Relating structural aspects of bimetallic Pt(3)Cr(1)/C nanoparticles to their electrocatalytic activity, stability, and selectivity in the oxygen reduction reaction

Two methods were used to prepare bimetallic Pt(3)Cr(1)/C nanocatalysts with similar composition but different alloying extent (structure). We investigated how these differences in alloying extent affect the catalytic activity, stability and selectivity in the oxygen reduction reaction (ORR). One method, based on slow thermal decomposition of the Cr precursor at a rate that matches that of chemical reduction of the Pt precursor, allows fine control of the composition of the Pt(3)Cr(1)/C alloy, whereas the second approach, using the ethylene glycol method, results in considerable deviation (>25 %) from the projected composition. Consequently, these two methods lead to variations in the alloying extent that strongly influence the Pt d-band vacancy and the Pt electroactive surface area (Pt ESCA). This relationship was systematically evaluated by transmission electron microscopy, X-ray absorption near edge structure spectroscopy, and electrochemical analysis. The ORR activity depends on two effects that nullify each other, namely, the number of active Pt sites and their activity. The Pt-site activity is more dominant in governing the ORR activity. The selectivity of the nanocatalyst towards the ORR and the competitive methanol oxidation reaction (MOR) depend on these two effects acting in cooperation to give enhanced ORR activity with suppressed MOR. The number of active Pt sites is associated with the Pt ESCA value, while Pt-site activity is associated with the alloying extent and Pt d-band vacancy (electronic) effects. The presence of Cr atoms in Pt(3)Cr(1)/C enhances stability during electrochemical treatment. Overall, the Pt(3)Cr(1)/C catalyst prepared by controlled-composition synthesis was shown to be superior in ORR activity, selectivity and stability owing to its favorable alloying extent, Pt d-band vacancy, and Pt ESCA.     

Au nanowires with high aspect ratio and atomic shell of Pt-Ru alloy for enhanced methanol oxidation reaction

The methanol oxidation reaction(MOR) is the limiting half-reaction in direct methanol fuel cell(DMFC).Although Pt is the most active single-metal electrocatalyst for MOR,it is hampered by high cost and CO poisoning.Constructing a Pt or Ru monolayer on a second metal substrate by means of galvanic replacement of underpotentially deposited(UPD) Cu monolayer has been shown as an efficient catalyst design strategy for the electrocatalysis of MOR because of the presumed 100% utilization of atoms and resistance to CO poisoning.Herein,we prepared one-dimensional surface-alloyed electrocatalyst from predominantly(111) faceted Au nanowires with high aspect ratio as the substrate of under-potential deposition.The electrocatalyst comprises a core of the Au nanowire and a shell of catalytically active Pt coated by Ru.Coverage-dependent electro-catalytic activity and stability is demonstrated on the Pt/Ru submonolayers on Au wires for MOR.Among all these catalysts,Au@Pt_(ML)@Ru_(ML) exhibits the best electrocatalytic activity and poisoning tolerance to CO.This presents a viable method for the rational catalyst design for achieving high noble-metal utilization efficiency and high catalytic performance.     

石墨烯衍生物负载的纳米催化剂用于氧还原反应

综述了用于燃料电池中氧还原反应(ORR)的石墨烯衍生物负载的各种纳米催化剂的最新进展。介绍了用于表征石墨烯基电催化剂的常规电化学技术以及石墨烯基电催化剂最新的研究进展。负载于还原氧化石墨烯(RGO)上的Pt催化剂的电化学活性和稳定性均得到显著提高。其它贵金属催化剂,如Pd, Au和Ag也表现出较高的催化活性。当以RGO或少层石墨烯为载体时, Pd催化剂的稳定性提高。讨论了氧化石墨烯负载Au或Ag催化剂的合成方法。另外,以N4螯合络合物形式存在的非贵过渡金属可降低氧的电化学性能。 Fe和Co是可替代的廉价ORR催化剂。在大多数情况下,这些催化剂稳定性和耐受性的问题均可得到解决,但其整体性能还很难超越Pt/C催化剂。     

Characterization of carbon-supported AuPt nanoparticles for electrocatalytic methanol oxidation reaction

