Electrocatalytic Oxidation Of CO Research Articles

Toward understanding CO oxidation on high-entropy alloy electrocatalysts

Extended high-entropy alloy electrocatalysts as a platform to investigate electrocatalytic CO oxidation and surface structure–property relations.

Self-Standing Pd-Based Nanostructures for Electrocatalytic CO Oxidation: Do Nanocatalyst Shape and Electrolyte pH Matter?

Tailoring the shape of Pd nanocrystals is one of the main ways to enhance catalytic activity; however, the effect of shapes and electrolyte pH on carbon monoxide oxidation (COOxid) is not highlighted enough. This article presents the controlled fabrication of Pd nanocrystals in different morphologies, including Pd nanosponge via the ice-cooling reduction of the Pd precursor using NaBH4 solution and Pd nanocube via ascorbic acid reduction at 25 °C. Both Pd nanosponge and Pd nanocube are self-standing and have a high surface area, uniform distribution, and clean surface. The electrocatalytic CO oxidation activity and durability of the Pd nanocube were significantly superior to those of Pd nanosponge and commercial Pd/C in only acidic (H2SO4) medium and the best among the three media, due to the multiple adsorption active sites, uniform distribution, and high surface area of the nanocube structure. However, Pd nanosponge had enhanced COOxid activity and stability in both alkaline (KOH) and neutral (NaHCO3) electrolytes than Pd nanocube and Pd/C, attributable to its low Pd-Pd interatomic distance and cleaner surface. The self-standing Pd nanosponge and Pd nanocube were more active than Pd/C in all electrolytes. Mainly, the COOxid current density of Pd nanocube in H2SO4 (5.92 mA/cm2) was nearly 3.6 times that in KOH (1.63 mA/cm2) and 10.3 times that in NaHCO3 (0.578 mA/cm2), owing to the greater charge mobility and better electrolyte-electrode interaction, as evidenced by electrochemical impedance spectroscopy (EIS) analysis. Notably, this study confirmed that acidic electrolytes and Pd nanocube are highly preferred for promoting COOxid and may open new avenues for precluding CO poisoning in alcohol-based fuel cells.

Electrocatalytic CO oxidation on porous ternary PdNiO-CeO2/carbon black nanocatalysts: Effect of supports and electrolytes

The catalytic activity and durability of porous ternary Pd-based electrocatalysts are augmented by alloying with other metals and using supports, however, the effect of supports and electrolytes at varied pH on the electrochemical CO oxidation (COOxid) performance is not yet studied. Herein, a PdNiO-CeO2/CB nanosphere, composed of PdNiO nanocrystals sprouted on CeO2 flake-like and carbon black (CB) nanosheets, was synthesized by a sol-gel and impregnation methods. Remarkably, during the impregnation step, CeO2/CB serves as a reactor for the reduction of Pd/Ni precursors and supported the growth of PdNiO nanocrystals without surfactant and/or reducing agent. This endowed the formation of PdNiO-CeO2/CB with multifunctional porous structures, including pore volume (0.29 cm3/g) and specific surface area (151.86 m2/g) and a clean Pd surface. The as-prepared PdNiO-CeO2/CB delivers a superior COOxid activity than those of PdNiO-CeO2, PdNiO/CB, and commercial Pd/C in acidic (HClO4), neutral (NaHCO3), and alkaline (KOH) electrolytes, ascribable to the oxygen-enriched support (CeO2) and its interaction with CB support along with electronic effect of PdNiO, which enhances the CO adsorption/activation and simultaneously activates/splits H2O to produce active oxygenated species required for hastening COOxid kinetics. Interestingly, the COOxid performance of the PdNiO-CeO2/CB in HClO4 electrolyte was higher than those in NaHCO3 and KOH electrolytes. This study reveals that coupling oxygen-enriched support (CeO2) with CB support is preferred for the enhancement of the COOxid activity of PdNiO nanocrystals.

