Enhanced Methanol Tolerance Research Articles

Porous AgPd Nanomushrooms with Enhanced Methanol Tolerance for Oxygen Reduction Reaction

Porous AgPd Nanomushrooms with Enhanced Methanol Tolerance for Oxygen Reduction Reaction

Dual Single-Atomic Co-Mn Sites in Metal-Organic-Framework-Derived N-Doped Nanoporous Carbon for Electrochemical Oxygen Reduction.

Synthesizing dual single-atom catalysts (DSACs) with atomically isolated metal pairs is a challenging task but can be an effective way to enhance the performance for electrochemical oxygen reduction reaction (ORR). Herein, well-defined DSACs of Co-Mn, stabilized in N-doped porous carbon polyhedra (named CoMn/NC), are synthesized using high-temperature pyrolysis of a Co/Mn-doped zeolitic imidazolate framework. The atomically isolated Co-Mn site in CoMn/NC is recognized by combining microscopic as well as spectroscopic techniques. CoMn/NC exhibited excellent ORR activities in alkaline (E1/2 = 0.89 V) as well as in acidic (E1/2 = 0.82 V) electrolytes with long-term durability and enhanced methanol tolerance. Density functional theory (DFT) suggests that the Co-Mn site is efficiently activating the O-O bond via bridging adsorption, decisive for the 4e- oxygen reduction process. Though the Co-Mn sites favor O2 activation via the dissociative ORR mechanism, stronger adsorption of the intermediates in the dissociative path degrades the overall ORR activity. Our DFT studies conclude that the ORR on an Co-Mn site mainly occurs via bridging side-on O2 adsorption following thermodynamically and kinetically favorable associative mechanistic pathways with a lower overpotential and activation barrier. CoMn/NC performed excellently as a cathode in a proton exchange membrane (PEM) fuel cell and rechargeable Zn-air battery with high peak power densities of 970 and 176 mW cm-2, respectively. This work provides the guidelines for the rational design and synthesis of nonprecious DSACs for enhancing the ORR activity as well as the robustness of DSACs and suggests a design of multifunctional robust electrocatalysts for energy storage and conversion devices.

Bimetallic palladium-copper nanoplates with optimized d-band center simultaneously boost oxygen reduction activity and methanol tolerance.

The methanol-poisoning of electrocatalysts at the cathodic part of direct methanol fuel cells (DMFCs) can severely degrade the overall efficiency. Therefore, engineering cathodic catalysts with outstanding oxygen reduction activity, and simultaneously, superior methanol tolerance is greatly desired. Herein, bimetallic palladium-copper (PdCu) nanoplates with the optimized d-band center are designed as promising cathodic catalysts for DMFCs. It shows outstanding oxygen reduction activity with a mass activity (MA) of 0.522AmgPd-1 in alkaline electrolyte, overwhelming the benchmarked commercial Pt/C and Pd/C. Meanwhile, it has prominent stability with only 4.0 % loss in MA after continuous 20K cycles. More importantly, the PdCu nanoplates are almost inert toward methanol oxidation and show excellent anti-methanol capability. The theoretical calculations reveal that the downshift of d-band center in PdCu nanoplates and the electronic interaction between Pd and Cu atoms could effectively lower the methanol adsorption energy, thus leading to enhanced methanol tolerance. This work highlights the important role of tuning the electronic structure and optimized geometry of electrocatalysts to simultaneously boost their oxygen reduction activity, stability, and methanol tolerance for their future application in DMFCs.

Au@Ir core-shell nanowires towards oxygen reduction reaction

• Preparation of Au@Ir core-shell nanowires (Au@Ir CSNWs). • Au@Ir CSNWs have high aspect ratio and ultrathin Ir shell thickness. • Au@Ir CSNWs show super electrocatalytic activity towards ORR activity. • Au@Ir CSNWs display excellent methanol tolerance and durability towards ORR. Noble metal based one-dimensionally (1D) bimetallic nanostructures are attracting increasing interest in energy conversion field because of their structural advantages and tunable chemical composition. At present, the facile and efficient synthesis of high-quality Au-core noble metal-shell nanowires still maintains the challenge. Herein, we develop a feasible one-pot chemical-reduction strategy to rapidly synthesize high-quality Au@Ir core–shell nanowires (Au@Ir CSNWs) in 1-naphthol ethanol solution and explore their potential application in electrocatalysis. Expermattial results show the formation core–shell structure originates from the deposition-growth of Ir atoms at preferentially generated Au nanowires surface. When using as an electrocatalyst towards oxygen reduction reaction (ORR) in alkaline media, Au@Ir CSNWs show Pt-like ORR electroactivity due to the compositional synergism effect and structural advantages of 1D nanowires, accompanying with excellent durability and extremely enhanced methanol tolerance towards ORR.