In view of the recent finding that the bimetallic AuPt nanoparticles prepared by molecular-capping-based colloidal synthesis and subsequent assembly on carbon black support and thermal activation treatment exhibit alloy properties, which is in sharp contrast to the bimetallic miscibility gap known for the bulk counterparts in a wide composition range, there is a clear need to assess the electrocatalytic properties of the catalysts prepared with different bimetallic composition and different thermal treatment temperatures. This paper reports recent results of such an investigation of the electrocatalytic methanol oxidation reaction (MOR) activities of the carbon-supported AuPt nanoparticle catalysts with different bimetallic composition and thermal treatment temperatures. Au(m)Pt(100)(-)(m) nanoparticles of 2-3 nm core sizes with different atomic compositions ranging from 10% to 90% Au (m = 10 approximately 90) have been synthesized by controlling the feeding of the metal precursors used in the synthesis. The electrocatalytic MOR activities of the carbon-supported AuPt bimetallic catalysts were characterized in alkaline electrolytes. The catalysts with 65% to 85% Au and treated at 500 degrees C were found to exhibit maximum electrocatalytic activities in the alkaline electrolytes. The findings, together with a comparison with some well-documented catalysts as well as recent experimental and theoretical modeling results, have revealed important insights into the participation of CO(ad) and OH(ad) on Au sites in the catalytic reaction of Pt in the AuPt alloys with approximately 75% Au. The insights are useful for understanding the correlation of the bifunctional electrocatalytic activity of the bimetallic nanoparticle catalysts with the bimetallic composition and the thermal treatment temperatures.     

Electrocatalysis of oxygen reduction and small alcohol oxidation in alkaline media

We present here a critical review of several technologically important electrocatalytic systems operating in alkaline electrolytes. These include the oxygen reduction reaction (ORR) occurring on catalysts containing Pt, Pd, Ir, Ru, or Ag, the methanol oxidation reaction (MOR) occurring on Pt-containing catalysts, and the ethanol oxidation reaction (EOR) occurring on Ni-Co-Fe alloy catalysts. Each of these catalytic systems is relevant to alkaline fuel cell (AFC) technology, while the ORR systems are also relevant to chlor-alkali electrolysis and metal-air batteries. The use of alkaline media presents advantages both in electrocatalytic activity and in materials stability and corrosion. Therefore, prospects for the continued development of alkaline electrocatalytic systems, including alkaline fuel cells, seem very promising.     

Smart synthesis of hollow core mesoporous shell carbons (HCMSC) as effective catalyst supports for methanol oxidation and oxygen reduction reactions

The present paper describes an easy and quick synthesis of hollow core mesoporous shell carbon (HCMSC) simply templated from unpretreated solid core mesoporous shell silica using a cheap precursor like sucrose. Physical characterizations showed uniform spherical carbon capsules with a hollow macroporous core of ca. 305- and 55-nm-thick mesoporous shell, forming a well-developed 3-D interconnected bimodal porosity. High specific surface area and large pore volume were also confirmed, suggesting the obtained HCMSC as a promising catalyst support. HCMSC-supported Pt (nominal 20 wt.%) with an average Pt particle size of 1.9 nm was synthesized by wet impregnation, and a signal of strong interaction between carbon support and platinum was confirmed by X-ray photoelectron spectroscopy. In cyclic voltammetry and linear sweep voltammetry tests, the Pt/HCMSC electrode showed significantly higher electrocatalytic activity for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) if compared with commercial Pt/Vulcan catalyst. The durability tests by cyclic voltammetry showed for the Pt/HCMSC a lower electrochemical active surface area loss than the commercial one in acidic solution. All the primary tests suggested that the Pt/HCMSC, due to its particular structure and the high dispersion of noble metal particles, is a promising catalyst for fuel cell applications, for MOR and ORR.     

