) were analyzed in whole cells grown to stationary phase and cell extracts, respectively, during glycerol fermentation using novel double mutants. H2 production rate at pH 7.5 was decreased by ~3.5- and ~7-fold in hya and hyc (HDK 103) or hyb and hyc (HDK 203) operon double mutants, respectively, compared with the wild type. At pH 6.5, H2 production decreased by ~2- and ~5-fold in HDK103 and HDK203, respectively, compared with the wild type. At pH 5.5, H2 production was reduced by ~4.5-fold in the mutants compared with the wild type. The total hydrogen-oxidizing activity was shown to depend on the pH of the growth medium in agreement with previous findings and was significantly reduced in the HDK103 or HDK203 mutants. At pH 7.5, Hyd-2 activity was 0.26 U (mg protein)(-1) and Hyd-1 activity was 0.1 U (mg protein)(-1). As the pH of the growth medium decreased to 6.5, Hyd-2 activity was 0.16 U (mg protein)(-1), and Hyd-1 was absent. Surprisingly, at pH 5.5, there was an increase in Hyd-2 activity (0.33 U mg protein)(-1) but not in that of Hyd-1. These findings show a major contribution of Hyd-2 to H2 production during glycerol fermentation that resulted from altered metabolism which surprisingly influenced proton reduction.

Zymographic differentiation of [NiFe]-Hydrogenases 1, 2 and 3 of Escherichia coli K-12

BackgroundWhen grown under anaerobic conditions, Escherichia coli K-12 is able to synthesize three active [NiFe]-hydrogenases (Hyd1-3). Two of these hydrogenases are respiratory enzymes catalysing hydrogen oxidation, whereby Hyd-1 is oxygen-tolerant and Hyd-2 is considered a standard oxygen-sensitive hydrogenase. Hyd-3, together with formate dehydrogenase H (Fdh-H), forms the formate hydrogenlyase (FHL) complex, which is responsible for H2 evolution by intact cells. Hydrogen oxidation activity can be assayed for all three hydrogenases using benzyl viologen (BV; Eo′ = -360 mV) as an artificial electron acceptor; however ascribing activities to specific isoenzymes is not trivial. Previously, an in-gel assay could differentiate Hyd-1 and Hyd-2, while Hyd-3 had long been considered too unstable to be visualized on such native gels. This study identifies conditions allowing differentiation of all three enzymes using simple in-gel zymographic assays.ResultsUsing a modified in-gel assay hydrogen-dependent BV reduction catalyzed by Hyd-3 has been described for the first time. High hydrogen concentrations facilitated visualization of Hyd-3 activity. The activity was membrane-associated and although not essential for visualization of Hyd-3, the activity was maximal in the presence of a functional Fdh-H enzyme. Furthermore, through the use of nitroblue tetrazolium (NBT; Eo′ = -80 mV) it was demonstrated that Hyd-1 reduces this redox dye in a hydrogen-dependent manner, while neither Hyd-2 nor Hyd-3 could couple hydrogen oxidation to NBT reduction. Hydrogen-dependent reduction of NBT was also catalysed by an oxygen-sensitive variant of Hyd-1 that had a supernumerary cysteine residue at position 19 of the small subunit substituted for glycine. This finding suggests that tolerance toward oxygen is not the main determinant that governs electron donation to more redox-positive electron acceptors such as NBT.ConclusionsThe utilization of particular electron acceptors at different hydrogen concentrations and redox potentials correlates with the known physiological functions of the respective hydrogenase. The ability to rapidly distinguish between oxygen-tolerant and standard [NiFe]-hydrogenases provides a facile new screen for the discovery of novel enzymes. A reliable assay for Hyd-3 will reinvigorate studies on the characterisation of the hydrogen-evolving FHL complex.

