CO Oxidation Potential Research Articles

Microfabricated electrochemical gas sensor

The fabrication and working principle of an electrochemical gas sensor for direct gas phase detection of organic molecules is presented. The sensor is composed of two Pt electrodes where redox reactions can occur, and an ion exchange membrane to conduct H+ from an electrode to the other. As proton exchange membrane they used a spin-coated Nafion® layer. An underlying SU-8 layer assures a double role of adhesion of the Nafion to the substrate and water reservoir to limit dehydration of the Nafion. The sensor is characterised for its electrochemical properties and tested for the detection of CO as model pollutant. The detection tests are performed in the form of cyclic voltammetry, and show that the sensor can detect the gas at the applied voltage corresponding to the oxidation potential of CO into CO2.

Efficient CO Oxidation Using Dendrimer-Encapsulated Pt Nanoparticles Activated with

In this paper, we show that the onset potential for CO oxidation electrocatalyzed by ∼2 nm dendrimer-encapsulated Pt nanoparticles (Pt DENs) is shifted negative by ∼300 mV in the presence of a small percentage (<2%) of Cu surface atoms. Theory and experiments suggest that the catalytic enhancement arises from a cocatalytic Langmuir-Hinshelwood mechanism in which the small number of Cu atoms selectively adsorb OH, thereby facilitating reaction with CO adsorbed to the dominant Pt surface. Theory suggests that these Cu atoms are present primarily on the (100) facets of the Pt DENs.

Ionic Liquid-Modified Electrocatalysts: The Interaction of [C1C2Im][OTf] with Pt(1 1 1) and its Influence on Methanol Oxidation Studied by Electrochemical IR Spectroscopy

Ionic liquids (ILs) have recently been proposed as modifying agents to tune the selectivity and the activity of electrocatalysts. In order to explore the origin of IL-induced effects on electrocatalytic reactions, we have investigated (i) the interaction of [C1C2Im][OTf]–water mixtures with Pt(111) single crystal electrodes and (ii) the influence of [C1C2Im][OTf] on methanol oxidation in acidic aqueous solution using cyclic voltammetry (CV) and electrochemical IR spectroscopy.We show that [C1C2Im][OTf] interacts strongly with the Pt(111) surface in the potential range from -0.2VAg/AgCl to 0.65VAg/AgCl, leading to partial blocking of the surface, partial suppression of hydrogen adsorption, and partial suppression of OHads formation. The interaction of the IL with Pt occurs in this potential range via specific adsorption of the [OTf]− anions which bind to Pt(111) via the SO3− group in a tilted adsorption geometry. The adsorption process is largely reversible as a function of the electrode potential, but shows a complex kinetics and becomes very slow at high IL coverage. Also, [C1C2Im][OTf] has a strong effect on the electro-oxidation of methanol in acidic solution. Adsorption of [OTf]− leads to partial blocking of the indirect oxidation pathway to CO. The onset potential for CO oxidation is found to be shifted to more positive values indicating hindered access of H2O to the electrode surface. CO and the [C1C2Im][OTf] form a mixed co-adsorption layer which is characterized by a strongly red-shifted CO stretching band. The effect is assigned to an IL-induced ligand effect in the mixed adsorbate layer and suggests that the direct modification of active centers by surface-bound IL species plays an important role in IL-modified electrocatalytic materials.

Enhanced Activity and Durability of Nanosized Pt-SnO2/IrO2/CNTs Catalyst for Methanol Electrooxidation.

Pt-SnO2/IrO2/CNTs anode catalyst for direct methanol fuel cell was designed and prepared with IrO2/CNTs as support for the subsequent immobilization of Pt and SnO2 at the same time. The structure of the catalysts and their catalytic performance in methanol electrooxidation were investigated and the roles of IrO2 and SnO2 in methanol electrooxidation were discussed as well. Results show that Pt-SnO2/IrO2/CNTs catalyst exhibits the best activity and durability for methanol electrooxidation when compared with Pt/CNTs, Pt/IrO2/CNTs and Pt-SnO2/CNTs. According to the results of electrochemical tests and physicochemical characterizations, the enhancements of Pt-SnO2/IrO2/CNTs were attributed to the special properties of IrO2 and SnO2, in which IrO2 mainly increases the methanol oxidation activity and SnO2 mainly improves the CO oxidation ability and durability. Therefore, Pt-SnO2/IrO2/CNTs exhibits excellent performance for methanol oxidation with higher electrocatalytic activity (I(f) of 1054 A g(Pt(-1)) and powerful anti-poisoning ability (the onset potential for CO oxidation of 0.3 V) and outstanding durability (the sustained time t in CP of 617 s), revealing a suitable anode catalyst for DMFCs.

