Good CO Tolerance Research Articles

Hexa‐atom Pt Catalyst Fabricated by a Ligand Engineering Strategy for Efficient Hydrogen Oxidation Reaction

AbstractAtomically precise supported nanocluster catalysts (APSNCs), which feature exact atomic composition, well‐defined structures, and unique catalytic properties, offer an exceptional platform for understanding the structure‐performance relationship at the atomic level. However, fabricating APSNCs with precisely controlled and uniform metal atom numbers, as well as maintaining a stable structure, remains a significant challenge due to uncontrollable dispersion and easy aggregation during synthetic and catalytic processes. Herein, we developed an effective ligand engineering strategy to construct a Pt6 nanocluster catalyst stabilized on oxidized carbon nanotubes (Pt6/OCNT). The structural analysis revealed that Pt6 nanoclusters in Pt6/OCNT were fully exposed and exhibited a planar structure. Furthermore, the obtained Pt6/OCNT exhibited outstanding acidic HOR performances with a high mass activity of 18.37 A ⋅ mgpt−1 along with excellent stability during a 24 h constant operation and good CO tolerance, surpassing those of the commercial Pt/C. Density functional theory (DFT) calculations demonstrated that the unique geometric and electronic structures of Pt6 nanoclusters on OCNT altered the hydrogen adsorption energies on catalytic sites and thus lowered the HOR theoretical overpotential. This work presents a new prospect for designing and synthesizing advanced APSNCs for efficient energy electrocatalysis.

Hexa-atom Pt Catalyst Fabricated by a Ligand Engineering Strategy for Efficient Hydrogen Oxidation Reaction.

Atomically precise supported nanocluster catalysts (APSNCs), which feature exact atomic composition, well-defined structures, and unique catalytic properties, offer an exceptional platform for understanding the structure-performance relationship at the atomic level. However, fabricating APSNCs with precisely controlled and uniform metal atom numbers, as well as maintaining a stable structure, remains a significant challenge due to uncontrollable dispersion and easy aggregation during synthetic and catalytic processes. Herein, we developed an effective ligand engineering strategy to construct a Pt6 nanocluster catalyst stabilized on oxidized carbon nanotubes (Pt6/OCNT). The structural analysis revealed that Pt6 nanoclusters in Pt6/OCNT were fully exposed and exhibited a planar structure. Furthermore, the obtained Pt6/OCNT exhibited outstanding acidic HOR performances with a high mass activity of 18.37 A ⋅ mgpt -1 along with excellent stability during a 24 h constant operation and good CO tolerance, surpassing those of the commercial Pt/C. Density functional theory (DFT) calculations demonstrated that the unique geometric and electronic structures of Pt6 nanoclusters on OCNT altered the hydrogen adsorption energies on catalytic sites and thus lowered the HOR theoretical overpotential. This work presents a new prospect for designing and synthesizing advanced APSNCs for efficient energy electrocatalysis.

Modulating the synergy of Pd@Pt core–shell nanodendrites for boosting methanol electrooxidation kinetics

The single-pot production of Pd@Pt core–shell structures is a promising approach as it offers large surface area, catalytic capability, and stability. In this work, we established a single-pot process to produce Pd@Pt core–shell nanodendrites with tunable composition, shape and size for optimal electrochemical activity. Pd@Pt nanodendrites with diverse compositions were synthesized by tuning the ratios of Pd and Pt sources in an aqueous environment using cetyltrimethylammonium chloride, which functioned as both the surfactant and the reducing agent at an elevated temperature (90 °C). The synthesized Pd5@Pt5 nanodendrites showed exceptional electrochemical action toward the methanol oxidation reaction related with another compositional Pd@Pt nanodendrites and conventional Pt/C electrocatalysts. In addition, Pd5@Pt5 nanodendrites exhibited good CO tolerance owing to their surface features and the synergistic effect among Pt and Pd. Meanwhile, nanodendrites with a Pt-rich surface provided exceptional catalytic active sites. Compared with the conventional Pt/C electrocatalyst, the anodic peak current obtained by Pd5@Pt5 nanodendrites was 3.74 and 2.18 times higher in relations of mass and electrochemical active surface area-normalized current density, respectively. This approach offers an attractive strategy to design electrocatalysts with unique structures and outstanding catalytic performance and stability for electrochemical energy conversion.