Sonochemical synthesis of graphene oxide supported Pt–Pd alloy nanocrystals as efficient electrocatalysts for methanol oxidation

Pt–Pd bimetallic nanoparticles supported on graphene oxide (GO) nanosheets were prepared by a sonochemical reduction method in the presence of polyethylene glycol as a stabilizing agent. The synthetic method allowed for a fine tuning of the particle composition without significant changes in their size and degree of aggregation. Detailed characterization of GO-supported Pt–Pd catalysts was carried out by transmission electron microscopy (TEM), AFM, XPS, and electrochemical techniques. Uniform deposition of Pt–Pd nanoparticles with an average diameter of 3 nm was achieved on graphene nanosheets using a novel dual-frequency sonication approach. GO-supported bimetallic catalyst showed significant electrocatalytic activity for methanol oxidation. The influence of different molar compositions of Pt and Pd (1:1, 2:1, and 3:1) on the methanol oxidation efficiency was also evaluated. Among the different Pt/Pd ratios, the 1:1 ratio material showed the lowest onset potential and generated the highest peak current density. The effect of catalyst loading on carbon paper (working electrode) was also studied. Increasing the catalyst loading beyond a certain amount lowered the catalytic activity due to the aggregation of metal particle-loaded GO nanosheets.     

A simple one-step preparation of high utilization AuPt nanoparticles supported on MWCNTs for methanol oxidation in alkaline medium

A simple one-step preparation of gold–platinum electrocatalysts supported on multi-walled carbon nanotubes (MWCNTs) with high utilization is reported. A low Pt loading series of bimetallic AuPt/MWCNTs catalysts were prepared by the improved ethylene glycol reduction method, and then they were compared in terms of the electrocatalytic activity for methanol oxidation using cyclic voltammetry (CV) and chronoamperometry in alkaline solutions. The structure of AuPt/MWCNTs was characterized by the transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The results showed high Pt utilization, uniform AuPt nanoparticles size and good electrocatalytic activity for methanol electro-oxidation. The effect of Au/Pt mass ratio on electrocatalytic activity was also investigated by CV and chronoamperometry. The highest peak current density, lowest onset potential and best anti-poisoning effect for methanol electro-oxidation appeared at the Au/Pt/MWCNTs mass ratio of 2:4:32.     

Structural and Electronic Effects of Carbon‐Supported PtxPd1−x Nanoparticles on the Electrocatalytic Activity of the Oxygen‐Reduction Reaction and on Methanol Tolerance

We report a systematic investigation on the structural and electronic effects of carbon‐supported Pt_xPd_1?x bimetallic nanoparticles on the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acid electrolyte. Pt_xPd_1?x/C nanocatalysts with various Pt/Pd atomic ratios (x=0.25, 0.5, and 0.75) were synthesized by using a borohydride‐reduction method. Rotating‐disk electrode measurements revealed that the Pt₃Pd₁/C nanocatalyst has a synergistic effect on the ORR, showing 50 % enhancement, and an antagonistic effect on the MOR, showing 90 % reduction, relative to JM 20 Pt/C on a mass basis. The extent of alloying and Pt d‐band vacancies of the Pt_xPd_1?x/C nanocatalysts were explored by extended X‐ray absorption fine‐structure spectroscopy (EXAFS) and X‐ray absorption near‐edge structure spectroscopy (XANES). The structure–activity relationship indicates that ORR activity and methanol tolerance of the nanocatalysts strongly depend on their extent of alloying and d‐band vacancies. The optimal composition for enhanced ORR activity is Pt₃Pd₁/C, with high extent of alloying and low Pt d‐band vacancies, owing to favorable O? O scission and inhibited formation of oxygenated intermediates. MOR activity also shows structure dependence. For example, Pt₁Pd₃/C with Pt_rich?corePd_rich?shell structure possesses lower MOR activity than the Pt₃Pd₁/C nanocatalyst with random alloy structure. Herein, extent of alloying and d‐band vacancies reveal new insights into the synergistic and antagonistic effects of the Pt_xPd_1?x/C nanocatalysts on surface reactivity.     