Electrochemical Oxidation of the Carbon Support to Synthesize Pt(Cu) and Pt-Ru(Cu) Core-Shell Electrocatalysts for Low-Temperature Fuel Cells

The synthesis of core-shell Pt(Cu) and Pt-Ru(Cu) electrocatalysts allows for a reduction in the amount of precious metal and, as was previously shown, a better CO oxidation performance can be achieved when compared to the nanoparticulated Pt and Pt-Ru ones. In this paper, the carbon black used as the support was previously submitted to electrochemical oxidation and characterized by XPS. The new catalysts thus prepared were characterized by HRTEM, FFT, EDX, and electrochemical techniques. Cu nanoparticles were generated by electrodeposition and were further transformed into Pt(Cu) and Pt-Ru(Cu) core-shell nanoparticles by successive galvanic exchange with Pt and spontaneous deposition of Ru species, the smallest ones being 3.3 nm in mean size. The onset potential for CO oxidation was as good as that obtained for the untreated carbon, with CO stripping peak potentials about 0.1 and 0.2 V more negative than those corresponding to Pt/C and Ru-decorated Pt/C, respectively. Carbon oxidation yielded an additional improvement in the catalyst performance, because the ECSA values for hydrogen adsorption/desorption were much higher than those obtained for the non-oxidized carbon. This suggested a higher accessibility of the Pt sites in spite of having the same nanoparticle structure and mean size.

The role of non-covalent interactions on CO bulk oxidation on Pt single crystal electrodes in alkaline electrolytes

The role of non-covalent interaction between both non-specifically adsorbed hydrated K+, Li+ and Ba2+ cations (M+) and hydroxyl species (M+-OHad) as well as underpotentially deposited Cu adatoms and OHad (Cuupd-OHad) on bulk CO oxidation (COb) is investigated on Pt(111) and Pt(100) in alkaline solutions. The effect of Cuupd-OHad on COb oxidation is observed almost at the reversible potential for CO oxidation, signaling that Cuupd-induced adsorption of OHad activates COb oxidation at very low overpotentials. In contrast, the effect of M+-OHad was found to be strongly dependent on the surface coverage of OHad on Pt; e.g., while no effect is found when the surface is pre-covered by adsorbed CO (COad), a discernable effect is observed on OHad pre-covered Pt surface.

Electro-oxidation of formate-based solutions on Au/Pd core–shell nanoparticles – Experiment and simulation

Au/Pd core–shell nanoparticles (NPs) were employed to study electro-oxidation mechanism of formate-based solutions. A series of combined studies including Raman spectroscopy, electrochemical stripping analysis, and computational simulations were conducted to understand electro-oxidation of formate-based solutions on the Au/Pd NPs. Compared to the commercial Pd black, the Au/Pd NPs showed superior catalytic activities, especially when using concentrated formate solutions. CO stripping test in conjunction with in situ Raman studies showed a lower oxidation potential (0.6 V vs. Ag/AgCl) of CO on the Au/Pd NPs than the Pd black (>0.6 V). This indicated a strong electronic coupling between Au and Pd in the core–shell NPs which could enhance the oxidation of formate species. In addition, theoretical studies suggested lower formate and hydroxyl coverages at the same applied potential for the Au/Pd NPs than the Pd black in the formate-based solutions, shedding lights on their superior formate-oxidizing ability.

