Oxygen Electroreduction Reaction Research Articles

Operating Alkaline Alcohol Fuel Cell (ITAAFC) in Intermediate-Temperature Range

Direct alcohol fuel cells (DAFCs) possess obvious advantages over traditional hydrogen fuel cells in terms of hydrogen storage, transportation, and the utilization of existing infrastructure. However, the commercialization of this fuel cell technology based on the use of proton-conductive polymer membranes has been largely hindered by its low power density owing to the sluggish kinetics of both anode and cathode reactions in acidic media and high cost owing to the use of noble metal catalysts. These could be potentially addressed by the development of alkaline alcohol fuel cells (AAFCs). In alkaline media, the polarization characteristics of alcohol electrooxidation and oxygen electroreduction are far superior to those in acidic media. Another obvious advantage of using alkaline media is less-limitations of electrode materials. The replacement of Pt catalysts with non-Pt catalysts will significantly decrease the cost of catalysts. Recently, the AAFCs have received increased attention. However, these fuel cells are normally operated at temperature lower than 80 °C. In this low temperature range, both methanol electrooxidation and oxygen electroreduction reactions are not sufficiently facile for the development of high performance AAFCs. Considerable undergoing efforts are now focused on the development of highly active catalysts for accelerated electrode reactions.Alternatively, increasing temperature has been proven as an effective way to accelerate electrode reactions. The changes of the reaction rates with increasing temperature are strongly determined by the values of activation energy, as described by the Arrhenius equation. More obvious changes are expected for alcohol electrooxidation in alkaline media than in acidic media since reported values of the activation energy are higher in alkaline media. Additionally, increasing temperature may decrease concentration polarization, Ohmic polarization, and CO poisoning of the catalysts. All these advantages can contribute to the performance improvement of the AAFCs.In an intermediate temperature range of 80 to 200 oC, CO is likely to spontaneously react with OH- to give formate as follows [1]: (1)Because formate produced via Reaction I is soluble and more electrochemically active than CO on Pt, surface CO formed during alcohol oxidation would be readily removed, resulting in considerable decrease in the CO-poisoning of Pt-based catalysts. Moreover, the kinetics of the alcohol oxidation in alkaline media on Pt has been suggested to be largely determined by the reaction between the surface CO and surface oxygen-containing species (OH), following a Langmuir-Hinshinwood mechanism. Accordingly, accelerated electrooxidation of CO intermediate would increase the rate of the alcohol oxidation.Further finding of increasing temperature for the methanol oxidation is that methanol can be efficiently converted with water in the aqueous phase over appropriate heterogeneous catalysts at temperatures near 200 oC to produce primarily H2 and CO2 [2]. (2)During the methanol liquid-phase reforming, trace amount of methane is the side product and the use of more basic catalyst favors H2 production. The methanol reforming indicates that sluggish methanol oxidation reaction which has plagued low temperature DAFCs, could become highly facile in alkaline media at temperatures close to 200 oC where the reforming of methanol is triggered. Substantially accelerated electrooxidation of methanol would make it possible to achieve low anode overpotentials. Therefore, driving the electrooxidation of methanol in an intermediate-temperature range over the methanol-boiling temperature (around 80 oC) and the triggering temperature of the methanol reforming (about 200 oC) would be of academic and practical importance for the development of high performance a technology.We have investigated systematically the electrocatalysis associated with the ITAAFC and demonstrated high performance of this promising fuel cell technology. Our status-of-the-art ITAAFC operating with methanol at 120 oC demonstrated a peak power density of around 250 mW cm-2 at around 700 mA cm-2.

The kinetics of oxygen electroreduction: A long way from iron rust to lithium-air batteries

In this communication, we review the details of the oxygen electroreduction reaction on rust layers, passive iron and well defined iron oxides as cathodes for the reaction. In particular, we highlight the important electrocatalytic role of Fe(II) sites at the surface of the oxides in contact with the aqueous electrolyte. When the same reaction takes place at bifunctional cathodes with separated metal anodes which gives rise to metal–air batteries on which much attention has been paid recently in connection with electric vehicles.

