Hydrogen Electrode Reaction Research Articles

The evaluation of the polarization resistance in a tubular electrode and its application to the hydrogen electrode reaction

An alternative method for the determination of the kinetic parameters involved in the elementary steps of the reaction mechanism of the hydrogen electrode reaction is proposed. It is based on the determination of the variation of the polarization resistance in a tubular platinum electrode with a laminar flow of electrolyte as a function of the activity of protons of the electrolyte solution. A theoretical expression that relates the experimental variables and the equilibrium polarization resistance is developed, which takes into account the current distribution along the electrode surface. The results are compared with others obtained previously, contributing to the verification of the kinetic mechanism through a completely different experimental procedure.

The Influence of Mixed Ionic Electronic Conductivity in the Hydrogen Electrode Reaction in Solid State Electrochemical Cells

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Figure of merit for the quality of ZrO 2 coatings on stainless steel and nickel-based alloy surfaces

A figure of merit (FOM) has been developed to define the quality of ceramic (e.g., ZrO 2) coatings on metal and alloy [Type 304SS and Alloy 600] surfaces. Zirconia (ZrO 2) coatings were developed as a means of protecting the metal/alloy surfaces from stress corrosion cracking (SCC) in boiling water reactor (BWR) primary heat transport circuits, by inhibiting the cathodic reaction (reduction of oxygen and hydrogen peroxide) on the surface external to the crack. The distribution of pores in the coating plays an important role in corrosion prevention, such that the lower the porosity of the coating, the better the protection afforded to the system against SCC. Since the reactors operate at high temperature (e.g., at 288 °C under full power conditions), the temperature dependence of the FOM was investigated. The figure of merit (FOM) was developed by measuring impedance data over a wide range of frequency (10 mHz–5 kHz) at temperatures of 25, 100, 200, and 288 °C in hydrogenated, buffered solutions, with the hydrogen electrode reaction (HER) being used as a “fast” redox couple. An “equivalent circuit” analog was first developed from the bare surface impedance data and this analog was then employed in a second step to model the pore bottom in defining the pore distribution on the coated surface. A lognormal distribution (LND) of the pores was assumed and the parameters of the LND were determined using a constrained optimization technique to fit the model to the experimental data for the coated surface at different temperatures. The results suggest that, as temperature increases, the coating becomes more porous, making the substrate more susceptible to corrosion cracking. At 288 °C, 87% of the SS and 85% of the Ni-alloy surfaces become porous with the pore radius varying from 0.0001 cm to 0.01 cm.

Kinetics and Mechanism of the Hydrogen Electrode Reaction on Platinum at Elevated Temperatures

not Available.

Composite Hypo-Hyper-d-Intermetallic and Interionic Phases as Supported Interactive Electrocatalysts

Interactive, strong interbonding and highly electron conductive nonstoichiometric titanium suboxide catalytic supports, Magneli phases (Ti(n)O(2n-1), on average Ti(4)O(7)), have been used in the electrocatalysis of hydrogen (HELR) and oxygen (OELR) electrode reactions with remarkable consequences and advanced achievements. The theory of hypo-hyper-d-interelectronic bonding of transition metal ions and atoms has been employed for selective ordered grafting and shown to stay in the core of the strong metal-support interaction (SMSI) in heterogeneous catalysis and electrocatalysis, and thereby the substantial cause for the improved synergistic activity of composite (electro)catalysts. The same fundament has been the thermodynamic basis for the thermal production of symmetric intermetallic Laves type phases of nanostructured electrocatalysts, in particular the ones with higher oxophilic properties of hypo-d-elements. Remarkably advanced in electrocatalytic activity, highly monatomically dispersed deposits of Pt upon Magneli phases are shown to be unique and highly promising electrocatalysts for the cathodic oxygen reduction (ORR). Nanostructured Au upon a thin nanocrystalline film of anatase titania has been confirmed by X-ray photoelectron spectroscopy (XPS) as a typical classical paradigm of the SMSI, and at the same time affording the basis for gold with strained d-orbitals, as the reversible hydrogen electrode. Magneli phases have been shown to be the best electrocatalytic supports with unique properties both for low temperature PEM fuel cells (LT PEM FCs) with pronounced CO tolerance and water electrolysis in membrane type hydrogen generators.