Single palladium site in ordered porous heteroatom-doped carbon for high-performance alkaline hydrogen oxidation

Alkaline exchange membrane fuel cells are impeded by the lack of cost-effective, highly efficient catalysts for the sluggish hydrogen oxidation reaction (HOR). Herein, single-atomic Pd sites supported by ordered porous N,S-doped carbon are synthesized, exhibiting remarkable alkaline HOR performance. This catalyst exhibits an ultrahigh anodic current density and mass-specific kinetic current of 2.01 mA cm–2 and 27,719 A gPd–1 (at an overpotential of 50 mV), respectively, not only outperforming the Pt/C counterpart but also making it among the best reported HOR catalysts. Furthermore, this catalyst exhibits a negligible activity decay during long-term electrolysis and a good CO tolerance capability. Experiments and theoretical calculations indicate that the synergistic effect from single Pd sites and heteroatom doping (N and S) weakens the binding energy of Had intermediates, thereby accounting for its superior HOR activity. This study provides a guideline for developing single-atomic site catalysts for highly efficient, stable alkaline HOR.

DNA-Modified Cobalt Tungsten Oxide Hydroxide Hydrate Nanochains as an Effective Electrocatalyst with Amplified CO Tolerance during Methanol Oxidation.

Direct methanol fuel cell technology implementation mainly depends on the development of non-platinum catalysts with good CO tolerance. Among the widely studied transition-metal catalysts, cobalt oxide with distinctively higher catalytic efficiency is highly desirable. Here, we have evolved a simple method of synthesizing cobalt tungsten oxide hydroxide hydrate nanowires with DNA (CTOOH/DNA) and without incorporating DNA (CTOOH) by microwave irradiation and subsequently employed them as electrocatalysts for methanol oxidation. Following this, we examined the influence of incorporating DNA into CTOOH by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The enhanced electrochemical surface area of CTOOH offered readily available electroactive sites and resulted in a higher oxidation current at a lower onset potential for methanol oxidation. On the other hand, CTOOH/DNA exhibited improved CO tolerance and it was evident from the chronoamperometric studies. Herein, we noticed only a 2.5 and 1.8% drop at CTOOH- and CTOOH/DNA-modified electrodes, respectively, after 30 min. Overall, from the results, it was evident that the presence of DNA in CTOOH played an important role in the rapid removal of adsorbed intermediates and regenerated active catalyst centers possibly by creating high density surface defects around the nanochains than bare CTOOH.

Template Synthesis of Ag@Fe-N-Doped Carbon Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media

With the development of fuel cells, it is critical to find suitable oxygen reduction reaction (ORR) catalyst materials to replace current commercial Pt/C catalysts. On the one hand, atomically dispersed Fe-N-C with highly active Fe-Nx centers has been proved to be one of the best ORR catalysts comparable to the Pt/C. In addition, structural effects and strong metal-carrier interactions greatly improve performance. Therefore, various templates have been used for controlling the structure of Fe-N-C catalysts. For instance, polypyrrole is widely utilized as a nitrogen-rich carbon precursor, and hollow porous Fe3O4 microspheres with polypyrrole (PPy) encapsulated on the surface were pyrolyzed to obtain Fe-N-doped double-shell hollow carbon microspheres. Also, silica balls were applied as templates to fabricate hollow Fe-N-C carbon using a nano-casting method. These hollow structural Fe-N-C materials showed efficient ORR catalytic activities. On the other hand, Ag-based catalysts are also considered as possible candidates for ORR in alkaline medium due to their comparatively low cost and good CO tolerance capability. For example, Janus nanostructured Ag@N-C synthesized by pyrolyzing core-shell Ag@PPy demonstrated comparable ORR activity to the Pt/C, which was largely attributed to the synergistic effect between Ag nanoparticles and carbonized PPy shell. Therefore, rational design of porous Fe-N-C structure with Ag nanoparticles would achieve excellent ORR electrocatalysts. Herein, Ag@Fe3O4 nanoparticles were synthesized by a solvothermal method and utilized as templates, and PPy enveloped on the template surface functioned as nitrogen and carbon sources. After pyrolysis, hollow porous Fe-N-C was decorated with Ag nanoparticles, which demonstrated excellent ORR catalytic activity and durability in alkaline medium. Therefore, this study provides a new simple method for preparing Ag@Fe-N-C hybrid catalysts.