Investigation of a Carbon-Supported Pt Electrode for Oxygen Reduction Reaction in 0.1M KOH Aqueous Solution

The carbon-supported Pt nanoclusters (20 wt% metal) electrodes have been tested as oxygen reduction catalysts in 0.1M KOH solutions. The novel non-conventional microporous-mesoporous carbide derived carbon powder, synthesized from molybdenum carbide (Mo2C) at 750°C using the high-temperature chlorination method, has been used as an electrocatalyst support for oxygen electroreduction. For comparison, the corresponding parameters for commercially available VulcanXC72 and (20 wt%) Pt-VulcanXC72 have been obtained. Results of the X-ray diffraction analysis show that the Pt nanoclusters have been deposited mainly as the face-centered cubic (fcc) crystals at both carbon supports. The Pt particles were distributed uniformly on the porous carbon supports, and the average particle size of the Pt nanoclusters at (20 wt%) Pt-C(Mo2C) and at (20 wt%) Pt-VulcanXC72 were 42 and 57 Å, respectively. The (20 wt%) Pt-C(Mo2C) catalyst demonstrated higher activity (calculated effective electrochemical surface area Aeff = 0.485 cm2) with high specific surface area SBET = 1600 m2 g−1 toward the oxygen electroreduction reaction at room temperature compared with that for the (20 wt%) Pt-VulcanXC72 (Aeff = 0.320 cm2) with SBET = 180 m2 g−1. The four-electron oxygen reduction mechanism has been established for both, i.e., the (20 wt%) Pt-C(Mo2C) and (20 wt%) Pt-VulcanXC72 catalysts based electrodes.

Influence of Molecular Isomerism of Monopyridylporphyrin on Electrochemical and Electrocatalytic Properties in Alkaline Solution

The comparative investigation of the electrochemical reduction of a number of pyridylporphyrin derivatives with alkyl substituents and their cobalt(II) complexes in 0.1 M KOH is carried out by cyclic voltammetry (CV). The influence of isomerism of the porphyrin molecule and the nature of metal on the oxidative capacity of the tetrapyrrole macrocycle and on the electrocatalytic activity of compounds studied for the oxygen electroreduction reaction is established.

Impact of the Pt catalyst on the oxygen electroreduction reaction kinetics on various carbon supports

Micro- and mesoporous carbide-derived carbons synthesized from molybdenum and tungsten carbides were used as porous supports for a platinum catalyst. Synthesized materials were compared with commercial Vulcan XC72R conducting furnace black. The scanning electron microscopy, X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and low-temperature N2 adsorption methods were applied to characterize the structure of catalysts prepared. The kinetics of oxygen electroreduction in 0.5 M H2SO4 solution was studied using cyclic voltammetry and rotating disk electrode methods. The synthesized carbide-derived carbons exhibited high specific surface area and narrow pore size distribution. The platinum catalyst was deposited onto the surface of a carbon support in the form of nanoparticles or agglomerates of nanoparticles. Comparison of carbide-derived carbons and Vulcan XC72R as a support showed that the catalysts prepared using carbide-derived carbons are more active towards oxygen electroreduction. It was shown that the structure of the carbon support has a great influence on the activity of the catalyst towards oxygen electroreduction.

Electroreduction of molecular oxygen on carbon electrode modified by dispersed silver

Silver particles are formed by electrochemical deposition on the carbon electrode surface. It is found that the deposition process occurs according to the progressive nucleation mechanism, which results in formation of silver particles with the size of 95 to 190 nm as dependent on the electrodeposition time. The values of silver particle size and support surface coverage by metal obtained on the basis of microphotographs indicate that cathodic polarization in the presence of dissolved oxygen results in particle size redistribution due to the reaction of silver particle dissolution with further deposition simultaneously with oxygen electroreduction. The reaction of molecular oxygen electroreduction on a carbon electrode with deposited dispersed silver occurs via a mixed two- and four-electron mechanism. The observed limiting reaction current is of diffusion nature.

Electrochemical and electrocatalytic properties of meso-triphenylcorrole and its complexes with Mn(III), Co(III), Cu(III), and Zn(II)

The method of cyclic voltammetry (CV) was used to compare electrochemical and electrocatalytic properties of meso-triphenylcorrole [H3(ms-Ph)3Cor] and also its complexes with Mn(III), Co(III), Cu(III), and Zn(II) in 0.1M KOH. Metal-localized redox transitions are detected in the complexes of Mn (III → IV) and (III → II), Co (III → II), Cu (III → II). It is shown that the manganese complex features most effective catalytic properties in the reaction of molecular oxygen electroreduction.