EFEITO DOS DEFEITOS DE SUPERFÍCIE E DO pH NA ADSORÇÃO E NA CATÁLISE DA ELETRO-OXIDAÇÃO DE CO EM SUPERFÍCIES MODELOS DE PLATINA

SURFACE DEFECTS AND pH EFFECTS ON ADSORPTION AND CATALYSIS OF CO ELECTRO-OXIDATION ON MODEL PLATINUM SURFACES. Platinum is one of the well-known catalytic materials for which the electro-oxidation of carbon monoxide better behaves as a sensitive reaction to the catalyst surface structure. For the electro-catalytic reactions that behave like this, the rate (faradaic current density) is the result of the sum of the activity of the different active sites working with very different efficiencies or abilities. In this scenario, different atomic arrangements on the catalyst surface are expected to play different roles in surface-catalyzed reactions. In this article, the functionalities that surface defects (steps) can play in the adsorption and electrocatalytic oxidation of CO on model platinum surfaces are reviewed. Surface defects are indirectly related to the up catalysis as well as to the inhibition of reaction pathways of CO electro-oxidation under very particular conditions; these surface entities are also indirectly related to restrictions for the mobility of adsorbed CO on the (111) terraced surfaces. We analyze the selective activation and deactivation of surface sites by the pH effect, and typical catalytic properties of extended surfaces and shaped-controlled nanoparticles have been discussed thoroughly. We present a model of most active sites involved in the pathways of CO2 formation from the electro-oxidation of adsorbed CO.

Pd/Ni-metal-organic framework-derived porous carbon nanosheets for efficient CO oxidation over a wide pH range.

Metal nanocrystal ornamented metal-organic frameworks (MOFs) are of particular interest in multidisciplinary applications; however, their electrocatalytic CO oxidation performance over wide pH ranges is not yet reported. Herein, Ni-MOF-derived hierarchical porous carbon nanosheets (Ni-MOF/PC) with abundant Ni-N x sites decorated with Pd nanocrystals (Pd/Ni-MOF/PC) were synthesized by microwave-irradiation (MW-I) followed by annealing at 900 °C and subsequent etching of Ni-MOF/C prior to Pd deposition. The fabrication mechanism comprises the generation of self-reduced reducing gases from triethylamine during the annealing and selective chemical etching of Ni, thereby facilitating the reduction of Ni-anchored MOF and Pd nanocrystal deposition with the aid of ethylene glycol and MW-I to yield Pd/Ni-N x enriched MOF/PC. The synthetic strategies endear the Pd/Ni-MOF/PC with unique physicochemical merits: abundant defects, interconnected pores, high electrical conductivity, high surface area, Ni-deficient but more active sites for Pd/Ni-N x in porous carbon nanosheets, and synergism. These merits endowed the CO oxidation activity and stability on Pd/Ni-MOF/PC substantially than those of Pd/Ni-MOF/C and Pd/C catalysts in wide pH conditions (i.e., KOH, HClO4, and NaHCO3). The CO oxidation activity study reveals the utilization of MOF/PC with metal nanocrystals (Pd/Ni) in CO oxidation catalysis.

A comparative study of CO catalytic oxidation on the single vacancy and di-vacancy graphene supported single-atom iridium catalysts: A DFT analysis

Engineering of high-performance catalysts is of great importance for reducing the greenhouse gas emission by the electrocatalytic oxidation of CO. Single-atom-catalysts (SACs) have gained substantial attention thanks to their superior catalytic activity for CO oxidation, and graphene has been considered as one most promising supporting material owing to its peculiar physicochemical properties. In this work, the mechanism of CO oxidation over iridium (Ir) embedded on both single vacancy graphene (Ir-GNSV) and di-vacancy graphene (Ir-GNDV) has been investigated with the aid of density functional theory (DFT). The structural properties of Ir-GNSV and Ir-GNDV were analyzed by Bader charge analysis and electron density difference map. The calculated adsorption energy values of CO and O2 molecules on both the Ir-GNSV and Ir-GNDV have validated that both molecules can be molecularly adsorbed on the surface of each catalyst at room temperature. The results put forth that the reaction mechanism of CO + O2 → OOCO → CO2 + O* prefers to Langmuir − Hinshelwood (LH) mechanism. The activation energy for the transition-state for Ir-GNSV has been calculated to be 0.31 eV, whereas the first transition state (TS1) and the second transition state (TS2) of Ir-GNDV have been determined as 0.30 eV and 0.26 eV, respectively. Moreover, the results have confirmed that Ir-GNSV and Ir-GNDV surfaces have high catalytic activity and selectivity towards CO oxidation. On the basis of these findings, the proposed Ir-GNSV and Ir-GNDV catalysts are considered to be promising SAC for CO oxidation at low-temperature. It can be speculated that this work paves the way for the engineering of boosted-performance Ir-based heterogeneous catalysts by providing deeper mechanistic insights.

