Effect of third metal on the electrocatalytic activity of PtRu/Vulcan for methanol electro-oxidation

The effect of a third metal on the activity of PtRu/Vulcan toward methanol oxidation reaction (MOR) is studied. An efficient method to prepare ternary catalysts was used, which allows the introduction of the third metal to PtRu/Vulcan without altering its particle size or dispersion. Ni, Mo, Co, and Ir were chosen and added to PtRu/Vulcan, based on theoretical and experimental literature results, anticipating enhancement in the catalytic activity of PtRu/Vulcan. The composition of the third metal can be varied from trace to considerable amounts. Transmission electron microscopy and energy-dispersive X-ray analysis were used to determine the particle size, dispersion, and the composition of the ternary catalysts. Cylic voltammetry, chronoamperometry, and CO-stripping voltammetry were used to analyze and compare the activities of the catalysts at 25 °C. It has been found that the addition of even trace amounts of third metal significantly affects the catalytic activity of PtRu toward MOR.     

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。     

大麻杆生物质碳负载Pt用于电催化氧化甲醇

首先以大麻杆为前驱体,利用化学活化法,在氮气保护下高温炭化制备多孔结构碳材料。利用扫描电镜、X射线粉末衍射、氮吸脱附实验等探究温度和碱碳比对碳材料结构和孔径分布的影响。结果表明:当温度一定时,随着碱碳比增大比表面积呈抛物线上升。在碱碳比一定的情况下,温度升高,比表面积明显增大,比表面积可达1622.10 m²·g^-1。然后,利用光还原法,以大麻杆碳材料为载体,磷钨酸为光催化还原剂、稳定剂和包覆剂,异丙醇作供电子体,在紫外光的照射下一步合成多酸基@Pt大麻杆碳复合材料并考察其电化学性能。研究表明此复合材料电催化氧化甲醇得到峰电流密度为4.87 mA·cm^-2,表现出了较好的催化活性和稳定性。     

Highly active PtRuFe/C catalyst for methanol electro-oxidation

High methanol electro-oxidation activity was obtained on novel PtRuFe/C (2:1:1 at.%) catalyst. Mass and specific activities were 5.67 A  g⁻¹ catal. and 177 mA m⁻² for the PtRuFe/C catalyst while those of the commercial PtRu/C catalyst were 2.28 A g⁻¹ catal. and 87.7 mA m⁻², respectively. CO stripping results showed that on-set voltage for CO electro-oxidation was lowered by incorporation of Fe. XRD and XPS results revealed that Fe₂O₃ was formed instead of Fe(0), which resulted in large electron deficiency in Pt and easy CO electro-oxidation. The electron deficiency of Pt was proved by XPS results of Pt4f peaks, which moved to higher binding energies in PtRuFe/C than PtRu/C.     

Anodic activation of PtRu/C catalysts for methanol oxidation

Anodic treatment of PtRu/C catalysts in 0.5 M sulfuric acid at 1.3 V (vs RHE) for 0.5 h was found able to promote the activity for methanol oxidation by a few tenths to 5 times. This anodic activation effect was valid for samples domestically prepared under different conditions and that produced by Johnson-Matthey. On the basis of the changes of cyclic voltammetry during the anodic treatment, a model was proposed for the activation effect. According to the model, there are two categories of ruthenium oxides in the catalyst: one is electrochemically reversible and beneficial for catalytic activity, while the other is irreversible and harmful. During the anodic treatment, the harmful oxide is decreased, while the beneficial oxide either increased or changed only slightly, resulting in a beneficial net change.     

Enhanced stability and activity of PtRu nanotubes for methanol electrooxidation

PtRu 1D nanostructures on titanium are prepared and analysed as electrocatalysts for methanol electrooxidation. The morphology and composition of the 1D nanostructure are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrocatalytic properties of such catalysts for methanol oxidation are investigated by cyclic voltammetry (CV) and chronoamperometry (CA) in 1.0 M CH₃OH + 0.5 M H₂SO₄ aqueous solution. The results show that Pt₄₆Ru₅₄ nanotubes yields to a five-fold improvement of the mass specific activity and to a three-fold improvement of the long-term poisoning rate as compared to PtRu black of similar composition.     

Graphene supported electrocatalysts for methanol oxidation

Graphene nanosheet was prepared by modified Hummer’s chemical method and utilized as a catalyst support of PtRu nanoparticles for the electro-oxidation of methanol. Home-made graphene nanosheet was clearly characterized by Raman spectroscopy and we applied colloidal method to synthesize with high metal content of 80 wt.% Pt–Ru catalyst, which is extensively clarified by HR-TEM and XRD analysis. 80 wt.% Pt–Ru/graphene nanosheet catalyst showed superior electrochemical activity toward methanol oxidation compared to Pt–Ru/Vulcan XC-72R. It is due to the significant increase of electrochemical active surface area for better catalyst utilization.     