Gold autodeactivation during oxygen electroreduction studied by electrochemical impedance spectroscopy

The deactivation of a polycrystalline gold electrode is observed during oxygen electroreduction reaction (ORR) in basic medium. At that, the cause of the process is chemical decomposition of the ORR intermediate and blocking of active sites of the electrode surface by hydroxyl radical-like species. The deactivation mechanism is discussed.

Electrocatalytic properties of the nanostructured electrodes and membranes in hydrogen-air fuel cells

The new catalytic electrodes and electrolytes for fuel cells and their synthesis methods have been described. The catalytic properties of the nanostructured membranes and electrodes are investigated both in vitro and in hydrogen-air fuel cell, in situ. The hybrid perfluorinated membranes, with the inorganic nanosize additives, were synthesized. An acceleration of electrode reactions during testing these membranes in fuel cell was observed. This shows the possibility of promotion effect of inorganic additives in the catalytic reaction of oxygen reduction at the electrode. The investigated membranes have enhanced transport properties, especially at low humidity. The nano-structured electrodes based on carbon nanofibers combined with gas diffusion layer have been developed. The high efficiency of carbon nanofibers grown in diffusion layer as catalyst support was shown; the efficiency of the prepared electrodes for oxygen electroreduction reaction is higher than efficiency of electrodes with the commercial catalyst E-TEK 20% Pt/C.

Rare earth metal oxides as BH4−-tolerance cathode electrocatalysts for direct borohydride fuel cells

Rare earth metal oxides (REMO) as cathode electrocatalysts in direct borohydride fuel cell (DBFC) were investigated. The REMO electrocatalysts tested showed favorable activity to the oxygen electro-reduction reaction and strong tolerance to the attack of BH4− in alkaline electrolytes. The simple membraneless DBFCs using REMO as cathode electrocatalyst and using hydrogen storage alloy as anodic electrocatalyst exhibited an open circuit of about 1 V and peak power of above 60 mW/cm2. The DBFC using Sm2O3 as cathode electrocatalyst showed a relatively better performance. The maximal power density of 76.2 mW/cm2 was obtained at the cell voltage of 0.52 V.

Nature of the Selenium Submonolayer Effect on the Oxygen Electroreduction Reaction Activity of Ru(0001)

I present here results of first principles studies of the adsorption energetics of the intermediates of the oxygen electroreduction reaction (ORR) on a Se-modified Ru(0001) surface. The calculations were performed for 1/3 and 2/3 monolayer coverage of Se, as well as for clean Ru(0001) as a reference. The binding energies of O and OH on Ru(0001) are found to decrease significantly with the presence of Se, and this effect increases with the Se coverage. The Se surface modification is found not to change the Ru local density of electronic states noticeably. However, Se atoms accept electronic charge from the surface and thus become negatively charged. As a result, they repeal electrostatically the adsorbed negatively charged O and OH intermediates and in this way reduce their binding energies. This effect provides an alternative way of tuning the reactivity of the catalyst surfaces. Since for the Ru case reduction of the O and OH binding energies makes ORR energetically favorable, Se modification dramatically improves the ORR rate on Ru. Adsorption of O2 and coadsorption of the ORR intermediates and water have also been studied. The effect of coadsorption on the binding energies of O and OH are discussed.