Hydrogenotitanates nanotubes supported platinum anode for direct methanol fuel cell

Hydrogenotitanates nanotubes (HTNs) are prepared from TiO2 powder via hydrothermal processing in 11.25 M NaOH aq. The reaction temperature is 130 °C for 20 h. Afterward a heat treatment is done during 2 h at 500 °C in air, to obtain calcined HTNs (HTNs-cal). The structural change on the molecular TiO2 during the hydrothermal treatment is investigated in detail by various analytic techniques such as XRD and TEM, which reveal that the crystal structure of the HTNs materials is similar to that of H2Ti2O5·H2O nanotubes with 160 nm in length and 10 nm in diameter. Nitrogen adsorption–desorption isotherms indicate that synthesized solids are mesoporous materials with a multiwalled nanotubular structure and high specific surface area. Platinum nanoparticles are deposited on the HTNs by the impregnation method for a total noble metal loading of 10 wt%. The electrocatalytic activity of these electrocatalysts is evaluated by cyclic voltammetry in acid medium. Typical CO stripping voltammetry in acidic solutions is investigated. The results demonstrate that the HTNs can greatly enhance the catalytic activity of Pt for methanol oxidation. The CO stripping test shows that the Pt/HTNs can shift the CO oxidation potential to lower direction than Pt/C (XC72) and Pt/HTNs-cal catalysts.

Effects of Pt Coverage in Pt@PdCu5/C Core–Shell Electrocatalysts on the Oxygen Reduction Reaction and Methanol Tolerance

Carbon-supported Pt@PdCu5 core–shell nanoparticles (Pt@PdCu5/C) with Pt contents from 14 to 49 atom % have been synthesized by first preparing the PdCu5/C cores by polyol reduction followed by an aqueous galvanic displacement reaction to obtain the Pt-rich shell. The effect of Pt coverage on oxygen reduction reaction and methanol tolerance was investigated. Pt surface enrichment has been confirmed by comparing the near surface to bulk metal composition. Initial cyclic voltammograms show less Cu dissolution from Pt@PdCu5/C with 49% Pt compared to samples with less Pt, consistent with estimates of Pt coverage. The methanol tolerance of the Pt@PdCu5/C series decreases with increasing Pt content as indicated by the negatively shifting CO oxidation potential. For Pt@PdCu5/C – 14% Pt, the positively shifted CO oxidation potential indicates the presence of surface Pd leading to increased methanol tolerance compared to Pt/C. Cu dissolution from Pt@PdCu5/C in the membrane-electrode assembly greatly affects the sin...

Characterization and performance evaluation of Pt–Ru electrocatalysts supported on different carbon materials for direct methanol fuel cells

Abstract The paper addresses the effect of the carbon support on the microstructure and performance of Pt–Ru-based anodes for direct methanol fuel cells (DMFC), based on the study of four electrodes with a carbon black functionalized with HNO3, a mesoporous carbon (CMK-3), a physical mixture of TiO2 and carbon black and a reference carbon thermally treated in helium atmosphere (HeTT). It is shown that CMK-3 hinders the growth of the electrocatalyst nanoparticles (2.7 nm) and improves their distribution on the support surface, whereas the oxidized surfaces of HNO3 carbon and TiO2+carbon lead to larger (4–4.5 nm), agglomerated particles, and the lowest electrochemical active areas (54 and 26 m2 g−1, in contrast with 90 m2 g−1 for CMK-3), as determined from CO stripping experiments. However, HNO3 and TiO2 are characterized by the lowest CO oxidation potential (0.4 V vs. RHE), thus suggesting higher CO tolerance for the se electrodes. Tests in DMFC configuration show that the three modified electrodes have clearly better performance than the reference HeTT. The highest power density attained with electrodes supported on carbon treated with HNO3 (65 mW cm−2/300 mA cm−2 at 90 °C) and the equally interesting performance of the TiO2-based electrodes (53 mW cm−2/300 mA cm−2), is a strong indication of the positive effect of the presence of oxygenated groups on the methanol oxidation reaction. The results are interpreted in order to identify separate microstructural (electrocatalyst particle size, porosity) and compositional (oxygenated surface groups, presence of oxide phase) effects on the electrode performance.