Ultrathin platinum film covered high-surface-area nanoporous gold for methanol electro-oxidation

An ultrathin platinum film is fabricated on a nanoporous gold (NPG) scaffold through a catalytic chemical deposition method. The morphology and active surface area of the deposited Pt film, which will greatly influence the electro-catalytic properties of the catalyst, can be controlled by adjusting the deposition condition. Compared with bare NPG and high Pt loaded NPG, the performances of methanol electro-oxidation on the low-Pt-content bimetallic film are greatly improved, both in its catalytic current enhancement and signal stability. The best condition for methanol oxidation can be achieved when the area ratio of deposited Pt and uncovered Au was 3:1.     

Polyoxometalate-modified carbon nanotubes: new catalyst support for methanol electro-oxidation

A new catalyst support, polyoxometalate-modified carbon nanotubes, is presented in this paper through the chemisorption between polyoxometalate and carbon. Pt and Pt-Ru nanoparticles were electrochemically deposited on polyoxometalate-modified carbon nanotubes electrodes, and their electrocatalytic properties for methanol electro-oxidation are investigated in detail. Due to the unique electrical properties of carbon nanotubes and the excellent redox properties and the high protonic conductivity of polyoxometalate, for the similar deposition charge of Pt and Pt-Ru catalysts, 1.4 times larger exchange current density, 1.5 times higher specific activity, and better cycle stabilities can be obtained at polyoxometalate-modified carbon nanotube electrodes as compared to the electrodes without polyoxometalate modification. These results show that polyoxometalate-modified carbon nanotubes as a new catalyst support have good potential application in direct methanol fuel cells.     

Solvent effects on Pt-Ru/C catalyst for methanol electro-oxidation

Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent(s) used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry (CV) and Chronoamperometry (CA). Pt-Ru/C catalyst prepared in H₂O or binary solvents of H₂O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.     

Adsorbed water for the electro-oxidation of methanol at Pt-Ru alloy

Adsorbed water molecules which promote the methanol oxidation reaction (MOR) at Pt-Ru alloy electrode are clearly detected by in-situ FTIR spectroscopy with the attenuated total reflection configuration, which directly supports the "bi-functional mechanism" for the MOR.     

CO tolerant Pt/WC methanol electro-oxidation catalyst

Platinum supported on WC (Pt/WC) catalyst (20 wt.% Pt) was synthesized as a new methanol electro-oxidation catalyst. Particle size of 7.5 nm was obtained from X-ray diffraction results and a uniform distribution of particles was observed by transmission electron microscopy. In cyclic voltammetry (CV) measurement, the reduction peak potential of PtO increased from 0.72 V in commercial Pt/C to 0.76 V in Pt/WC. By combining the CV and CO stripping results, spill-over of H⁺ from Pt to WC was observed. Electrochemically active surface area calculated from the desorption area of H⁺ were 11.2 and 5.74 m²/g catalyst for Pt/WC and Pt/C, while those obtained from the desorption area of CO were 4.42 and 6.40 m²/g catalyst, respectively. CO electro-oxidation peak potential greatly decreased from 0.80 V in Pt/C to 0.68 V in Pt/WC. The reaction of WC with water to produce WC–OH could lower to CO electro-oxidation peak potential. Specific activity for methanol electro-oxidation increased from 144 mA/m² in Pt/C to 188 mA/m² in Pt/WC.     

Pt/C nanocatalysts for methanol electrooxidation prepared by water-in-oil microemulsion method

Journal of Solid State Electrochemistry - Pt nanoparticles supported on Vulcan XC-72R were synthesized by water-in-oil microemulsion method. By incorporating different amounts of HCl as a capping...     

Structural analysis of sonochemically prepared PtRu versus Johnson Matthey PtRu in operating direct methanol fuel cells

Sonochemically prepared PtRu (3 : 1) and Johnson Matthey PtRu (1 : 1) were analyzed by X-ray absorption spectroscopy in operating liquid feed direct methanol fuel cells. The total metal loadings were 4 mg cm(-2) unsupported catalysts at the anode and cathode of the membrane electrode assembly. Ex situ XRD lattice parameter analysis indicates partial segregation of the Ru from the PtRu fcc alloy in both catalysts. A comparison of the in situ DMFC EXAFS to that of the as-received catalyst shows that catalyst restructuring during DMFC operation increases the total metal coordination numbers. A combined analysis of XRD determined grain sizes and lattice parameters, ex situ and in situ EXAFS analysis, and XRF of the as-received catalysts enables determination of the catalyst shell composition. The multi-spectrum analysis shows that the core size increases during DMFC operation by reduction of Pt oxides and incorporation of Pt into the core. This increases the mole fraction of Ru in the catalyst shell structure.     