Co-alloying effect of Co and Cr with Pt for oxygen electro-reduction reaction

The effect of co-alloying of Co and Cr was investigated by synthesizing and analyzing Pt3M and PtM (M=Co and/or Cr) catalysts for the oxygen electro-reduction reaction (ORR) activity. In the Pt3M catalysts, we could not observe significant differences among the alloy catalysts before and after annealing, except for the high specific activity of a Pt3Co/C-900 catalyst (Pt3Co/C catalyst annealed at 900°C under H2/Ar (5.2mol% H2) flow for 5min.). The electrochemical properties of the alloy catalysts were much different in the PtM catalysts. After annealing at 900°C, the specific activities of the PtM catalysts increased in the order of PtCo/C-900 (5000 μA cmpt−2)>PtCo0.5Cr0.5/C-900 (2400 μA cmpt−2)>PtCr/C-900 (1080 μA cmpt−2)>Pt/C (334 μA cmpt−2). On the other hand, ORR mass activity exhibited a different order of PtCo0.5Cr0.5/C-900 (132 mA mgpt−1)>PtCr/C-900 (129 mA mgpt−1)>PtCo/C-900 (37 mA mgpt−1). The low mass activity of the PtCo/C-900 catalyst was explained by small electrochemically active surface area (EAS). The intermediate specific ORR activity and EAS values of the PtCo0.5Cr0.5/C catalyst shows that the two opposite characteristics of PtCo (low mass activity and high specific activity) and PtCr (high mass activity and low specific activity) were combined by co-alloying of Co and Cr with Pt. In addition, this result shows that the electrochemical properties of the ternary catalyst can be tuned by controlling the composition to achieve high mass activity.

Preparation and Electrocatalytic Performance of Thin-shell Ni/Pt Core-shell Nanoparticles

The Ni/Pt core-shell nanoparticles with different shell thicknesses were prepared by composite coating of colloid particles and then characterized by HRTEM, EDS, XPS and XRD. Electrochemical properties for the oxygen electro-reduction reaction and methanol electro-oxidation were measured by potentiodynamic and cyclic voltammetry. The experimental results show that Ni/Pt core-shell nanoparticles are spherical and the mean particle size of Ni1-Pt0.067 is about 7 nm with shell thickness of 1 nm. Compared with Pt/C, Ni/Pt core-shell nanoparticels possess higher activity. Ni1-Pt0.067/C has the highest catalytic activity in these prepared catalysts with different thickness, and its peak current density can reach 143.06 mA/mg in 0.5 mol/L H2SO4 solution, 1.4 times of that of Pt/C for O2 electro-reduction reaction. Peak current density of Ni1-Pt0.067/C for methanol electro-oxidation reaches 538.3 mA/mg in 0.5 mol/L H2SO4+1.0 mol/L CH3OH solution, which is 5.2 times of that of Pt/C. Based on 1 mg Pt, the specific mass activity of Ni1-Pt0.067/C is 30-fold higher than that of Pt/C nanoparticles.

Oxygen reduction reaction on polycrystalline gold. Pathways of hydrogen peroxide transformation in the acidic medium

The mechanism of oxygen electroreduction on polycrystalline gold is studied in the acidic medium. Hydrogen peroxide is the main reaction product. However, two potential regions can be singled out in which the oxygen electroreduction reaction proceeds by different pathways. The first region is the potential interval close to the steady-state potential. Here, the oxygen electroreduction virtually completely produces peroxide. The second interval is the potential range of considerable cathodic polarization values. In this case, peroxide can be reduced to water. The low energy of hydrogen peroxide adsorption on gold determines the considerable overpotential of peroxide reduction. It is shown that on the gold electrode surface, the catalytic decomposition of peroxide occurs. The use of the method of electrochemical impedance spectroscopy allows the peculiarities of the oxygen reaction associated with hydrogen peroxide transformations to be revealed. In the acidic medium, the reactions of consecutive reduction of oxygen through the intermediate formation of hydrogen peroxide and the catalytic decomposition of the intermediate product are shown to proceed simultaneously. The ratio of rate constants of electrochemical stages depends on the potential. The chemical decomposition is observed both near the steady-state potential and in the cathodic region where considerable electrochemical reduction of peroxide occurs.

Electrocatalytic Process on Carbon Paste Electrode Modified with a Fe-5-Aphen Metalcomplex

The electrocatalytical behaviour of carbon paste electrode (CPE) modified with poly Fe(III)-5-Aphen were studied for the oxygen electroreduction reaction (ORR) in acid medium. The ORR on CPE modified electrode follows a mechanism via 4 electrons. Electrokinetic parameters obtained in this work are comparable with those reported for other metallic porphyrins and phthalocyanines used as electrocatalyst. The stability of the CPE modified electrode in the reduction of oxygen is maintained at least for 30 days after been prepared. Only after this time there is a slight modification of the electrode surface with an increase of 50 mV in the cathodic overpotencial for RRO.