Structural effects on kinetic properties for hydrogen electrode reactions and CO tolerance along Mo–Pt phase diagram

The effect of structural and surface versus bulk properties of Mo–Pt alloys and intermetallic phases taken along their phase diagram upon kinetic and electrocatalytic features for the cathodic hydrogen evolution (HER) has been investigated and displayed. All specimens along Mo–Pt phase diagram in broader reversible potential range feature Volmer–Tafel mechanism with the catalytic recombination of Tafel as the rate determining step (RDS), while further polarization plot in semi-logarithmic η versus log j system shows Volmer–Heyrowski mechanism with the electrochemical desorption of Heyrowski reaction being the RDS; the extension of the former depends on the degree of MoO 3 coverage and blocking active centers of electrode surface. XPS, UPS, XRD and work function characterization of all specimens revealed congenial volcano plots relative to the same dependence in electrocatalytic activity. As the main observation and rule, the most stable and prevailing Pt content specimens feature the best electrocatalytic and kinetic properties. Activated (MoO 3 free) MoPt 3 and MoPt 4 catalysts feature all along the Tafel plot reversible Tafel catalytic reaction as the RDS, and create properties of super-activity within a broader current density range. It has been pointed out that an intermetallic phase with prevailing Mo atomic percentage (Mo 3Pt 2) features pronounced electrocatalytic properties for the HER. XPS measurements of nanostructured intermetallic phases of the same nominal composition, revealed that oxide species of Mo form solid solution with Pt, while significant portion of Pt surface atoms become screened by two-dimensional Mo oxide clusters. Such a structural modification alters the chemisorptive properties of Pt, so that XPS measurements reveal its partial oxidation, the oxide state being the primary oxide (Pt–OH), that spillovers along with MoO 2OH, both being imposed by adsorptive dissociation of water upon titania (TiO 2). It has been inferred that such structural and surface state a priori defines the overall behavior of composite Mo–Pt electrocatalysts. BRIEFS: Brewer hypo-hyper-d-interelectronic (average) configurational, Interionic and crystal structural effects of composite Laves type intermetallic phases and alloys taken along Mo–Pt phase diagram on kinetic, Synergistic electrocatalytic and super-active properties for hydrogen electrode reactions (HELR) and CO tolerance in macro-size and nanostructured electrodes.

The structural and electrochemical properties of La2Mg(Ni0.8−xCo0.2Alx)9 (x=0–0.03) hydrogen storage electrode alloys

Abstract The effect of Al substitution for Ni on the structure and electrochemical properties of La 2 Mg(Ni 0.8− x Co 0.2 Al x ) 9 ( x = 0–0.03) quinary alloys was investigated. All alloys consisted of a main phase with hexagonal PuNi 3 -type structure and a small quantity of the impurity phase (La,Mg) 2 Ni 7 . The increase of Al substitution in the alloys leads to an increase in both the cell volume and the hydride stability but a decrease in unit cell volume expansion rate. The increase of Al content leads to some decrease in both the discharge capacity and the high-rate dischargeability (HRD) but leads to a significant improvement in cycling stability of the alloys. Among the alloys studied, the alloy with x = 0.02 showed a high discharge capacity of 375.9 mAh/g and the best cycling stability ( S 150 = 77.8%) but a poor high-rate dischargeability (HRD 800 = 8.3%). The decrease of HRD of the alloys is ascribed to the decrease of electrocatalytic activity for the hydrogen electrode reaction and the lower diffusion rate of hydrogen in the bulk of the alloys, while the improvement in cycling stability is mainly attributed to the decrease of V H of the hydride phase.

Electrochemical Study of Hydrogen Electrode Reaction Kinetics on LmNi<sub>3.55</sub>Co<sub>0.75</sub>Mn<sub>0.4</sub>Al<sub>0.3</sub> Alloy Electrode

The exchange current density and the peak current density of the hydrogen electrode reaction on LmNi3.55Co0.75Mn0.4Al0.3 alloy electrode in an aqueous 1M KOH solution, at low hydrogen contents (<0.1 H/M) and elevated temperatures (42-60°C), were studied using potentiostatic polarization techniques. Both measured quantities increased linearly with the increase in hydrogen content in the alloy. On the basis of the difference between the activation energy of the charge transfer and the hydrogen diffusion, it was concluded that the charge transfer reaction represented the rate-determining step of the hydrogen electrode reaction under applied experimental conditions. The decrease of each of these two activation energies with increasing hydrogen content was evidenced, which indicated the existence of other processes occurring in the electrode bulk accompanying the hydrogen diffusion.