Pyrolysis-Derived Carbon Auto-Coated Co–Ni Oxide-based Nanoparticles on Graphene-like Nanosheets for High-Performance Oxygen Electrocatalysis

Engineering transition-metal-based bifunctional oxygen electrocatalysts with high activity and stability has always been a problem. Traditional bare transition-metal-based nanoparticles supported on the outer surface of carbon materials are susceptible to the Ostwald-ripening effect in a catalytic process, consequently suffering from poor long-term operation. However, constructing a highly efficient and stable bifunctional oxygen electrocatalyst is still challenging. Here, we report graphene-like carbon nanosheets modified with carbon shell-coated binary Co–Ni oxide-based nanoparticles (CoNiOx@C/G-NSs) by one-step pyrolysis method, in which the hybrids show a three-dimensional fluffy and hierarchical porous nanostructure and large numbers of carbon shell-coated binary Co–Ni oxide-based nanoparticles (CoNiOx@C) dispersed on graphene-like carbon nanosheets evenly. More excitingly, the carbon nanosheets are nitrogen-doped. When applied for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), the onset potential (Eonset) of OER reached 1.26 V, and onset potential of ORR and half-wave potential (E1/2) reached 0.90 and 0.78 V, respectively. The hybrids showed enhanced methanol tolerance, with few changes in the ORR performance with or without adding methanol, and high stability, with 84% activity retention after 10 h continuous reaction. The productivity of H2O2 is about 5% and the number of electron transfer (n) is about 3.9 in the process of catalyzing ORR; density functional theory calculation reveals its high selectivity in the 4e– pathway. Its excellent performance is mainly attributed to the synergistic enhancement effect: three-dimensional fluffy and hierarchical porous nanostructure provided a large catalytic activity area, which enabled the effective participation of species and facilitated rapid mass transfer; the rapid adsorption of O2 by N-doped graphene-like carbon nanosheets ensured fast electron transport; synergistic reactivity between carbon shell and CoNiOx enhanced the activity, and numerous CoNiOx@C nanoparticles reconciled the electron density of the carbon shell, which introduced more active sites; and the carbon shell weakened the Ostwald-ripening effect and ensured the stability of the nanoparticle. All advantages synergistically enhance the catalytic efficiency and make it one of the best bifunctional oxygen electrocatalysts.

Engineering of Coordination Environment and Multiscale Structure in Single-Site Copper Catalyst for Superior Electrocatalytic Oxygen Reduction.

Herein, we report efficient single copper atom catalysts that consist of dense atomic Cu sites dispersed on a three-dimensional carbon matrix with highly enhanced mesoporous structures and improved active site accessibility (Cu-SA/NC(meso)). The ratio of +1 to +2 oxidation state of the Cu sites in the Cu-SA/NC(meso) catalysts can be controlled by varying the urea content in the adsorption precursor, and the activity for ORR increases with the addition of Cu1+ sites. The optimal Cu1+-SA/NC(meso)-7 catalyst with highly accessible Cu1+ sites exhibits superior ORR activity in alkaline media with a half-wave potential (E1/2) of 0.898 V vs RHE, significantly exceeding the commercial Pt/C, along with high durability and enhanced methanol tolerance. Control experiments and theoretical calculations demonstrate that the superior ORR catalytic performance of Cu1+-SA/NC(meso)-7 catalyst is attributed to the atomically dispersed Cu1+ sites in catalyzing the reaction and the advantage of the introduced mesoporous structure in enhancing the mass transport.