Self-assembly of mixed Pt and Au nanoparticles on PDDA-functionalized graphene as effective electrocatalysts for formic acid oxidation of fuel cells

Pt and Au nanoparticles with controlled Pt?:?Au molar ratios and PtAu nanoparticle loadings were successfully self-assembled onto poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (PDDA-G) as highly effective electrocatalysts for formic acid oxidation in direct formic acid fuel cells (DFAFCs). The simultaneously assembled Pt and Au nanoparticles on PDDA-G showed superb electrocatalytic activity for HCOOH oxidation, and the current density associated with the preferred dehydrogenation pathway for the direct formation of CO(2) through HCOOH oxidation on a Pt(1)Au(8)/PDDA-G (i.e., a Pt?:?Au ratio of 1?:?8) is 32 times higher than on monometallic Pt/PDDA-G. The main function of the Au in the mixed Pt and Au nanoparticles on PDDA-G is to facilitate the first electron transfer from HCOOH to HCOO(ads) and the effective spillover of HCOO(ads) from Au to Pt nanoparticles, where HCOO(ads) is further oxidized to CO(2). The Pt?:?Au molar ratio and PtAu nanoparticle loading on PDDA-G supports are the two critical factors to achieve excellent electrocatalytic activity of PtAu/PDDA-G catalysts for the HCOOH oxidation reactions.     

Facile single-step preparation of Pt/N-graphene catalysts with improved methanol electrooxidation activity

In this work, we describe a facile single-step approach for the simultaneous reduction of graphene oxide to graphene, functional doping of graphene with nitrogen, and loading of the doped graphene with well-dispersed platinum (Pt) nanoparticles using a solvent mixture of ethylene glycol and N-methyl-2-pyrrolidone. The as-prepared Pt/nitrogen-doped graphene (N-graphene) catalysts are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy while the electrocatalytic methanol oxidation properties of the catalysts are evaluated by cyclic voltammetry and chronoamperometry. Compared with an updoped Pt/graphene control catalyst, the Pt/N-graphene catalyst shows a narrower particle size distribution and improved catalytic performance. Considering the facile, green and effective single-step synthetic process for the Pt/N-graphene catalyst, the results are promising for the potential application of these materials in emerging fuel cell technologies.     

Pt-decorated PdCo@Pd/C core-shell nanoparticles with enhanced stability and electrocatalytic activity for the oxygen reduction reaction

A simple method for the preparation of PdCo@Pd core-shell nanoparticles supported on carbon based on an adsorbate-induced surface segregation effect has been developed. The stability of these PdCo@Pd nanoparticles and their electrocatalytic activity for the oxygen reduction reaction (ORR) were enhanced by decoration with a small amount of Pt deposited via a spontaneous displacement reaction. The facile method described herein is suitable for large-scale, lower-cost production and significantly lowers the Pt loading and thus the cost. The as-prepared PdCo@Pd and Pd-decorated PdCo@Pd nanocatalysts have a higher methanol tolerance than Pt/C in the ORR and are promising cathode catalysts for fuel cell applications.     

Pt–Fe cathode catalysts to improve the oxygen reduction reaction and methanol tolerance in direct methanol fuel cells

High surface area carbon-supported Pt and bimetallic Pt–Fe catalysts are investigated for the oxygen electro-reduction reaction (ORR) in low-temperature direct methanol fuel cells (60 °C). The electrocatalysts are prepared using a combination of colloidal and incipient wetness methods allowing the synthesis of carbon-supported bimetallic nanoparticles with a particle size of about 2–3 nm. These materials are studied in terms of structure, morphology and composition using X-ray diffraction, X-ray fluorescence and transmission electron microscopy techniques. The electrocatalytic behaviour of these catalysts for ORR is investigated by employing the rotating disc technique. An enhancement of the ORR is observed with the bimetallic Pt–Fe catalyst in the oxygen-saturated electrolyte solution, with and without methanol. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

Preparation and electrochemical performance of graphene–Pt black nanocomposite for electrochemical methanol oxidation