Generation of active Co(III) and peroxodiphosphate by synergistic electrocatalytic system with phosphate and the mediator cobalt(II) and its degradation performance.

The promising synergistic electrocatalytic system of phosphate (PO43-) with the mediator cobalt(II) (for short E-Co(II)-PO43-) was employed to degrade cationic dye methylene blue (MB). The exploration in the electrocatalytic process revealed that the main intermediate active oxidation products were Co(III), accompanied with hydroxyl radicals and peroxodiphosphates (P2O84-). Their synergistic electrocatalytic degradation rate to MB and total organic carbon (TOC) was up to 100 and 60% in 40 min, respectively, which was 5 times and 2.6 times that in a direct electrocatalytic system, correspondingly. The degradation process of the E-Co(II)-PO43- system on MB started with the bond being broken at the N-C junction of the MB molecule and intermediate active oxidation substances being generated, such as phenothiazine, 2-amino-5-(N-methylformamide) benzene sulfonic acid and N1,N1-dimethyl-1,4 diaminobenzene. Then, the intermediates were degraded into aniline, phenol and benzene sulfonic acid, and eventually decomposed into inorganic substances like CO2 and water. The electrocatalytic degradation mechanism of E-Co(II)-PO43- system on MB was the combination of indirect oxidation of the intermediate oxidants like Co(III), P2O84- and the hydroxyl radical with direct electrocatalysis on the platinum titanium electrode, where the electrocatalytic oxidation of Co(III) was dominant.