Anodic Hydrogen Electrode Reaction in Aluminum Chloride-1-Ethyl-3-methylimidazolium Chloride Ionic Liquids

Anodic Hydrogen Electrode Reaction in Aluminum Chloride-1-Ethyl-3-methylimidazolium Chloride Ionic Liquids

The effect of Al substitution for Ni on the structure and electrochemical properties of AB 3-type La 2Mg(Ni 1− xAl x) 9 ( [formula omitted]) alloys

The effect of replacing part of Ni by Al in La 2MgNi 9 alloy on the structure and electrochemical properties of the thus formed La 2Mg(Ni 1− x Al x ) 9 ( x = 0 – 0.05 ) quaternary alloys was investigated. All alloys consisted of a main phase with hexagonal PuNi 3-type structure and a small quantity of an impurity phase (La 2Ni 7). The increase of Al content in the alloys leads to an increase in both the cell volume and the hydride stability, and leads to a noticeable decrease in cell volume expansion rate ( Δ V / V ) on hydriding. The increase of Al content leads to some decrease in both the discharge capacity and the high-rate dischargeability (HRD) but leads to a significant improvement in cycling stability of the alloys. The decrease of HRD of the alloys is ascribed to the decrease of electrocatalytic activity for the hydrogen electrode reaction and the lower diffusion rate of hydrogen in the bulk of the alloys, while the improvement in cycling stability is mainly attributed to the decrease of V H of the hydride phase.

Electrochemical Impedance Spectroscopy Study of a Hydrogen Electrode Reaction at a Zn Electrode in a Molten LiCl−KCl−LiH System

The hydrogen electrode reaction involving hydride ion, H-, at a Zn electrode is investigated in a molten LiCl-KCl-LiH system at 673 K. The charge-transfer resistances were measured by electrochemical impedance spectroscopy in the overpotential region of 0.10 < or = eta < or = 0.35 V and over the H- concentrations of 1.5 x 10(-4) < or = C(H)- < or = 1.2 x 10(-3) mol cm(-3). The logarithm plot of the charge-transfer resistance against the overpotential at C(H)- = 3.0 x 10(-4) mol cm(-3) gives the symmetry factor, beta, of 0.50 and the exchange current density, j0, of 5.8 x 10(-3)A cm(-2), respectively. Analysis of the dependence of j0 on H- concentration independently gives a beta of 0.55. The reasonable beta values indicate that the H- <==> H(ad)(M) + e- step is rate-determining.

Structural effects on kinetic properties for hydrogen electrode reactions and CO tolerance along Mo-Pt phase diagram

The effect of structural and surface versus bulk properties of Mo-Pt alloys and intermetallic phases taken along their phase diagram upon kinetic and electrocatalytic features for the cathodic hydrogen evolution (HER) has been thoroughly investigated and displayed. All specimens along Mo-Pt phase diagram in broader reversible potential range feature Volmer-Tafel mechanism with the catalytic recombination of Tafel as the rate-determining step (RDS), while further polarization plot in semi logarithmic (vs. log) system shows Volmer-Heyrowski mechanism with the electrochemical desorption of Heyrowski reaction being the RDS; the extension of the former depends on the degree of MoO3 coverage and blocking active centers of electrode surface. XPS, UPS, XRD and work function characterization of all specimens revealed congenial volcano plots relative to the same dependence in electrocatalysis. As the main observation the most stable and prevailing Pt content specimens feature the best electrocatalytic and kinetic properties. Activated (MoO3 free) MoPt3 and MoPt4 catalysts feature all along the Tafel plot reversible Tafel catalytic reaction as the RDS, and create properties of super-activity within a broader current density range. It has been pointed out that an intermetallic phase with prevailing Mo atomic percentage (MoPt3) features pronounced electrocatalytic properties for the HER.