CO tolerance of proton exchange membrane fuel cells with Pt/C and PtMo/C anodes operating at high temperatures: A mass spectrometry investigation

The performance of proton exchange membrane fuel cells (PEMFC) with Pt/C and PtMo/C anodes has been investigated using single cell polarization and on line mass spectrometry (OLMS) measurements in a wide range of temperature (70–105°C) for the system supplied with hydrogen containing different amounts of CO. As expected a higher CO tolerance is observed at higher temperatures for both catalysts. The anode exit gas analysis revealed that CO2 is produced already at the cell open circuit potential, and it increases with the increase of the anode overpotential. The CO tolerance phenomena are assigned to different processes depending on the catalyst nature. For the Pt/C containing anodes, at temperatures above 80°C, thermal desorption, reduced CO oxidation potential and CO oxidation by O2 crossover are responsible for enhanced tolerance, whilst PtMo/C shows greater tolerance due the occurrence of a MoOx-mediated water gas shift reaction (WGS), which is activated at high temperatures. Although the occurrence of WGS leads to the anode poisoning in the presence of CO2, the polarization results show that only small additive contamination effect occurs by the combined presence of CO+CO2 in the hydrogen stream.

In situ FTIR studies of coadsorption of CN − and CO on Pt(1 1 0) electrode surface

The coadsorption of CN − and CO on Pt(1 1 0) electrode in acid solutions was investigated by using cyclic voltammetry and in situ FTIR spectroscopy. In comparison with individual adsorption of CO or CN −, the onset oxidation potential of CO (CO ad) coadsorbed with CN − is positively shifted ca. 100 mV, and its oxidation peak is postponed ca. 260 mV together with a significant decrease in current density. When the coadsorbed CO has been stripped completely, the CV recovers the feature of Pt(1 1 0)/CN − surface, which signifies that the coadsorption of CO does not affect the oxidation behavior of the coadsorbed CN − ( CN ad - ). In comparison of CN − and CO adsorbed alone, the CN ad - band is blue shifted from 2090 to 2108 cm −1 at 0.0 V, and the stark tuning rate is decreased dramatically from 53 to 4 cm −1 V −1; while the CO ad band is red shifted from 2075 to 2064 cm −1 at 0.0 V, and the stark tuning rate is slightly decreased from 24 to 19 cm −1 V −1, The result revealed the strong interaction between CN ad - and CO ad at Pt(1 1 0) surface in the coadsorption system.

Synthesis, Characterization of Nanostructured Rhodium Films and their Electrochemical Behavior towards Carbon Monoxide Oxidation

Rhodium nanostructured thin film catalysts were prepared by pulsed laser deposition. The depositions were performed under vacuum and at different He background gas pressures ranging from 1 to 5 Torr. SEM, TEM, X-ray diffraction, and X-ray photoelectron spectroscopy were used to evaluate the morphology, the structure, the surface composition, and the electronic structure of the catalysts. Their electrochemical properties were studied towards CO stripping measurements in acidic solution; a reaction of critical issue to liquid fuel cells. It was discovered that rhodium (Rh) film deposited under 5 Torr of He background pressure showed the highest electroactive surface area, and the lowest onset potential of CO oxidation demonstrating an enhancement of the CO poisoning resistance. The reason for such enhanced electrocatalytic activity is ascribed to the high porosity and roughness of the Rh surface. Compared to Pt films made under similar processing conditions (5 Torr of He), Rh film displayed higher roughness factor of 58.5 (vs. 30 for Pt), a net charge due to oxidation and desorption of the CO adlayer of 385 μC cm−2 (vs. 350 μC cm−2 for Pt), and an onset potential for CO oxidation of 30 mV less anodic than that at Pt electrode.

A New Strategy for Immobilization of Electroactive Species on the Surface of Solid Electrode

This letter reports on a new method for immobilization of electroactive species on a solid electrode surface based on the composite film of naphthol green B (NGB) and Co–Al layered double hydroxides (LDHs). After the oxidation potential of Co(III)/(II) couple was dramatically enhanced by NGB, the functionalized LDHs exhibited a remarkable electrocatalytic activity toward the oxidation of hydrazine in a weak acidic medium. The amperometric response to hydrazine showed a linear range of 0.17 μM–400 mM, with the calculated detection limit of 0.1 μM at a signal-to-noise ratio of three and the sensitivity of the amperometric hydrazine sensor was found to be 35.26 μA μM−1. The modified electrode displayed an acceptable reproducibility and good stability. The new strategy is expected to have wide applications for changing of the potential of redox couple in metal oxides, hydroxides, double hydroxides, and so on.