(Invited) Electrooxidation of Urea and Creatinine on a Nickel Electrocatalyst

Urea is one of the world’s most abundant waste products, commonly found in waste streams in varying concentrations. Urea is the compound in largest abundance in human urine (other than water), and creatinine is its second most abundant organic compound [1]. Typical concentrations of urea and creatinine in human urine are 0.22 M and 0.013 M, respectively. In treatment of human and animal urine streams, a method for reactive removal of organic compounds must include elimination of both urea and creatinine. A previous study by Schrank et al. [2] of the electrochemistry of urine compounds showed that, on a nickel cobaltite catalyst at urine-relevant concentrations, creatinine suppressed the reaction of urea at lower potentials, while creatinine oxidized preferentially over urea at higher potentials. In dialysate, however, urea and creatinine are present in lower concentration, typically 6 mM and 60 μM, respectively, and whether co-reaction of a urea/creatinine solution occurs is of strong interest in removal of uremic toxins.Electrochemical reaction of urea has been studied for a variety of electrodes and is currently receiving increased interest due to its potential in treating wastewater to produce hydrogen and ammonia [3–5]. Urea electrooxdiation is also suitable for a direct urea fuel cell [6]. To date, one of the most active electrodes is Ni(OH)2, which converts to the catalytically active (Ni3+) form of nickel oxyhydroxide (NiOOH) above 0.45 V vs. a Hg/HgO electrode at pH 14 [3]. Urea electrooxidation is a 6-electron process; the anode reaction in alkaline media is(NH2)2CO + 6 OH− → N2 + CO2 + 5 H2O + 6 e − and has a standard potential of −0.896 VHg/HgO (0.070 VRHE) at pH 14. Electrooxidation of creatinine is a 21-electron processC4H7N3O + 21 OH− → 3/2 N2 + 4 CO2 + 14 H2O + 21 e − and has a standard potential of −1.021 VHg/HgO (−0.055 VRHE) at pH 14. Materials and Methods Cyclic voltammetry (CV) and chronoamperometry were performed in a three-electrode cell (Pine electrochemistry) utilizing a Pt coil counter electrode (CE) and a Hg/HgO reference electrode (RE) appropriate for alkaline solutions. The working electrode (WE) for each experiment was either a polished Ni disk (Basi), Ni hydroxy foam (NHF), or NHF with 1% Fe (NHF-Fe). All solutions contained 1 M KOH as a supporting electrolyte, chosen to represent the strongly alkaline environment of an anion exchange membrane that would be used in a larger reaction cell. Urea and creatinine were added in concentration ranges typical of healthy and uremic human serum. Data collection and visualization were performed with a Solartron 1287A potentiostat coupled with CorrWare/CorrView software. All cyclic voltammetry was performed at a scan rate of 10 mV/s. Results Figure 1 shows CVs of blank solution, urea solution, and a urea/creatinine solution on a NHF-Fe electrode. The Ni2+/Ni3+transition [Ni(OH)2 + OH− ↔ NiOOH + H2O + e −] occurs over the range of 0.45–0.6 VHg/HgO for oxidation and 0.2–0.55 VHg/HgO for reduction. The oxygen evolution reaction (OER) occurs at potentials of 0.65 VHg/HgO and higher. Urea oxidation (in 10 mM urea) occurs over the range of 0.5–0.65 VHg/HgO , and its overlap with the Ni2+/Ni3+ transition demonstrates the catalytic nature of Ni3+. These results are in agreement with previous work. When 59 μM creatinine was added, the CV shows an increased oxidation peak in the urea oxidation region, attributed to co-oxidation of urea and creatinine. Chronoamperometry results (not shown) show that steady-state oxidation is established within one minute at 0.55 VHg/HgO. The steady-state oxidation current was 15 mA/cm2 for the urea/creatinine solution vs. 12 mA/cm2 for urea alone. Conclusion Electrocatalytic co-oxidation of urea and creatinine occur on a NHF-Fe electrode in alkaline (pH 14) media at potentials of 0.5–0.65 VHg/HgO. Demonstration of co-oxidation is of primary importance in reactive removal of organic compounds from dialysate and – by extension – from urine. Acknowledgements This work was supported by the University of Washington.

Mechanistic Analysis of Electrocatalytic CO Oxidation By a Rh Porphyrin on a Carbon Support

Electrochemical CO oxidation (CO + H2O → CO2 + 2H+ + 2e–) is important to counteract CO poisoning of Pt-based anode catalysts, since the reaction can reduce CO concentration on an anode of PEFC. However, the CO oxidation at anode potentials hardly occurs on conventional Pt-Ru electrocatalysts. From these backgrounds, we have developed Rh-porphyrin-based electrocatalysts for CO oxidation [1, 2]. In the catalysts, molecules of Rh porphyrin are dispersed on a carbon black support. These catalysts can oxidize CO at much lower overpotentials than the Pt-Ru electrocatalysts [1-3]. A membrane-electrode assembly (MEA) that uses a Rh porphyrin as an anode catalyst gave significant power (>40 mW/cm2) when CO was supplied as a fuel [4]. A combined catalyst of a Rh porphyrin and Pt-Ru catalyst functions as a CO-tolerant anode catalyst [5]. However, the reason why Rh porphyrins can catalyze CO electro-oxidation at low overpotentials remains unclear. Mechanistic analyses on carbon-supported Rh porphyrin are needed to clarify the reason. The analysis would also contribute to further improvement of this catalyst. In this work, we report a possible reaction mechanism of CO oxidation by the catalyst. First, we examined the reactivity of Rh porphyrins dissolved in solution. This analysis enables us to discuss the CO activation mechanism by Rh porphyrins without the effect of carbon black support. A Rh porphyrin was treated with CO gas in dichloromethane to generate CO adduct of the Rh porphyrin. We characterize this CO-adduct, a possible intermediate of CO oxidation, by IR, NMR, and X-ray crystallography. The results indicate that CO coordinated on Rh atom is feasible to nucleophilic attack by water. Actually, the CO-adduct reduces an soluble electron acceptor in the presence of water. A possible reaction mechanism is shown in Fig. 1. An electrode works as an electron acceptor in the electrocatalytic CO oxidation. In actual electroctalysts using Rh porphyrins, molecules are adsorbed on a carbon black support. Configuration of molecules on a carbon support would be also important for the catalytic activity. Then, we examined possible effects of the configuration by observing molecules on a highly oriented pyrolytic graphite with an atomic force microscope. The results show that certain ligand structure facilitates the configuration desirable for the high catalytic activity. These analyses would be an answer for the question; why does Rh porphyrin can oxidize CO at lower potentials than conventional Pt-based catalysts. This work was supported by Grant-in-Aids for Scientific Research (B) (No. 15H03853).