Synergistic heat treatment derived hollow-mesoporous-microporous Fe–N–C-SHT electrocatalyst for oxygen reduction reaction

Abstract Exploring an economical and efficient oxygen reduction reaction (ORR) is an essential but challenging field of study. Metal–organic frameworks (MOFs) have emerged as promising candidates for the preparation of porous catalysts. Here we propose a synergistic heat treatment (SHT) method to synthesize Fe–N–C-SHT catalyst with hierarchical porous hollow structures via a simple carbonization method by the synergistic heating of ZIF-8-Fe (ZIF-8 doped with Fe) and ZIF-67 in a tube furnace. Fe–N–C-SHT catalyst displays efficient ORR activity (half-wave potential (Ehalf) = 0.88 V versus reversible hydrogen electrode (RHE) with a loading of 0.204 mgFe-N-C-SHTcm−2), which is superior to that of Fe–N–C synthesized using individual heat treatment (IHT) (Ehalf = 0.84 V) and Pt/C catalyst (Ehalf = 0.86 V). We achieve enhanced catalytic properties, enhanced methanol tolerance, and long-term durability of the Fe–N–C-SHT catalyst in alkaline electrolyte. The improved ORR activity is attributed to the synergistic effect of Fe doping and optimized SHT methodology, which led to the formation of a highly porous catalyst with numerous active sites. The developed SHT method presents a novel route to fabricate Fe–N–C catalysts with hollow-mesoporous-microporous structures and high performance in ORR.

Development of g-C3N4 activated hollow carbon spheres with good performance for oxygen reduction and selective capture of acid gases

A variety of nitrogen-doped hollow carbon nanospheres (A–NHCN–Ts, where T stands for activation temperature) with abundant microporosity were developed by us in this work. The A–NHCN–Ts were synthesized from carbonization of silica-resorcinol formaldehyde core-shell composites (silica@RF). The resulting silica@carbon core-shell composites were then treated with KOH to enrich microporosity, fast activation with g-C3N4 to improve nitrogen-doping, and etched with HF to removal silica core. The silica@RF was synthesized from coating of silica nanosphere with resorcinol-formaldehyde resin in presence of hexamethylenetetramine crosslinker. A–NHCN–Ts exhibit hollow and uniform sphericity, large BET surface areas (704–1043 m2/g) and hierarchical porosity. Abundant nitrogen sites (11.6–14.8 wt%) with high percentages of pyridinic-N (55–70%) were doped in A–NHCN–Ts. As a result, A–NHCN–Ts can be used as high-efficient and long-lived electrocatalysts in oxygen reduction reaction (ORR). The reduction potential of A–NHCN–Ts activated at 800 °C (A–NHCN–800) is 0.8 V versus reversible hydrogen electrode (vs. RHE) in alkaline electrolyte, with a half-wave potential of 0.81 V (vs. RHE), an onset potential of 0.9 V (vs. RHE) and a limiting current density of 3.63 mA cm−2 at a rotation of 1600 rpm, respectively. A–NHCN–800 exhibits comparable ORR activity, enhanced methanol tolerance and superb stability in comparison with commercial Pt/C (20%). A–NHCN–Ts also show competitive properties in the capture of acid gases of SO2 and CO2, and the CO2 can be mildly catalyzed into cyclic carbonates over metalized A–NHCN–Ts. This work provides a novel g-C3N4 fast activation strategy for designing of high-efficient, multiple functional nanocarbon materials in both ORR, acid gases selective capture and conversion.

One-Pot Synthesis of NiCo2S4 Hollow Spheres via Sequential Ion-Exchange as an Enhanced Oxygen Bifunctional Electrocatalyst in Alkaline Solution.

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are considered to be cornerstones of many energy conversion and storage technologies. It is difficult studying high-performance nonprecious materials as cost-effective bifunctional electrocatalysts for both the OER and ORR in future practical applications. In this study, NiCo2S4 hollow spheres (NiCo2S4 HSs) were fabricated via an effective and facile one-pot "green" approach in an N, N-dimethylformamide-ethylene glycol binary solution. The obtained NiCo2S4 HSs had a high specific surface area as well as numerous active sites and showed a remarkable catalytic performance and durability toward both the OER and ORR in an alkaline electrolyte. For the ORR, NiCo2S4 HSs exhibited a positive half-wave potential of 0.80 V and demonstrated outstanding stability and enhanced methanol tolerance. For the OER, NiCo2S4 HSs presented a low overpotential (400 mV) at a current density of 10 mA cm-2, small Tafel slope, and excellent stability in 0.1 M KOH. Moreover, regarding the overall electrocatalytic activity, the potential difference of NiCo2S4 HSs was 0.83 V, surpassing that of NiCo2S4 nanoparticles, binary counterparts (CoS, NiS), and most highly active bifunctional catalysts described in the literature. The superior catalytic performance of NiCo2S4 HSs is mainly ascribed to its unique hollow structure, which increases molecular diffusion and adsorption, as well as the synergistic effect of Ni and Co, which offers richer redox reaction sites. Importantly, this strategy may facilitate the design and preparation of excellent bifunctional nonprecious metal electrocatalysts in various domains.