Highly Stable and CO-Tolerant Pt/Ti0.7W0.3O2 Electrocatalyst for Proton-Exchange Membrane Fuel Cells

The current materials used in proton-exchange membrane fuel cells (PEMFCs) are not sufficiently durable for commercial deployment. One of the major challenges lies in the development of an inexpensive, efficient, and CO-tolerant anode catalyst. Here we report the unique CO-tolerant property of Pt nanoparticles supported on Ti(0.7)W(0.3)O(2). The Ti(0.7)W(0.3)O(2) nanoparticles (50 nm) were synthesized via a sol-gel process and platinized using an impregnation-reduction technique. Electrochemical studies of Pt/Ti(0.7)W(0.3)O(2) show unique CO-tolerant electrocatalytic activity for hydrogen oxidation compared to commercial E-TEK PtRu/C catalysts. Differential electrochemical mass spectrometry measurements show the onset potential for CO oxidation on Pt/Ti(0.7)W(0.3)O(2) to be below 0.1 V (vs RHE). Pt/Ti(0.7)W(0.3)O(2) is a promising new anode catalyst for PEMFC applications.

The Evidences of Morphology Dependent Electroactivity Toward CO Oxidation over Bismuth Oxide Supported Pt

The new evidences of morphology dependent electrocatalytic activity for CO oxidation have been presented. Different morphological micro-sized Bi2O3 supports, with Bi2O3 flowers-like and tubes-like characteristics, have been synthesized. The Pt was deposited on the supports by photo-deposition method. It has been found that the micro-sized flowers-like supported Pt/Bi2O3 catalyst exhibits higher peak current densities, more negative onset potential, peak potential, and higher electrocatalytic activity for CO oxidation, compared with Pt/Bi2O3 microtubes. XRD and HR-TEM results indicate that there is a stronger interaction between Pt species and Bi2O3 flowers-like support. The new evidences of morphology dependent electrocatalytic activity for CO oxidation have been presented. It has been found that the micro-sized flowers-like supported Pt/Bi2O3 catalyst possess higher peak current densities, more negative onset potential, peak potential, and higher electrocatalytic activity for CO oxidation, compared with Pt/Bi2O3 microtubes.

A first principles comparison of the mechanism and site requirements for the electrocatalytic oxidation of methanol and formic acid over Pt

First principles density functional theoretical calculations were carried out to examine and compare the reaction paths and ensembles for the electrocatalytic oxidation of methanol and formic acid in the presence of solution and applied electrochemical potential. Methanol proceeds via both direct and indirect pathways which are governed by the initial C-H and O-H bond activation, respectively. The primary path requires an ensemble size of between 3-4 Pt atoms, whereas the secondary path is much less structure sensitive, requiring only 1-2 metal atoms. The CO that forms inhibits the surface at potentials below 0.66 V NHE. The addition of Ru results in bifunctional as well as electronic effects that lower the onset potential for CO oxidation. In comparison, formic acid proceeds via direct, indirect and formate pathways. The direct path, which involves the activation of the C-H bond followed by the rapid activation of the O-H bond, was calculated to be the predominant path especially at potentials greater than 0.6 V. The activation of the O-H bond of formic acid has a very low barrier and readily proceeds to form surface formate intermediates as the first step of the indirect formate path. Adsorbed formate, however, was calculated to be very stable, and thus acts as a spectator species. At potentials below 0.6 V NHE, CO, which forms via the non-Faradaic hydrolytic splitting of the C-O bond over stepped or defect sites in the indirect path, can build up and poison the surface. The results indicate that the direct path only requires a single Pt atom whereas the indirect path requires a larger surface ensemble and stepped sites. This suggests that alloys will not have the same influence on formic acid oxidation as they do for methanol oxidation.