Removal of CO from CO-contaminated hydrogen gas by carbon-supported rhodium porphyrins using water-soluble electron acceptors

Abstract Carbon-supported Rh porphyrins catalyze the oxidation of carbon monoxide by water-soluble electron acceptors. The rate of this reaction is plotted as a function of the redox potential of the electron acceptor. The rate increases with an increase in the redox potential until it reaches a plateau. This profile can be explained in terms of the electrocatalytic CO oxidation activity of the Rh porphyrin. The removal of CO from CO(2%)/H2 by a solution containing a carbon-supported Rh porphyrin and an electron acceptor is examined. The complete conversion of CO to CO2 is achieved with only a slight amount of Rh porphyrins. Rh porphyrin on carbon black gives higher conversion than that dissolved in solution. This reaction can be used not only to remove CO in anode gas of stationary polymer electrolyte fuel cells but also to regenerate a reductant in indirect CO fuel cell systems.

Disentangling Catalytic Activity at Terrace and Step Sites on Selectively Ru-Modified Well-Ordered Pt Surfaces Probed by CO Electro-oxidation

In heterogeneous (electro)catalysis, the overall catalytic output results from responses of surface sites with different catalytic activities, and their discrimination in terms of what specific site is responsible for a given activity is not an easy task. Here, we use the electro-oxidation of CO as a probe reaction to access the catalytic activity of different sites on high-Miller index stepped Pt surfaces with their {110} steps selectively modified by Ru at different coverages. Data from in situ Fourier transform infrared spectroscopy and cyclic voltammetry evidence that Ru deposited on {110} steps modifies the surface in a nontrivial way, favoring only the electrocatalytic oxidation of CO over {111} terraces. Moreover, these {111} terraces become catalytically active throughout a large potential window. On the other hand, after the deposition of Ru on {110} steps, the partial oxidation of a CO adlayer (by stripping voltammetry and in situ FTIR potential steps) shows that those {110} steps that remain fr...

Unusual Activity Trend for CO Oxidation on Pd(x)Au(140-x)@Pt Core@Shell Nanoparticle Electrocatalysts.

A theoretical and experimental study of the electrocatalytic oxidation of CO on PdxAu140-x@Pt dendrimer-encapsulated nanoparticle (DEN) catalysts is presented. These nanoparticles are comprised of a core having an average of 140 atoms and a Pt monolayer shell. The CO oxidation activity trend exhibits an unusual koppa shape as the number of Pd atoms in the core is varied from 0 to 140. Calculations based on density functional theory suggest that the koppa-shaped trend is driven primarily by structural changes that affect the CO binding energy on the surface. Specifically, a pure Au core leads to deformation of the Pt shell and a compression of the Pt lattice. In contrast, Pd, from the pure Pd cores, tends to segregate on the DEN surface, forming an inverted configuration having Pt within the core and Pd in the shell. With a small addition of Au, however, the alloy PdAu cores stabilize the core@shell structures by preventing Au and Pd from escaping to the particle surface.