Extended Brewer hypo–hyper- [formula omitted]-interionic bonding theory — I. Theoretical considerations and examples for its experimental confirmation

The Extended Brewer Interactive Interionic Bonding Theory (EBIIBT) has been developed to show the equivalence of interatomic and interionic bonding feature, as well as its effect upon electrocatalytic properties for the hydrogen electrode reactions. The equivalence of interionic hypo–hyper- d-interelectronic interaction in both metallic and any other ionic or their composite states has been proved and inferred. In such a context, the EBIIBT stays in the core of the Strong Metal-Support Interaction (SMSI) effect in heterogeneous catalysis, and the latter is an implied consequence of the former. Thermal Gravimetry (TG) analysis of Temperature Programmed Reduction (TPR) of mixed hypo–hyper- d-electronic oxides of transition elements was broadly employed to prove the extended Brewer theory along the phase diagrams of such constituents, as reflected in dramatically decreased temperatures of their mutual reduction versus the individual metallic ingredients entering into the resulting intermetallic phases or alloys. The same interionic Brewer (and/or intermetallic) bonding effect has also been confirmed both by Underpotential Deposition of hyper- d- upon hypo- d-electronic substrates and vice versa, and by the shift of the bonding peaks in XPS analysis. The former affords the basis for new trends in submonolayer hypo–hyper- d-interelectronic electrocatalysis of transition metals. Thus, it has been pointed out that the term SMSI has primarily a broader hypo–hyper- d-interelectronic interactive sense in both the bonding effectiveness and synergism in electrocatalysis, including bifunctional catalytic meaning as based upon the interionic interactive promotion.

Hydrogen diffusion effects on the kinetics of the hydrogen electrode reaction. Part I. Theoretical aspects

The effect of the hydrogen diffusion on the hydrogen electrode reaction has been studied and rigorous kinetic expressions for the Tafel–Heyrovsky–Volmer mechanism has been derived. The analysis of the dependences of the current density (j) on overpotential (η), particularly oriented to the hydrogen oxidation reaction (hor), leads to the following main results: (i) in the Tafel–Volmer (TV) route, the current density reaches a maximum value (jmax) less or equal to the limiting diffusion current density (jL); (ii) jmax is always equal to jL for the Heyrovsky–Volmer (HV) route; (iii) in the simultaneous occurrence of both routes (THV), the current density always reaches the jL value, although in the range of overpotentials of applied interest (0 ≤ η/V ≤ 0.6) the jmax value, characteristic of the TV route, can also be obtained.

Hydrogen diffusion effects on the kinetics of the hydrogen electrode reaction

The present work proposes a methodology for the evaluation of the kinetic parameters of the hydrogen electrode reaction for the Tafel–Heyrovsky–Volmer mechanism from experimental results corresponding to the study of the hydrogen oxidation on a rotating disc electrode. It is based on the correlation of the experimental dependence j(η,ω) with a theoretical expression together with some constraints that involve the use of the equilibrium polarisation resistance, which reduces the number of adjustable parameters. This methodology was applied to the hydrogen oxidation reaction on a platinum electrode, which was studied in the range 900 ≤ ω/rpm ≤ 8100 and −0.05 ≤ η/V ≤ 0.40 in 0.5 M H2SO4. The results obtained have been discussed in the light of the theoretical treatment described in Part I of this work.

Selective Interactive Grafting of Composite Bifunctional Electrocatalysts for Simultaneous Anodic Hydrogen and CO Oxidation: I. Concepts and Embodiment of Novel-Type Composite Catalysts

The equivalence of interionic hypo-hyper-d-interelectronic interaction (HHDII) in both metallic and any other ionic state and its effect upon electrocatalytic properties for hydrogen electrode reactions has been proved and inferred. Thermal gravimetry (TG) analysis of temperature programmed reduction (TPR) of mixed hypo-hyper-d-electronic oxides of transition elements was broadly employed to prove the interionic bonding effect (the extended Brewer theory) as reflected in dramatically decreased individual temperatures of their mutual reduction into intermetallic phases or alloys. The same interionic (and/or intermetallic) bonding effect has been confirmed both by under potential deposition of hyper-d- upon hypo-d-electronic substrates and vice versa, and by the shift of bonding peaks in X-ray photoelectron spectroscopy analysis. The former affords the basis for new trends in submonolayer hypo-hyper-d-interelectronic electrocatalysis of transition metals. Strong metal support interaction (SMSI) of both individual and composite, prevailingly hyper-d-electronic metallic electrocatalysts upon individual and/or composite, usually hypo-d-electronic oxide substrates have been employed to create and graft (anchor) bifunctional electrocatalysts for simultaneous anodic hydrogen and CO oxidation in low temperature polymer exchange membrane fuel cells. The selective interionic bonding method upon predestined active centers of hypo-d-electronic oxide supports has been adapted to avoid nanostructured colloidal precursors and directly graft (anchor) a priori defined nanosized intermetallic phases and synergetic bifunctional electrocatalysts from decomposition of corresponding stoichiometric mixtures of various individual or intermetallic acetylacetonates. An adapted TG method based on TPR has been properly used to define, control and/or stimulate the homogeneity of the intermetallic crystal bonding and growth of nanostructured composite catalysts, mostly of rather extra strong bonding Brewer intermetallic phases upon proper SMSI oxide supports. Thus, it has been pointed out that the term SMSI has a broader HHDII sense in both the bonding effectiveness and bifunctional catalytic meaning, and in fact stays in the core of such extended Brewer interionic bonding theory. © 2003 The Electrochemical Society. All rights reserved.