Microfibrous Entrapped Catalysts for Low Temperature CO Oxidation

AbstractLow temperature CO oxidation is characterized by slow reaction kinetics and CO self-poisoning of the catalyst, which compete with each other. A platinum catalyst with ceria as a promoter supported on a high surface area silica support has been developed. The catalyst has a significant activity for CO oxidation even in the presence of moisture. The catalyst showed a significant increase in activity with decreasing particle size (η&lt;0.95, even at 100μm), indicating a clear transport limitation.In case of larger catalyst particles the diffusional resistances affect the reaction kinetics, leading to greater rates of CO self-poisoning causing deactivation of the catalysts. However, conventional packed bed of smaller particles poses problems such as high pressure drop, packing issues, bed channeling, flow maldistributions, and dead zones in the reactor bed, which result in poor inter-phase heat and mass transfer rates. Most of these problems are related to poor packaging of smaller particles, strongly suggesting the need for immobilization of small particles. A new class of micro-structured materials consisting of sorbents/catalysts entrapped in metal, ceramic, or polymer microfibers (MFES/MFEC) has been developed at Auburn University. These materials immobilize the small particles by sinter-locking them in fiber mesh. The immobilization of particles results in better heterogeneous contacting efficiency. Additional studies have shown that the high voidages and structural uniformity of the MFES lowered the flow maldistributions, eliminated the peaking flows between particles, and helped achieve better radial dispersion. Thus MFEC/MFES improved inter-phase transport rates.The Pt-CeO2/SiO2 catalyst entrapped in metal microfibers demonstrated a significant improvement in CO conversion compared to a conventional packed bed configuration while maintaining a lower pressure drop. Further catalyst entrapment in metal microfibers minimized cold spots in the reactor bed due to better intra-phase heat transfer rate. Higher effective thermal conductivity of MFEC improved the activity of the catalyst, which was particularly visible at high CO concentration wherein the CO inhibition kinetics takes over. For example, MFEC with 1/3 rd of catalyst loading as that of packed bed of same particle size, outperformed packed bed configuration.The catalysts were prepared by incipient wet impregnation. Surface characterization of catalysts was carried out using CO, H2, O2 chemisorption, O2 – H2 titration, N2 physisorption, powder XRD, and was correlated with catalytic activity.This microfibrous entrapped catalyst demonstrated a great potential for low temperature CO oxidation. These MFEC can be used in air purification, emergency escape products, and as a cathode air filter for PEM fuel cells.

Effect of carbon substrate materials as a Pt–Ru catalyst support on the performance of direct methanol fuel cells

The support effect of carbon nanotubes (CNTs) for direct methanol fuel cell (DMFC) was studied using CNTs with and without defect preparation, carbon black, and fishbone-type CNTs. The Pt–Ru/defect-free CNTs afforded the highest catalytic activity of methanol oxidation reaction (MOR) in rotating disk electrode experiments and the highest performance as the anode catalysts in DMFC single cell tests with the one-half platinum loading compared to Pt–Ru/VulcanXC-72R. CO stripping voltammograms with Pt–Ru/defect-free CNTs also revealed the lowest CO oxidation potential among other Pt–Ru catalysts using different carbon support. It is thus considered that the carbon substrates significantly affect the CO oxidation activity of anode electrocatalysts in DMFC. This is ascribed to the geometrical effect that the flat interface between CNTs and metal catalysts has a unique feature, at which the electron transfer occurs, and this interface would modify the catalytic properties of Pt–Ru particles.

Carbon monoxide and methanol oxidation at platinum catalysts supported on ordered mesoporous carbon: the influence of functionalization of the support

The influence of different functionalization treatments of the support on the electrocatalytic activity towards CO and methanol oxidation at platinum nanoparticles deposited on ordered mesoporous carbons (OMC) has been studied for the first time. Before deposition of the metal, the carbon support was functionalized applying several procedures, with the purpose to generate oxygenated groups for anchoring the Pt nanoparticles by the formic acid (FM) and borohydride (BM) reduction methods. Good dispersion of the catalyst was obtained in all cases. It has been shown that particle size, and consequently the lattice parameter and metal surface area, depends on the functionalization treatment employed. CO and methanol electrooxidation was studied at all prepared catalysts applying cyclic voltammetry. It was observed that CO stripping occurs at more negative potentials (around 0.10-0.15 V) with these supports with respect to Vulcan XC-72 supported catalysts, and the best results for both methods were achieved with OMC functionalized with concentrated nitric acid for 0.5 h. This carbon support presents a higher amount of oxygenated groups without the loss of the ordered structure. In situ infrared studies have been performed for the first time with this type of catalyst, showing that the effect of the carbon support on the CO oxidation potential is similar to the presence of a second metal as Ru under the same experimental conditions. Methanol electrooxidation is also dependent on the nature of the support, as proved from both cyclic voltammetry and chronoamperometry. In this case, results depend on the method of nanoparticles preparation and seem to be better for BM.