Hydrogen electrooxidation on PdAu supported nanoparticles: An experimental RDE and kinetic modeling study

The influence of the apparent Pd coverage on Au nanoparticles on the kinetics of the hydrogen oxidation (HOR) reaction has been explored by combined experimental rotating disc and microkinetic modeling study. PdAu bimetallic electrodes with variable Pd coverage in the interval from 0.07 to 2MLs were obtained by electrodeposition of Pd on carbon supported Au nanoparticles. The experimental rotating disc electrode curves have been analyzed with the help of a kinetic model, in order to shed light on the predominant HOR mechanism (Heyrovsky–Volmer vs. Tafel–Volmer), the nature of the rate determining step, and their dependence on the Pd coverage, and get an insight into the type of HOR intermediate. The kinetic modeling suggests that the Heyrovsky–Volmer mechanism can reproduce the experimental curves for the whole range of Pd coverages explored. However, the Tafel step cannot be fully discarded around the equilibrium potential, its eventual contribution increasing as the coverage of Pd is reduced. The results of this work support a weakly adsorbed Had intermediate in the HOR on Pd, its Gibbs energy of adsorption decreasing from positive to near-zero values with the decrease of the apparent Pd coverage, underlying the enhancement of the hydrogen oxidation activity of PdAu compared to pure Pd.

Electrodeposited Pd Sub-Monolayers on Carbon-Supported Au Particles of Few Nanometers in Size: Electrocatalytic Activity for Hydrogen Oxidation and CO Tolerance Vs. Pd Coverage

A series of Pd–Au/C catalysts were obtained by selective electrodeposition of various amounts of Pd metal from a H2PdCl4 solution onto the carbon-supported Au nanoparticles (mainly below 5 nm in diameter) synthesized by “cationic adsorption” technique. The catalytic performance of the Pd–Au particles with both the clean and carbon monoxide (CO)-blocked surfaces for the hydrogen oxidation reaction (HOR) at 25 and 60 °C was tested as a function of the Pd coverage (θPd) expressed in effective monolayer (ML) units, using a rotating disk electrode (RDE). The RDE studies demonstrate superior HOR activity (per unit of Pd surface area) of Pd deposited at the submonolayer level (θPd < 0.65 ML) onto the finely dispersed Au particles in comparison to those observed for the low-dispersed Pd–Au/C catalysts described earlier by other authors and for the monometallic Pd particles. The dependencies of the HOR activity and CO tolerance of the finely dispersed Pd–Au particles on their surface composition are discussed in terms of occurrence of various Pd sites on the surface of bimetallic particles differing in their ability to catalyze HOR and adsorb CO. The relative contribution of various factors to the rise of CO tolerance observed for Pd deposited on Au at varying θPd was estimated by comparison of the HOR activities measured with the fresh and CO-poisoned Pd–Au/C catalysts.

Role of the NiFe Hydrogenase Hya in Oxidative Stress Defense in Geobacter sulfurreducens

Geobacter sulfurreducens, an Fe(III)-reducing deltaproteobacterium found in anoxic subsurface environments, contains 4 NiFe hydrogenases. Hyb, a periplasmically oriented membrane-bound NiFe hydrogenase, is essential for hydrogen-dependent growth. The functions of the three other hydrogenases are unknown. We show here that the other periplasmically oriented membrane-bound NiFe hydrogenase, Hya, is necessary for growth after exposure to oxidative stress when hydrogen or a highly limiting concentration of acetate is the electron source. The beneficial impact of Hya on growth was dependent on the presence of H(2) in the atmosphere. Moreover, the Hya-deficient strain was more sensitive to the presence of superoxide or hydrogen peroxide. Hya was also required to safeguard Hyb hydrogen oxidation activity after exposure to O(2). Overexpression studies demonstrated that Hya was more resistant to oxidative stress than Hyb. Overexpression of Hya also resulted in the creation of a recombinant strain better fitted for exposure to oxidative stress than wild-type G. sulfurreducens. These results demonstrate that one of the physiological roles of the O(2)-resistant Hya is to participate in the oxidative stress defense of G. sulfurreducens.