Effects of electrochemical reaction and self-stress on hydrogen diffusion in tubular membranes during galvanostatic charging

Based on theories of hydrogen electrode reactions at the palladium surface and self-stresses of hydrogen in thin tubular shells established earlier, we numerically calculate transport properties of hydrogen across a tubular membrane under galvanostatic charging conditions. It is found that the exited hydrogen flux is much less than the charging current since the hydrogen combination reaction takes place at the outer surface. On the other hand, the overall system is in an unstable state after a long time charging; this makes the determination of hydrogen diffusivity difficult in experiments. The theoretical results are in good agreement with experimental data obtained before.

Horiuti’s generalized rate expression and hydrogen electrode reaction

Abstract Horiuti’s generalized rate expression is derived by using a simple model of gas effusion and then developed for heterogeneous catalysis. Characteristics of his expression are pointed out. The expression is used for estimating a rate of hydrogen evolution theoretically by taking mutual repulsive interactions among reacting species into account statistical mechanically to overcome the difficulty Tafel faced with catalytic mechanism. Results calculated on Ni(1 1 1) plane satisfactorily reproduced the experimental data observed on Ni polycrystalline electrode. The last part reviews recent knowledge of the hydrogen evolution reaction at Pt low index planes from which we learn a new information entirely unexpected from a classical idea assuming a single kind of adsorbed hydrogen atom on the surface.

Novel trends in electrocatalysis: Extended Brewer hypo-hyper-d-interionic bonding theory and selective interactive grafting of composite bifunctional electrocatalysts for simultaneous anodic hydrogen

Novel Trends in Electrocatalysis: Extended Brewer Hypo-Hyper-d-lnterionic Bonding Theory and Selective Interactive Grafting of Composite Bifunctional Electrocatalysts for Simultaneous Anodic Hydrogen and CO OxidationThe Extended Brewer Interactive Interionic Bonding Theory (EBIIBT) has been developed to show the equivalence of interatomic and interionic bonding features, and for their mutual combinations, as well as its effect upon electrocatalytic properties for the hydrogen electrode reactions (HELR). The equivalence of interionic hypo-hyper-d-interelectronic interaction in both metallic and any other ionic state and its effect upon electrocatalytic properties for hydrogen electrode reactions (HELR) has been proved and inferred. TG (Thermal Gravimetry) analysis of TPR (Temperature Programmed Reduction) of mixed hypc-hyper-d-electronic oxides of transition elements was broadly employed to prove the EBIIBT effect as reflected in dramatically decreased individual temperatures of their mutual reduction into intermetallic phases. The same interionic Brewer (and/or intermetallic) bonding effect has been confirmed both by UPD of hyper-d-upon hypo-d-electronic substrates and vice versa, and by the shift of bonding peaks in XPS analysis.

Evaluation of the kinetic parameters of the hydrogen electrode reaction from the analysis of the equilibrium polarisation resistance

The theoretical expression of the equilibrium polarisation resistance as a function of the partial hydrogen pressure and the activity of protons has been established for the hydrogen electrode reaction operating through the Volmer–Heyrovsky–Tafel mechanism. The corresponding elementary kinetic parameters have been evaluated using experimental results reported in the literature, obtained on smooth platinum electrodes. The advantage of the proposed method for the calculation of these parameters with respect to the conventional determination of the polarisation curves at high overpotential values has been also demonstrated.