A One-Pot Approach to Mesoporous Metal Oxide Ultrathin Film Electrodes Bearing One Metal Nanoparticle per Pore with Enhanced Electrocatalytic Properties

The controlled incorporation of single metal nanoparticles within the pores of mesostructured conducting metal oxide ultrathin films is demonstrated, taking advantage of the controlled metal precursor loading capacities of PS-b-P4VP inverse micellar templates. The presented one-pot approach denoted as Evaporation-Induced Hydrophobic Nanoreactor Templating (EIHNT) unusually involves the nanostructuration of the metal oxide via the hydrophobic shell of the micellar template, while the concomitant nanostructuration of the metal is achieved via its confinement in the hydrophilic micellar core. This approach is applied to tin-rich ITO and gold, to yield unique mesoporous tin-rich ITO ultrathin film electrodes remarkably loaded with one size-controlled gold nanoparticle per pore. Interestingly, the resulting tin-rich ITO-supported gold nanoparticles exhibit improved catalytic activity and durability in electrocatalytic CO oxidation compared to similarly sized gold nanoparticles supported on conventional ITO coatings.

Long-Range Segregation Phenomena in Shape-Selected Bimetallic Nanoparticles: Chemical State Effects

A study of the morphological and chemical stability of shape-selected octahedral Pt0.5Ni0.5 nanoparticles (NPs) supported on highly oriented pyrolytic graphite (HOPG) is presented. Ex situ atomic force microscopy (AFM) and in situ X-ray photoelectron spectroscopy (XPS) measurements were used to monitor the mobility of Pt0.5Ni0.5 NPs and to study long-range atomic segregation and alloy formation phenomena under vacuum, H2, and O2 environments. The chemical state of the NPs was found to play a pivotal role in their surface composition after different thermal treatments. In particular, for these ex situ synthesized NPs, Ni segregation to the NP surface was observed in all environments as long as PtOx species were present. In the presence of oxygen, an enhanced Ni surface segregation was observed at all temperatures. In contrast, in hydrogen and vacuum, the Ni outward segregation occurs only at low temperature (<200-270 °C), while PtOx species are still present. At higher temperatures, the reduction of the Pt oxide species results in Pt diffusion toward the NP surface and the formation of a Ni-Pt alloy. A consistent correlation between the NP surface composition and its electrocatalytic CO oxidation activity was established.

일산화탄소 산화를 위한 PtRu/C 시리즈 촉매의 합성 및 특성 연구

The electrocatalytic oxidation of CO was studied using carbon-supported 20 wt% PtRu (PtRu/C) catalysts, which were prepared with different Pt : Ru atomic ratios from 7 : 3 to 3 : 7 using a colloidal method combined with a freeze-drying procedure. The bimetallic PtRu/C catalysts were characterized by various physicochemical analyses, including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). CO stripping voltammetry measurements indicated that the addition of Ru with a Pt catalyst significantly improved the electrocatalytic activity for CO electrooxidation. Among the tested catalysts, the Pt5Ru5/C catalyst had the lowest onset potential (vs.Ag/AgCl) and the largest CO EAS. Structural modification via lattice parameter change and electronic modification in the unfilled d band states for Pt atoms may facilitate the electrooxidation of CO.

Preparation of Pt nanoparticles supported on ordered mesoporous carbon FDU-15 for electrocatalytic oxidation of CO and methanol

In this work, we proposed an improved wet-chemical method to synthesize Platinum (Pt) nanoparticles supported on the mesoporous carbon (FDU-15). A well-dispersed Pt precursor in FDU-15 was first received by using a CH2Cl2 solvent process and a simple melt-diffusion strategy. After the Pt precursor was reduced by formic acid without surfactant, almost 100% Pt nanoparticles were confined in the channels of FDU-15 (denoted as Pt/FDU-15). Physical (XRD, HRTEM and BET) and electrochemical (Cyclic voltammetry, COad stripping and chronoamperometry) methods were used to investigate the properties of Pt/FDU-15. Compared with the commercial catalyst Pt/C, the Pt/FDU-15 catalyst exhibits a much higher electrocatalytic activity toward CO and methanol oxidation. The origins of the high electrocatalytic activity of the Pt/FDU-15 were discussed.