Reversible Electrocatalytic Production and Oxidation of Hydrogen at Low Overpotentials by a Functional Hydrogenase Mimic

An efficient ligand combination: A new bis(diphosphine) nickel(II) complex (see picture) is described. A ΔG° value of 0.84 kcal mol−1 for hydrogen addition for this complex was calculated from the experimentally determined equilibrium constant. This complex displayed reversible electrocatalytic activity for hydrogen production and oxidation at low overpotentials, which are characteristic for hydrogenase enzymes.

Lanthanum modified nickel-based anode of SOFCs

The effects of adding lanthanum to the nickel-based anode on the cell performances were studied. Because lanthanum can react with nickel and zirconium, it can hinder the sintering of nickel and yttrium stabilized zirconium (YSZ) and improve the interfacial contact between Ni and YSZ on the anode. When 10% (mol) lanthanum was added to the anode, the particles in the anode became smaller and better interfacial contact and the distribution was more uniform than Ni-YSZ anode, which led to a great decrease of the polarization resistance and a great increase of the activity for electrochemical oxidation of hydrogen. When the content of lanthanum added to NiO was 10 mol %, the cell maximum power density increased to 1.61W/cm2 from 1.33 W/cm2 of the Ni-YSZ anode cell at 800 oC. When the lanthanum content increased to 20% (mol), a large amount of La2Zr2O7 was formed, which led to both the decrease of the electronic conductivity of anode and the decrease of the cell performance.

The respiratory molybdo-selenoprotein formate dehydrogenases of Escherichia coli have hydrogen: benzyl viologen oxidoreductase activity

BackgroundEscherichia coli synthesizes three membrane-bound molybdenum- and selenocysteine-containing formate dehydrogenases, as well as up to four membrane-bound [NiFe]-hydrogenases. Two of the formate dehydrogenases (Fdh-N and Fdh-O) and two of the hydrogenases (Hyd-1 and Hyd-2) have their respective catalytic subunits located in the periplasm and these enzymes have been shown previously to oxidize formate and hydrogen, respectively, and thus function in energy metabolism. Mutants unable to synthesize the [NiFe]-hydrogenases retain a H2: benzyl viologen oxidoreductase activity. The aim of this study was to identify the enzyme or enzymes responsible for this activity.ResultsHere we report the identification of a new H2: benzyl viologen oxidoreductase enzyme activity in E. coli that is independent of the [NiFe]-hydrogenases. This enzyme activity was originally identified after non-denaturing polyacrylamide gel electrophoresis and visualization of hydrogen-oxidizing activity by specific staining. Analysis of a crude extract derived from a variety of E. coli mutants unable to synthesize any [NiFe]-hydrogenase-associated enzyme activity revealed that the mutants retained this specific hydrogen-oxidizing activity. Enrichment of this enzyme activity from solubilised membrane fractions of the hydrogenase-negative mutant FTD147 by ion-exchange, hydrophobic interaction and size-exclusion chromatographies followed by mass spectrometric analysis identified the enzymes Fdh-N and Fdh-O. Analysis of defined mutants devoid of selenocysteine biosynthetic capacity or carrying deletions in the genes encoding the catalytic subunits of Fdh-N and Fdh-O demonstrated that both enzymes catalyze hydrogen activation. Fdh-N and Fdh-O can also transfer the electrons derived from oxidation of hydrogen to other redox dyes.ConclusionsThe related respiratory molybdo-selenoproteins Fdh-N and Fdh-O of Escherichia coli have hydrogen-oxidizing activity. These findings demonstrate that the energy-conserving selenium- and molybdenum-dependent formate dehydrogenases Fdh-N and Fdh-O exhibit a degree of promiscuity with respect to the electron donor they use and identify a new class of dihydrogen-oxidizing enzyme.

Characterization of Sr1-xLaxTi1-yCryO3-δ-GDC Composite Anodes for Direct Use of CH4 in SOFC

not Available.