CO tolerant Pt electrocatalysts for PEM fuel cells with enhanced stability against electrocorrosion

An optimized route for preparation of Ti0.8Mo0.2O2–C composite supports for Pt electrocatalysts with 75/25 and 25/75 oxide/carbon mass ratio was elaborated using commercial (BP: Black Pearls 2000) and functionalized (FC) carbon materials. The sol-gel-based synthesis resulted in complete Mo incorporation into the rutile-TiO2 lattice which is a prerequisite for good CO tolerance and high stability. According to the TG and XPS measurements the highest amount of oxygen-containing functional groups was obtained on the BP carbon annealed in nitrogen at 1000 °C and functionalized with HNO3 and glucose.The electrochemical stability tests for 500 polarization cycles performed on the 20 wt% Pt/Ti0.8Mo0.2O2–C catalysts revealed similarly small performance loss (8.5–11.8%) in case of all support materials. Considering the negative effect of the oxide content of the catalyst layer on the cell resistance, the catalyst with Ti0.8Mo0.2O2/C = 25/75 ratio was chosen as the most promising.

Deep eutectic solvent-assisted synthesis of highly efficient PtCu alloy nanoclusters on carbon nanotubes for methanol oxidation reaction

Deep eutectic solvents are promising in the green synthesis of advanced functional materials owing to their several distinct advantages including good solubility, wide electrochemical window, high conductivity, low cost, nontoxicity and tolerance to humidity. Herein, we report a novel green protocol to design the hybrid PtCu nanoclusters on multi-walled carbon nanotubes in deep eutectic solvents medium without adding any surface controlling agent. Subsequently, the structure, elemental composition and electrocatalytic aspects of the as-synthesized nanohybrids are characterized by transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopic features and electrochemical investigations. Typically, the synthesis medium plays a key role to control the dispersion of Pt-based nanoparticles and to enhance the electronic transfer interaction among the catalytic nanoparticles and support material. On other hand, the addition of alloyed Cu not only further decreases the crystallite size of catalytic particles but also results in the formation of cluster nanostructure with the coarse surface. Moreover, the methanol oxidation electrocatalytic activity of the as-fabricated material is clearly composition dependent, their maximum mass activity (Pt/Cu mass ratio 1:0.25) is about 2.5 times that of the carbon nanotubes-supported monometallic Pt catalyst. And it also presents the good CO-tolerance ability and evident long-term electrochemical durability. This study suggests that the synthesis strategy in deep eutectic solvents is of great importance to design and fabricate the high-performance electrocatalysts for fuel cells applications.

Effect of the Preparation Method on the Electrocatalytic Activity of Pt-Sn/Nanotubes Catalysts Used in DMFC

A series of bimetallic Pt-Sn catalysts supported on multiwalled carbon nanotubes (NT) for methanol oxidation reaction was prepared by different methods that involve ethylene glycol synthesis under reflux conditions and sodium borohydride reduction (using water or ethylene glycol as solvents) at 55°C. Pt-Sn/NT catalysts containing 20 wt% platinum with Pt:Sn atomic ratios of 5:1, 3:1 and 1:1 were prepared and their morphology and electrocatalytic activities were characterized by temperature programmed reduction, X-ray photoelectron spectroscopy, H2 chemisorption, benzene hydrogenation reaction, transmission electron microscopy, cyclic voltammetry, linear sweep voltammetry, chronoamperometry and CO stripping. The electrocatalysts performance depends strongly on the preparation method and Pt:Sn atomic ratios, with the Pt3Sn1/NT sample prepared by ethylene glycol displaying the highest activity for methanol electrooxidation, a good CO tolerance and an important stability.