Nano-Porous Electro-Catalyst with Textured Surface Active Pd-Pt Islands for Efficient Methanol Tolerant Oxygen Reduction Reaction

Herein, we report a simple and elegant aqueous synthesis of Pd100-xPtx (x=5, 10, 15 and 20) nano-porous structures (NPoS) derived from Pd100-xMn2x (x=5, 10, 15 and 20) nano-alloys. Pd100-xPtx/C NPoS exhibit enhanced oxygen reduction reaction (ORR) activity along with higher retention of figure of merit in the presence of methanol compared to HiSPEC Pt/C catalyst. The ORR mass and specific activity values of Pd100-xPtx/C NPoS are high and exceed the U.S. department of energy (DOE) 2017–2020 targets. The enhanced methanol tolerance and ORR activity of Pd100-xPtx/C NPoS is attributed to their unique surface active Pd−Pt islands on nano-porous Pd. Direct methanol fuel cell performance studies employed using Pd85Pt15/C NPoS as cathode material (0.4 mgPt/cm2) and HiSPEC PtRu/C NPs as anode material (0.2 mgPt/cm2) shows improved direct methanol fuel cell (DMFC) single cell activity at low Pt loading and the results are presented.

An advanced electrocatalyst of Pt decorated SnO2/C nanofibers for oxygen reduction reaction

In this report, an efficient oxygen reduction reaction (ORR) electrocatalyst of platinum (Pt) decorated SnO2/C (Pt/SnO2/C) nanofiber was fabricated by using a Pt galvanic displacement of a copper (Cu) layer electrodeposited on electrospinning SnO2/C nanofiber. Microscopic and spectroscopic characterizations revealed that the facile electrospinning and galvanic displacement route generated numerous dispersed Pt nanoparticles on the SnO2/C nanofiber; and Pt nanoparticles (d ~2–3nm) with high composition of Pt (111) facet were preferably deposited at the SnO2/C junctions to form triple junction nanostructures. The resulting Pt/SnO2/C nanocomposite presented an onset potential of 0.02V vs RHE, specific activity of 1.12mAcm−2 and mass activity of 615mA/mgPt at −0.05V vs RHE. It is competitive to commercial Pt/C (10wt% Pt) catalyst toward ORR. Notably, in comparison with commercial Pt/C, the composition displayed superior electrochemical durability and enhanced methanol tolerance. It was demonstrated that the presence of Pt/SnO2/C triple junction nanostructures coupled with high composition of Pt (111) facets synergistically contributed the enhanced ORR activity, while the good conductivity of the C facilitates the electron transfer during the ORR process. The metal-metal oxide-carbonaceous heterogeneous structure represents a promising platform for designing ORR catalysts with high performance.

Synthesis, characterization, and electrochemical performance of nitrogen-modified Pt–Fe alloy nanoparticles supported on ordered mesoporous carbons

A method has been demonstrated to synthesize nitrogen-modified Pt–Fe alloyed nanoparticles (9.2–11.3 nm) supported on ordered mesoporous carbon (Pt x Fe100−x N/OMC), which is fabricated by a conventional wet chemical synthesis of Pt–Fe alloyed nanoparticles and followed by carbonization of the nanoparticles with tetraethylenepentamine as nitrogen chelating agent. Among these electrocatalysts, the Pt30Fe70N/OMC has highly catalytic activity for the oxygen reduction reaction (ORR) with significantly enhanced methanol tolerance as well. Combining the results from X-ray diffraction and X-ray absorption spectroscopy, it can be observed that Pt metal in the Pt30Fe70N/OMC is present in the outer shell of Pt–Fe alloys with face-centered cubic crystalline structure. By X-ray photoelectron spectroscopy, the nitrogen-modified Pt surface of Pt30Fe70N/OMC exhibits significant selectivity toward the ORR in the presence of methanol. This enhancement of methanol tolerance could be attributed to the inhibition of methanol adsorption resulting from the modification of the Pt surface with nitrogen.

Identification of two mutations increasing the methanol tolerance of Corynebacterium glutamicum.