Electrocatalytic Oxidation of CO at Pt Modified with Manganese Oxide Nanorods

CO oxidation at Pt anodes modified with manganese oxide nanorods (nano-MnOx/Pt) has been studied by cyclic and linear sweep voltammetry. Both CO adlayer stripping and oxidation of bulk CO are enhanced by nano-MnOx as compared to unmodified Pt electrodes. This is manifested by a negative shift of approximately 200 mV in the peak potential of CO adlayer stripping at the modified compared to the unmodified Pt surface. This enhancement is attributed to the catalytic mediation of manganese oxide nanorods (electrodeposited in a γ-MnOOH single crystalline phase), which supplies oxygen species at relatively low anodic potentials and thus facilitates the oxidation of CO to CO2. This finding sheds new light on the formic acid oxidation in the presence of MnOx, as the latter can remove CO efficiently from the Pt surface, and hence, prevents its de-activation.

Interaction of Mass Transport and Reaction Kinetics during Electrocatalytic CO Oxidation in a Thin-Layer Flow Cell

The interplay between electrocatalytic CO oxidation kinetics and mass transport in a thin-layer flow cell with a polycrystalline platinum electrode was experimentally studied and numerically simulated. The experiments were performed in a flow cell under controlled electrolyte flow. The computations are based on four different models for mass transport, coupled with a three-step reaction mechanism for CO oxidation that includes surface coverage effects. A zero-dimensional model neglecting mass transport effects on the overall reaction rate is applied to verify the effect of the kinetic parameters on the Faradaic current qualitatively. Transport models of increasing complexity, one-, two-, and three-dimensional, are used to analyze the impact of diffusion and convection on the total reaction rate in the flow cell. The numerical simulation, based on a time-resolved three-dimensional transport model coupled with the electrocatalytic kinetics, resolves profiles of temporal and spatial concentrations, velocities, and surface coverages. Mass transfer limitations of the electrocatalytic reaction rate are primarily caused by CO diffusion normal to the electrode. Both the two- and the three-dimensional models can quantitatively predict the Faradaic current as a function of potential measured in the experimental setup.

In situ X‐ray Absorption Analysis of ∼1.8 nm Dendrimer‐Encapsulated Pt Nanoparticles during Electrochemical CO Oxidation

We report an in situ X-ray absorption-fine structure (XAFS) spectroscopic analysis of ∼1.8 nm Pt dendrimer-encapsulated nanoparticles (DENs) during electrocatalytic oxidation of CO. The results indicate that Pt nanoparticles encapsulated within poly(amidoamine) (PAMAM) dendrimers and immobilized on a carbon electrode retain their electrocatalytic activity and are structurally stable for extended periods during CO oxidation. This is a significant finding, because nanoparticles in this size range are good experimental models for comparison to first-principles calculations if they remain stable.

Structural Properties of Unsupported Pt−Ru Nanoparticles as Anodic Catalyst for Proton Exchange Membrane Fuel Cells

The structural properties of the nanoparticles of a high-performance commercial unsupported Pt−Ru electrocatalyst with a nominal equiatomic relationship have been studied. They were exhaustively determined by transmission electron microscopy (TEM), high-resolution TEM, fast Fourier transform, electron diffraction, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) techniques. TEM and its coupled techniques showed that polyoriented Pt−Ru nanoparticles present an average size of 3.0 ± 0.5 nm with nondetection of metal oxides. XPS spectra, however, indicate the existence of oxidized Pt and Ru species. In particular, the proton- and electron-conducting hydrous Ru oxide involved in the electrocatalytic oxidation of CO and methanol is detected. XRD confirmed that a Pt−Ru solid solution with a 41 at.% Ru is the main crystallographic phase in the electrocatalyst, whereas Pt and Ru oxides appear to be amorphous or very thin. The strain corrected Williamson−Hall models confirmed that nanoparticles ...