Highly Efficient Oxygen Reduction Electrocatalyst Derived from a New Three-Dimensional PolyPorphyrin

Metal-encapsulated nitrogen-doping porous carbonaceous materials (NDPCs) prepared from metalloporphyrin-based covalent organic frameworks (MP-COFs) have become very promising candidates for highly effective oxygen reduction electrocatalysts. To enhance the ORR performance and durability of these NDPCs in novel energy conversion and storage devices, we develop a new type of metal-encapsulated NDPCs (HBY-COF-900) composed of FeN4 active sites by introduction of metalloporphyrin into porous COFs. Comparable to the benchmark 20% Pt/C, HBY-COF-900 in acidic solutions exhibits higher oxygen reduction electrocatalytic activity, long-term durability, and good CO tolerance. These properties can be attributed to a synergistic effect of FeN4 active sites, high graphitization, and porous structure. This work opens an avenue for the development of metal-encapsulated NDPCs from three-dimensional polyporphyrin prepared by one-step polymerization.

Enhanced electrocatalytic activity of nitrogen-doped olympicene/graphene hybrids for the oxygen reduction reaction.

Developing inexpensive and non-precious metal electrocatalysts for the oxygen reduction reaction (ORR) is among the major goals in fuel cells. Herein, by using density-functional theory calculations, we show that N-doped olympicene/graphene hybrids exhibit unexpectedly high ORR catalytic activity-even comparable to that of the Pt(111) surface. Both graphitic-type and pyridine-type N-doped olympicene/graphene hybrids are highly active for the ORR and have good CO tolerance. The formation of the second H2O molecule is the rate-determining step for the ORR with the graphitic-type hybrid, whereas on the pyridine-type hybrid, it is the formation of OOH. Note that N-doped olympicene/graphene hybrid materials combine the high reactivity of olympicene and the high electrical conductivity of graphene, which allows them to be potentially used as low-cost and non-precious-metal ORR catalysts.

Alloyed Pt–Ru Nanoparticles Immobilized on Mesostructured Nitrogen-Doped Carbon Nanocages for Efficient Methanol Electrooxidation

Direct methanol fuel cells (DMFC) have attracted extensive attention as ideal candidates for automotive and portable applications owing to the fascinating advantages such as high conversion efficiency, environmental friendliness, safety, wide sources of methanol, and simple cell structure. Electrocatalysts are one of crucial factors limiting the performance of DMFC. Nowadays, precious Pt-based catalyst, in spite of costliness and scarcity, is the most popular catalyst for methanol oxidation reaction (MOR) at anode due to the much better performances than those of the non-Pt catalysts. But there exists some shortcomings such as poor CO-tolerance and durability. Pt alloying with other metals, e.g. Ru, is an effective strategy to improve the catalytic performance. In addition, the support with a large specific surface area (SSA), high conductivity and suitable porous structure, such as sp carbon, could lead to high dispersion, high utilization and stability of Pt-based nanoparticles, also favorable for MOR. Recently, by in situ MgO template method, we reported the unique 3D hierarchical carbon-based nanocages featured with ultrahigh SSA, micro-meso-macro-pore coexistence, good conductivity and easy doping, which exhibited excellent electrochemical performances. Herein, taking the advantages of nitrogen-dopant anchoring function and unique mesostructures of hierarchical N-doped carbon nanocages (hNCNC), we report the Pt-Ru electrocatalysts immobilized on hNCNC (Pt-Ru/hNCNC) prepared via modified microwave-assisted ethylene glycol (EG) reduction method. The so-constructed Pt-Ru/hNCNC catalysts with ca. 30 wt% loading and tunable atomic ratio of Pt to Ru have a highly homogeneous dispersion of metal nanoparticles with the average size of ca. 3 nm. The alloying Pt-Ru/hNCNC catalysts demonstrate good CO-tolerance, high MOR activity and durability, superior to those of the counterparts of Pt/hNCNC and commercial PtRu/C. The good electrochemical performance can be ascribed to the synergistic effects of the bifunctional effect due to introduction of Ru, small size and high dispersion of metal nanoparticles induced by the large SSA and nitrogen participation of hNCNC, and multi-scaled hierarchical pore structures beneficial to the mass transportation. These results proposed a potential strategy to develop the high-performance Pt-based MOR catalysts based on the novel mesostructured hNCNC.