BackgroundMethanol is present in most ecosystems and may also occur in industrial applications, e.g. as an impurity of carbon sources such as technical glycerol. Methanol often inhibits growth of bacteria, thus, methanol tolerance may limit fermentative production processes.ResultsThe methanol tolerance of the amino acid producing soil bacterium Corynebacterium glutamicum was improved by experimental evolution in the presence of methanol. The resulting strain Tol1 exhibited significantly increased growth rates in the presence of up to 1 M methanol. However, neither transcriptional changes nor increased enzyme activities of the linear methanol oxidation pathway were observed, which was in accordance with the finding that tolerance to the downstream metabolites formaldehyde and formate was not improved. Genome sequence analysis of strain Tol1 revealed two point mutations potentially relevant to enhanced methanol tolerance: one leading to the amino acid exchange A165T of O-acetylhomoserine sulfhydrolase MetY and the other leading to shortened CoA transferase Cat (Q342*). Introduction of either mutation into the genome of C. glutamicum wild type increased methanol tolerance and introduction of both mutations into C. glutamicum was sufficient to achieve methanol tolerance almost indistinguishable from that of strain Tol1.ConclusionThe methanol tolerance of C. glutamicum can be increased by two point mutations leading to amino acid exchange of O-acetylhomoserine sulfhydrolase MetY and shortened CoA transferase Cat. Introduction of these mutations into producer strains may be helpful when using carbon sources containing methanol as component or impurity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0558-6) contains supplementary material, which is available to authorized users.

Enhanced Methanol Tolerance of Highly Pd rich Pd-Pt Cathode Electrocatalysts in Direct Methanol Fuel Cells

Methanol crossover critically restricts the practical application of direct methanol fuel cells (DMFCs). To resolve this crucial difficulty from the standpoint of electrocatalysis, an electrode material having high activity for the oxygen reduction reaction and low activity for the methanol oxidation reaction compared to widely used Pt-based electrodes is needed for DMFC cathodes. In this research carbon-supported Pd-rich Pd–Pt bimetallic nanoparticle electrocatalysts with 60wt.% metal content were prepared for this purpose by sodium borohydride reduction of metal chlorides. The physical features of the prepared nanoparticles were investigated by transmission electron microscopy, energy dispersive X-ray spectroscopy, atomic absorption spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption near edge spectroscopy. Methanol tolerance was tested by means of rotating disk electrode (RDE) voltammetry using oxygen-saturated methanol-containing electrolyte solutions as the anode fuel for DMFC unit cell performance tests. In the RDE measurements, Pd-rich electrocatalysts (carbon-supported Pd19Pt1 nanoparticles) showed excellent methanol tolerance compared with Pd-free Pt electrocatalyst. When Pd19Pt1 nanoparticles were used as a DMFC cathode catalyst, unit cell performance tests showed that the i-V curves of the Pd19Pt1 electrocatalyst decreased slightly with increasing methanol concentration, while that of the Pt electrocatalyst decreased rapidly. The results in a liquid-feed DMFC unit cell test were in good agreement with the methanol tolerant characteristics identified in the RDE measurements.

Biomass-derived nitrogen self-doped porous carbon as effective metal-free catalysts for oxygen reduction reaction.

Biomass-derived nitrogen self-doped porous carbon was synthesized by a facile procedure based on simple pyrolysis of water hyacinth (eichhornia crassipes) at controlled temperatures (600-800 °C) with ZnCl2 as an activation reagent. The obtained porous carbon exhibited a BET surface area up to 950.6 m(2) g(-1), and various forms of nitrogen (pyridinic, pyrrolic and graphitic) were found to be incorporated into the carbon molecular skeleton. Electrochemical measurements showed that the nitrogen self-doped carbons possessed a high electrocatalytic activity for ORR in alkaline media that was highly comparable to that of commercial 20% Pt/C catalysts. Experimentally, the best performance was identified with the sample prepared at 700 °C, with the onset potential at ca. +0.98 V vs. RHE, that possessed the highest concentrations of pyridinic and graphitic nitrogens among the series. Moreover, the porous carbon catalysts showed excellent long-term stability and much enhanced methanol tolerance, as compared to commercial Pt/C. The performance was also markedly better than or at least comparable to the leading results in the literature based on biomass-derived carbon catalysts for ORR. The results suggested a promising route based on economical and sustainable biomass towards the development and engineering of value-added carbon materials as effective metal-free cathode catalysts for alkaline fuel cells.