This work reports the preparation, characterization, and electrocatalytic characteristics of a new metallic nanocatalyst. The catalyst, Pt black–graphene oxide (Pt-GO), was prepared by deposition of Pt black on the surface of graphene oxide nanosheet and characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and voltammetry. The Pt-graphene (Pt-GR) composite modified glassy carbon electrode (Pt-GR/GCE) was prepared with cyclic voltammetric scanning of Pt-GO/GCE in the potential range from ?1.5 to 0.2 in 0.1 M phosphate buffer solution at 50 mV·s^?1 for 5 cycles. The electrocatalytic properties of the Pt-GR/GCE for methanol (CH₃OH) oxidation have been investigated by cyclic voltammetry (CV); high electrocatalytic activity of the Pt-GR/GCE can be observed. This may be attributed to the high dispersion of Pt catalyst and the particular properties of GR support. The long-term stability of Pt-GR composite was investigated in 0.05 M CH₃OH in 0.1 M H₂SO₄ solution. It can be observed that the peak current decreases gradually with the successive scans. The loss may result from the consumption of methanol during the CV scan. It also may be due to the poisoning organic compounds. The results imply that the Pt-GR composite has good potential applications in fuel cells.     

One-pot fabrication of single-crystalline octahedral Pd-Pt nanocrystals with enhanced electrocatalytic activity for methanol oxidation

This study reports the synthesis of octahedral Pd-Pt bimetallic alloy nanocrystals through a facile, one-pot, templateless, and seedless hydrothermal method in the presence of glucose and hexadecyl trimethyl ammonium bromide. The morphologies, compositions, and structures of the Pd-Pt nanocrystals were fully characterized by various physical techniques, thereby demonstrating their highly alloying octahedral nanostructures. The formation or growth mechanism of the Pd-Pt bimetallic alloy nanocrystals was explored and is discussed here based on the experimental observations. In addition, the synthesized Pd-Pt nanocrystals were applied to the methanol oxidation reaction (MOR) in alkaline media, which proved that the as-prepared catalysts exhibit enhanced electrocatalytic activity for MOR. Pd₁Pt₃ exhibited the best stability and durability, and its mass activity was 3.4 and 5.2 times greater than those of Pt black and Pd black catalysts, respectively. The facile synthetic process and excellent catalytic performance of the as-prepared catalysts demonstrate that they have the potential to be used in direct methanol fuel cell techniques.     

Platinum nanoparticles coated by graphene layers: A low-metal loading catalyst for methanol oxidation in alkaline media

Platinum catalysts play a major role in the large scale commercialization of direct methanol fuel cells(DMFC). Here, we present a procedure to create a nanostructural graphene-platinum(Gr Pt) composite containing a small amount(5.3 wt%) of platinum nanoparticles coated with at least four layers of graphene. The composite, as Gr Pt ink, was deposited on a glassy carbon electrode and its electrocatalytic activity in a methanol oxidation reaction(MOR) was evaluated in a 1 M CH_3 OH/1 M Na OH solution. The results indicated an enhanced catalytic performance of Gr Pt towards MOR in alkaline media compared with the Pt/C material. Electron energy-loss spectroscopy and X-ray photoelectron spectroscopy(recorded before and after the electrochemical assays) were employed to analyze the changes in the chemical composition of the nanomaterial and to explain the transformations that took place at the electrode surface.Our findings suggest that growing of graphene on platinum nanoparticles improve the catalytic performance of platinum-graphene composites towards MOR in alkaline media.     

High performance Fe and N-codoped graphene quantum dot supported Pd3Co catalyst with synergistically improved oxygen reduction activity and great methanol tolerance