Small‐Sized Tungsten Nitride Particles Strongly Anchored on Carbon Nanotubes and their Use as Supports for Pt for Methanol Electro‐oxidation

The anchoring of small-sized WN (tungsten nitride) nanoparticles (NPs) with good dispersion on carbon nanotubes (CNTs) offers an effective means of obtaining promising materials for use in electrocatalysis. Herein, an effective method based on grinding treatment followed by a nitridation process is proposed to realize this goal. In the synthesis, a solution containing H4 [SiO4 (W3 O9 )4 ] (SiW12 ) and CNTs modified with polyethylenimine (PEI-CNTs) was ground to dryness. Small-sized WN NPs were anchored onto the CNTs with good dispersion after calcination under NH3 . Under hydrothermal assembly conditions (absence of grinding), WN particles of larger size and with inferior dispersion were obtained, demonstrating the important role of the grinding process. The benefit of the small-sized WN has been demonstrated by using WN/CNTs as a support for Pt to catalyze the methanol electro-oxidation reaction. The mass activity of Pt-WN/CNTs-G-70 (where G denotes the grinding treatment, and 70 is the loading amount (%) of WN in the WN/CNTs) was evaluated as about 817 mA mg(-1) Pt , better that those of commercial Pt/C (340 mA mg(-1) Pt ) and Pt/CNTs (162 mA mg(-1) Pt ). The Pt-WN/CNTs-G also displayed good CO tolerance. In contrast, Pt-WN/CNTs prepared without the grinding process displayed an activity of 344 mA mg(-1) Pt , verifying the key role of grinding treatment in the preparation of WN/CNTs with good co-catalytic effect.

Activity and Stability of Molybdenum-Containing Dispersed Pt Catalysts for CO Tolerance in Proton Exchange Membrane Fuel Cell Anodes