PtPdCo ternary electrocatalyst for methanol tolerant oxygen reduction reaction in direct methanol fuel cell

Carbon-supported PtPdCo/C ternary electrocatalysts were prepared by using the sodium borohydride method for use as a cathode catalyst in direct methanol fuel cells (DMFCs). The electrocatalyst particles with a size of 2–3nm were uniformly dispersed on carbon supports. PtPdCo/C showed a similar performance compared to commercial Pt/C in the oxygen reduction reaction (ORR) tests conducted with a rotating disk electrode (RDE). On the other hand, PtPdCo/C showed higher methanol tolerance than Pt/C in acidic media with methanol. In the single-cell tests, the performance of the PtPdCo/C electrocatalyst was approximately 50% higher than that of Pt/C owing to its enhanced methanol tolerance. In the long-term operation test with the single-cell, the maximum power density of PtPdCo/C decreased only by 14% from its initial value. These results indicate that the PtPdCo/C catalyst is potentially an alternative electrocatalyst for the cathode in DMFCs.

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).

Carbon-Supported Pt – TiO2 as a Methanol-Tolerant Oxygen-Reduction Catalyst for DMFCs

Carbon-supported catalysts with varying at. wt ratios of Pt to Ti, namely, 1:1, 2:1, and 3:1, are prepared by the sol–gel method. The electrocatalytic activity of the catalysts toward oxygen reduction reaction (ORR), both in the presence and absence of methanol, is evaluated for application in direct methanol fuel cells (DMFCs). The optimum at. wt ratio of Pt to Ti in is established by fuel cell polarization, linear sweep voltammetry, and cyclic voltammetry studies. heat-treated at with Pt and Ti in an at. wt ratio of 2:1 shows enhanced methanol tolerance, while maintaining high catalytic activity toward ORR. The DMFC with a cathode catalyst exhibits an enhanced peak power density of in contrast to the achieved from the DMFC with carbon-supported Pt catalyst while operating under identical conditions. Complementary data on the influence of on the crystallinity of Pt, surface morphology, and particle size, surface oxidation states of individual constituents, and bulk and surface compositions are also obtained by powder X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, energy dispersive analysis by X-ray, and inductively coupled plasma optical emission spectrometry.

Simple preparation of Pd–Pt nanoalloy catalysts for methanol-tolerant oxygen reduction

Carbon-supported Pd–Pt bimetallic nanoparticles of different atomic ratios (Pd–Pt/C) have been prepared by a simple procedure involving the complexing of Pd and Pt species with sodium citrate followed by ethylene glycol reduction. As-prepared Pd–Pt alloy nanoparticles evidence a single-phase fcc disordered structure, and the degree of alloying is found to increase with Pd content. Both X-ray diffraction and transmission electron microscopy characterizations indicate that all the Pd–Pt/C catalysts possess a similar mean particle size of ca. 2.8 nm. The highest mass and specific activity of the oxygen reduction reaction (ORR) using the Pd–Pt/C catalysts are found with a Pd:Pt atomic ratio of 1:2. Moreover, all Pd–Pt alloy catalysts exhibit significantly enhanced methanol tolerance during the ORR than the Pt/C catalyst, ensuring a higher ORR performance while diminishing Pt utilization.

Carbon nanotubes supported Pt–Au catalysts for methanol-tolerant oxygen reduction reaction: A comparison between Pt/Au and PtAu nanoparticles

Abstract Two kinds of Pt–Au/CNT catalysts with different structures are prepared by synthesizing the formerly separated Pt/Au (Au separating Pt) in separate solutions, and PtAu nanoparticles in mixed solution using the borohydride reduction method with trisodium citrate as the stabilizing agent, and then depositing the metal colloid nanoparticles on the carbon nanotubes supporting material. The structural information and particle size are characterized by UV–vis absorption spectra, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results confirm the formation of Pt–Au nanoparticles with PtAu and separated Pt/Au structures. The catalytic activities for methanol oxidation reaction and oxygen reduction reaction are examined by electrochemical measurements. Compared with the Pt/CNT catalyst, the two Pt–Au/CNT catalysts show a lower overpotential for the oxygen reduction reaction in the presence of methanol, indicating a higher methanol tolerance on Au-modified Pt nanoparticles. Particularly, the Pt/Au/CNT catalyst with Au separating Pt nanoparticles structure exhibits the significantly higher methanol tolerance than PtAu/CNT catalyst. The enhanced methanol tolerance may be attributed to less methanol adsorption on Pt surface due to the effect of Au nanoparticles.