Specific features of oxygen electroreduction on platinized carbon black-functionalized carbon nanotube composite

The electrochemical behavior of multiwalled carbon nanotubes (MWCNTs) containing functional surface groups has been studied by the methods of cyclic voltammetry and direct-current polarography with stationary and rotating disk electrodes. The surface catalytic activity of supported platinum in the reaction of molecular oxygen electroreduction and the influence of functionalized MWCNTs on this process were determined.

Functional DMFC Cathode Catalysts and Supports Based on Niobium Oxide Phase

Composite electrocatalysts consisting of platinum nanophase supported on carbon black decorated with niobium oxide phase were prepared by a two step precipitation/reduction procedure. The intrinsic catalytic activity of these materials was evaluated for the oxygen electroreduction reaction, measured in the absence and presence of methanol. It was found that the NbxOy-composite materials are more hydrophilic and thus initially have lower intrinsic catalytic activity for oxygen reduction. However, materials containing NbxOy offer better overall platinum mass utilization, achieved through much better dispersion of the platinum nanophase. Such advantageous dispersion is observed even for high metal loadings. Another advantage of these materials is minimal effect of poisoning with the intermediates formed during methanol oxidation that results in the enhanced methanol tolerance in direct methanol fuel cells (DMFC).

Электровосстановление кислорода в кислом электролите на системе наночастицы золота/углеродный носитель

The synthesis of catalysts 20 Au/C with different degree of dispersion. These systems were investigated for activity in the oxygen electroreduction reaction with methods of the cyclic voltammograms and polarization curves. The increase of rate and depth of process (the number of electrons increases from 2 to 3.5) in the transition from compact to gold nanoparticles.

Heteroatom doped carbons prepared by the pyrolysis of bio-derived amino acids as highly active catalysts for oxygen electro-reduction reactions

Heteroatom (nitrogen and sulfur)-doped carbons were synthesized via the pyrolysis of composites composed of iron chloride, cobalt chloride and five different amino acids (alanine, cysteine, glycine, niacine and valine), and their electrocatalytic activity towards oxygen reduction reactions (ORR) compared with each other for fuel cell applications. In all of the prepared catalysts, carbon was doped by nitrogen, and, in particular, a catalyst synthesized from cysteine was dual-doped with nitrogen and sulfur. Among all the catalysts, the dual-doped carbon showed the highest onset potential (0.55 V, vs. Ag/AgCl) and electrochemical activity in acidic media, − 0.2 mA (at 0.2 V, vs. Ag/AgCl), which is about 43% of that of commercial Pt/C (40 wt%). XPS revealed that sulfur was doped in the carbon as sulfate or sulfonate, and it is surmised that not only nitrogen doping but also sulfur doping of carbon plays a key role in improving its electrocatalytic activity towards ORR.

Pd@Pt Core−Shell Nanostructures with Controllable Composition Synthesized by a Microwave Method and Their Enhanced Electrocatalytic Activity toward Oxygen Reduction and Methanol Oxidation

Three-dimensional Pd@Pt core−shell nanostructures with controllable shape and composition were synthesized by using a one-step microwave heating method. The nanostructures with the morphology, structure, and composition being easily controlled through adjusting the molar ratio between Pt and Pd precursor were characterized by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), X-ray powder diffraction (XRD), and energy-dispersive X-ray (EDX) techniques. In addition, the electrocatalytic characteristics of these prepared Pd@Pt electrocatalysts with different Pd/Pt molar ratio for oxygen electro-reduction reaction (ORR) and methanol electro-oxidation reaction (MOR) were systematically investigated by voltammetry. The results show that Pd@Pt electrocatalysts exhibit higher catalytic activity than pure Pd and pure Pt catalysts for both the ORR and MOR, and the highest activity is obtained at the Pd@Pt electrocatalyst with a Pd/Pt molar ratio of 1:3. This result demonstrates that a higher performance of ORR and MOR could be realized at the novel core−shell electrocatalyst while Pt utilization also could be diminished. This method may open a general approach for the shape-controlled synthesis of bimetallic Pt−M nanocatalysts, which can be expected to have promising applications in fuel cells.