Previous work conducted on carbon supported bimetallic (Pt-M/C, where M = Sn, Fe, Co, W or Mo, etc) catalysts have demonstrated the considerable CO tolerance of these materials when reformate hydrogen gas is used to feed the proton exchange membrane fuel cell (PEMFC) anodes. Among these bimetallic electrocatalysts, Pt-Mo composites have shown the most promising CO tolerance. This includes carbon supported Pt-Mo nanoparticles and various Pt electrodes whose surface was modified either with Mo oxides or some other Mo species. While a good CO tolerance of the anode electrocatalysts is a key challenge in the low temperature fuel cell technology, a high level of catalyst stability is also required to tolerate dynamic operating conditions involved in practical applications. Studies have shown that carbon supported Pt-Mo electrocatalysts present a CO tolerance up to threefold the tolerance of the state-of-the-art Pt-Ru/C catalysts, but their long term stability regarding the CO poisoning is under open discussion. This work reviews attempts to improve the activity and stability of Mo-containing dispersed Pt catalysts for CO tolerance in PEMFC anodes, made by using the following approaches: (1) application of a heat treatment at various temperatures ranging from 400 to 700 °C on carbon supported Pt-Mo (60:40, Pt:Mo) electrocatalyst; (2) deposition of Pt and Pt-Mo nanoparticles on carbon-supported molybdenum carbides and oxides (Mo2C/C, MoOx/C) prepared by different methods, and; (3) employing ternary and quaternary materials formed by Pt-Mo-Fe/C, Pt-Mo-Ru/C and Pt-Mo-Ru-Fe/C. Depositions of the metallic particles on the different substrates were made by a formic acid reduction process. Catalyst samples were characterized by temperature programmed reduction (TPR), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM) and wavelength dispersive X-ray spectroscopy (WDS). Electrochemical characterizations were carried out by single cell polarization measurements, CO stripping, cyclic voltammetry (CV), and online mass spectrometry (OLMS). CV and OLMS experiments have been performed to evaluate the stability and CO tolerance of the electrocatalysts. The Pt-Mo/C catalyst treated at 600 °C, for which the average crystallite size was 16.7 nm, showed a better stability up to 5000 potential cycles of cyclic voltammetry and a higher hydrogen oxidation activity in the presence of CO, compared to untreated Pt-Mo/C, giving an overpotential induced by CO contamination of 100 mV at 1 Acm-2. Similar observations were made for the PtMoRuFe/C, PtMoFe/C and PtMoRu/C electrocatalysts. In the cases of Pt and Pt-Mo supported on Mo2C/C, and also for PtMoRuFe/C, PtMoFe/C and PtMoRu/C the results also evidenced a better stability than Pt-Mo supported on carbon. In all cases, a partial dissolution of Mo from the anode and its migration toward cathode during the cell operation was observed. This was also seen for Ru and Fe, in the cases of ternary and quaternary materials. On the basis of polarization measurements and cyclic voltammograms, it is concluded that the stability of anode electrocatalysts can be improved either by heat treatment of Pt-Mo/C, or by using molybdenum carbide as catalyst support or even by using Mo-containing ternary and quaternary electrocatalysts. Acknowledgments: This work has been supported by Fundação de Amparo a Pesquisa do Estado de São Paulo and Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil.

Synthesis of boron doped graphene for oxygen reduction reaction in fuel cells

Boron atoms, with strong electron-withdrawing capability, are doped into graphene frameworks forming boron doped graphene (BG) via a catalyst-free thermal annealing approach in the presence of boron oxide. Atomic force microscopic (AFM) and transmission electron microscopic (TEM) characterizations reveal that the as-prepared BG has a flake-like structure with an average thickness of ca. 2 nm. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that boron atoms can be successfully doped into graphene structures with the atomic percentage of 3.2%. Due to its particular structure and unique electronic properties, the resultant BG exhibits excellent electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline electrolytes, similar to the performance of Pt catalysts. In addition, the non-metallic BG catalyst shows long-term stability and good CO tolerance superior to that of Pt-based catalysts. These results demonstrate that the BG, as a promising candidate in advanced electrode materials, may substitute Pt-based nanomaterials as a cathode catalyst for ORR in fuel cells as well as other electrochemical applications similar to the reported nitrogen doped graphene.

A Promising Approach to the Synthesis of 3D Nanoporous Graphitic Carbon as a Unique Electrocatalyst Support for Methanol Oxidation

A 3D nanoporous graphitic carbon (g-C) material is synthesized by using an adamantane (C(10)H(16)) flame, and utilized to support a Pt(50)-Ru(50) alloy catalyst. The physico-chemical properties of the Pt(50)-Ru(50)/3D nanoporous g-C electrode are examined by a range of spectroscopy techniques as well as Brunauer-Emmett-Teller surface area analysis. Cyclic voltammetry measurements are used for electrochemical characterization of the Pt(50)-Ru(50)/3D nanoporous g-C electrode. The electrochemical investigations show that the supported Pt(50)-Ru(50) has excellent activity and stability towards methanol electro-oxidation. Good CO tolerance is also shown, and considered to be due to the presence of Ru nanoparticles. It is proposed that Ru is able to promote the oxidation of strongly adsorbed CO on Pt by supplying an oxygen source: Ru(OH)(ad). Moreover, the presence of 3D nanopores in the g-C support may also contribute to the observed higher current density by virtue of the easy transport of methanol and the oxidation products through these nanopores.