Designing high-performance and durable non-platinum catalysts as oxygen reduction reaction (ORR) catalysts is still a major barrier of fuel cell commercialization. In this work, simple hydrothermal and impregnation routes were applied to prepare non-platinum Pd-Co bimetallic nano-catalysts such as Fe-N doped graphene quantum dot (Fe-N-GQD) supported Pd₃Co (Pd₃Co/Fe-N-GQD 10 wt%), carbon supported Pd₃Co/C (10 wt%), graphene quantum dot supported Pd₃Co/C (10 wt%). The synthesized catalysts were physico-chemically characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electronmicroscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical investigation was carried out in three electrode half-cell system to evaluate the catalyst activity for oxygen reduction reaction (ORR), the tolerance to methanol crossover and durability. In comparison to commercial Pt/C (ETEK, 20 wt%), the Pd₃Co/Fe-N-GQD with lower weight percentage catalyst (∼10 wt%) displayed comparable electrocatalytic activity toward ORR with even higher methanol-tolerance capability and durability. The fabricated Pd₃Co/Fe-N-GQD with (10 wt %) metal loading exhibited only 20% lower activity than Pt/C (ETEK, 20 wt%) toward ORR. Nevertheless the durability study of the catalyst in acidic media showed that the Pd₃Co/Fe-N-GQD preserve 40% of its activity while Pt/C (ETEK, 20 wt%) exhibited only 20% of its initial catalytic activity for ORR. Moreover the activity loss in the presence of methanol (0.1 M) was obtained for Pt/C (ETEK, 20 wt%) and Pd₃Co/Fe-N-GQD 35% and 14%, respectively. To investigate the role of catalyst support, catalytic activities of Pd₃Co/Fe-N-GQD, Pd₃Co/C, Pd₃Co/GQD and Pd/Fe-N-GQD were compared. The results demonstrated superior catalytic activity of Pd₃Co/Fe-N-GQD which could be related to the cocatalytic role of Fe-N-GQD due to the presence numerous of active sites exposed to the reactants.     

一步法制备还原态氧化石墨烯载铂纳米粒子及其对甲醇氧化的电催化性能

以天然石墨为原料,采用改进的Hummers法制备氧化石墨.然后采用简单的一步化学还原法在乙二醇(EG)中同时还原氧化石墨烯(GO)和H₂PtCl₆制备高分散的铂/还原态氧化石墨烯(Pt/RGO)催化剂.采用傅里叶变换红外(FTIR)光谱、X射线衍射(XRD)和透射电子显微镜(TEM)对催化剂的微结构、组成和形貌进行表征.结果表明, GO已被还原成RGO, Pt纳米粒子均匀分散在RGO表面,粒径约为2.3 nm.采用循环伏安法和计时电流法评价催化剂对甲醇氧化的电催化性能,测试结果表明, Pt/RGO催化剂对甲醇氧化的电催化活性和稳定性与Pt/C和Pt/CNT相比有了很大提高.另外其对甲醇电催化氧化的循环伏安图中正扫峰电流密度(I_f)和反扫峰电流密度(I_b)的比值高达1.3,分别是Pt/C和Pt/CNT催化剂的2.2和1.9倍,表明Pt/RGO催化剂具有高的抗甲醇氧化中间体CO_ad的中毒能力.     

壳聚糖修饰炭黑负载Pt-Au催化剂对甲醇氧化的电催化性能

以炭黑及自制的壳聚糖-炭黑(CHI-C)复合材料为载体,采用溶胶负载法制备了Pt_m＾Au/C及Pt_m＾Au/CHI-C催化剂(＾ 代表Au、Pt为分步负载,m代表Pt/Au原子比),通过紫外-可见吸收光谱、X射线衍射、透射电镜及X射线光电子能谱对催化剂进行了表征。利用循环伏安法和计时电流法分别测定了Pt-Au催化剂对甲醇电催化氧化反应的活性和稳定性,考查了Pt/Au原子比及CHI改性对电催化活性和稳定性的影响。结果表明,Pt_1.0＾Au/C具有最高的催化活性,炭黑中加入少量CHI能提高Pt_1.0＾Au/C催化剂的稳定性。     

Direct Growth of Single‐Crystal Pt Nanowires on Sn@CNT Nanocable: 3D Electrodes for Highly Active Electrocatalysts

A newly designed and fabricated novel three dimensional (3D) nanocomposite composed of single‐crystal Pt nanowires (PtNW) and a coaxial nanocable support consisting of a tin nanowire and a carbon nanotube (Sn@CNT) is reported. This nanocomposite is fabricated by the synthesis of Sn@CNT nanocables by means of a thermal evaporation method, followed by the direct growth with PtNWs through a facile aqueous solution approach at room temperature. Electrochemical measurements demonstrate that the PtNW? Sn@CNT 3D electrode exhibits enhanced electrocatalytic performance in oxygen reduction reaction (ORR) for polymer electrolyte membrane fuel cells (PEMFCs), methanol oxidation (MOR) for direct methanol fuel cells (DMFCs), and CO tolerance compared with commercial ETEK Pt/C catalyst made of Pt nanoparticles.