Platinum particles supported on titanium nitride: an efficient electrode material for the oxidation of methanol in alkaline media

In the present study, titanium nitride which shows exceptional stability, extreme corrosion resistance, good electronic conductivity and adhesion behaviour is used to support platinum particles and then used for methanol oxidation in an alkaline medium. The catalyst shows very good CO tolerance for the electrochemical oxidation of methanol. In situ infrared spectroelectrochemical data show the remarkable ability of TiN to decompose water at low over potentials leading to –OH type functional groups on its surface which in turn help in alleviating the carbon monoxide poisoning associated with methanol oxidation. TiN supported catalysts are found to be very good in terms of long term stability, exchange current density and stable currents at low over voltages. Supporting evidence from X-ray photoelectron spectroscopic data and cyclic voltammetry clearly demonstrates the usefulness of TiN supported Pt catalysts for efficient methanol oxidation in alkaline media.

Ordered silicon nanocones as a highly efficient platinum catalyst support for direct methanol fuel cells

Platinum nanoparticles were electrodeposited on ordered silicon nanocones (SNCs) and used as the catalyst for methanol electro-oxidation in direct methanol fuel cells (DMFCs). Because of uniform dispersion of Pt nanoparticles and the high surface area, the Pt-SNC electrode exhibited superior electrocatalytic properties toward the methanol electro-oxidation, with the onset potential of 0.08 V (vs. SCE). According to chronoamperometric analysis and CO stripping cyclic voltammetric (CV) study, the Pt/SNC electrode had a stable electro-oxidation activity with a very good CO tolerance. The Si surface oxide surrounding the Pt nanoparticles on the SNCs was suggested to play a key role in improving the CO tolerance via the bifunctional mechanism.

熱拡散白金ルテニウム合金触媒の組成比が耐一酸化炭素被毒特性へ与える影響

Platinum-ruthenium catalysts of various Pt:Ru ratios were prepared by a newly developed three-step method for use as anodes in stationary polymer electrolyte fuel cells. As the first step, a well-dispersed platinum catalyst was prepared, and then ruthenium was deposited in the vicinity of the platinum particles by a chemical deposition method as the second step. As the final step, the Pt–Ru catalysts were heat-treated to obtain well-alloyed structures. The Pt–Ru catalysts prepared by this method showed good CO tolerance, even though the particle size was relatively large. The CO tolerance increased with increasing the ruthenium content, and the highest CO tolerance was obtained at Pt:Ru ratios in the range of 1:2 to 1:3. On air bleeding, the catalysts of a wider range of Pt:Ru ratios showed good CO tolerance. Potential sweep durability tests revealed that the stability of the Pt–Ru catalysts of Pt:Ru=1:1 against high potentials (1000 mV vs. RHE) was lower than that of the catalysts of Pt:Ru=1:1.5 and 1:2.

Influência de M/C (M = Mo, Cu, Fe e W) incorporado à camada difusora do eletrodo de difusão de gás frente à reação de oxidação de hidrogênio na presença de CO

The performance of proton exchange membrane fuel cells (PEMFC) with Pt-based anodes is drastically lowered when CO-containing hydrogen is used to feed the system, because of the strong adsorption of CO on platinum. In the present work the effects of the presence of a conversion layer of CO to CO2 composed by several M/C materials (where M = Mo, Cu, Fe and W) in gas diffusion anodes formed by Pt catalysts were investigated. The diffusion layers formed by Mo/C e W/C show good CO-tolerance, and this was attributed to the CO removal by parallel occurrence of the water-gas shift reaction and the so-called bifunctional mechanism.