Electrospun bimetallic nanowires of PtRh and PtRu with compositional variation for methanol electrooxidation

Binary metallic nanowires (NWs) of PtRh and PtRu were synthesized by electrospinning method with compositional variation from 1:3 to 2:1. The electrospun bimetallic NWs were highly alloyed with diameters smaller than 60 nm and lengths up to hundreds of micrometers. The PtRh and PtRu NWs with 1:1 atomic ratio resulted in the higher catalytic mass activity over the methanol electrooxidation than those with the different atomic ratios, and the mass activity of Pt₁Ru₁ NWs was superior to the other NWs and even better than the commercial catalyst of the highly dispersed Pt₁Ru₁ nanoparticles on carbon. Moreover, the bimetallic NW electrocatalysts showed the better stability than the bimetallic nanoparticles. The enhancements of electrocatalytic properties for the Pt₁Rh₁ and Pt₁Ru₁ NWs could be attributed to their one-dimensional features, which can outperform on the electro-oxidations over the fuel cell electrodes.     

Investigation of Pt–Ru nanoparticle catalysts for low temperature methanol electro-oxidation

Pt–Ru nanoparticle-based methanol electro-oxidation catalysts with high concentration of metallic phase on carbon black have been synthesised by a low-temperature colloidal preparation route. Amorphous Pt–Ru oxide nanoparticles were deposited on carbon and subsequently reduced in hydrogen stream at different temperatures to obtain crystalline phases with tailored particle size. The electro-catalytic activity for methanol oxidation was investigated in half-cell from 30 to 60 °C. The results were interpreted in terms of particle size, crystallographic structure, degree of alloying and carbon monoxide adsorption properties. The best performance was achieved for the catalyst with intermediate particle size in the investigated range. Furthermore, it is observed that the optimal properties for these catalysts depend on the operating temperature.     

Multiwalled carbon nanotube supported PtRu for the anode of direct methanol fuel cells

The activity of the methanol oxidation reaction of a multiwalled carbon nanotube (MWCNT)-supported PtRu catalyst was investigated and compared with the Vulcan XC-72 carbon-supported catalyst. The PtRu nanoparticles with 1:1 and 7:3 atomic ratios (with similar PtRu loadings and morphological structures) were deposited both on the MWCNTs and on the carbon. Cyclicvoltammetry results demonstrated that the MWCNT-supported PtRu catalyst exhibited a higher mass activity (mA mg(-1) of PtRu) for the methanol oxidation reaction than the carbon-supported PtRu under the condition that both catalysts possess more or less the same PtRu loadings, particle sizes, dispersions, and electrochemical surface area. The direct methanol fuel cell performance test data showed that MWCNT-supported PtRu catalysts yielded about 35-39% higher power densities than the carbon-supported PtRu.     

PtRu/氮掺杂碳电催化甲醇氧化及电解水析氢性能

将三聚氰胺、RuCl₃及炭黑以一定的比例分散于乙醇中,采用旋转蒸干及高温热处理合成了一种氮掺杂碳(NC)负载Ru的Ru/NC 催化剂。采用硼氢化钠液相化学还原法合成了不同 Pt、Ru 负载量的 PtRu/NC 催化剂,并用于电催化甲醇氧化反应(MOR)及电催化分解水析氢反应(HER)。结果表明,合成的催化剂中 Pt₁Ru/NC(Pt、Ru的实际负载量分别为 1.14%、0.54%)表现出最优的MOR性能,质量活性达4.96 A·mg^-1_PtRu,且经10 000 s稳定性测试后质量活性保持在测试前的91.1%。同时,当电流密度为100 mA·cm^-2时,Pt₁Ru/NC在HER中表现出最低的过电位(103 mV)和最小的Tafel斜率(15.29 mV·dec^-1)。通过X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、扫描透射电子显微镜(STEM)、电感耦合等离子体发射光谱(ICP‐OES)、STEM‐能谱(STEM‐EDS)技术PtRu/NC双金属催化剂,其具有优异催化性能的原因如下：(1) PtRu双金属纳米颗粒高度分散于NC上;(2) Pt以纳米团簇或单原子形式负载于Ru上,后负载于NC,形成了Pt‐Ru相分离结构;(3) Pt、Ru与N之间存在协同效应。     

Carbon nanotubes-Nafion composites as Pt-Ru catalyst support for methanol electro-oxidation in acid media

Carbon nanotubes-Nafion (CNTs-Nafion) composites were prepared by impregnated CNTs with Nafion in ethanol solution and characterized by FT-IR. Pt-Ru catalysts supported on CNTs-Nafion composites were synthesized by microwave-assisted polyol process. The physical and electrochemical properties of the catalysts were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), CO stripping voltammetry, cyclic voltammetry (CV) and chronoamperometry (CA). The results showed that the Nafion incorporation in CNTs-Nafion composites did not significantly alter the oxygen-containing groups on the CNTs surface. The Pt-Ru catalyst supported on CNTs-Nafion composites with 2 wt% Nafion showed good dispersion and the best CO oxidation and methanol electro-oxidation activities.     

{[PMo_(12)O_(40)]~(3-)-Pt/PAMAM}_n多层复合膜的制备及对甲醇的电催化氧化活性

用电化学扫描法制备了{[PMo12O40]3--Pt/PAMAM}n多层复合膜,通过X射线光电子能谱(XPS)、循环伏安测定(CV)和原子力显微镜(AFM)对样品的化学组成和膜的均匀性进行了表征。测试和分析结果表明[PMo12O40]3--Pt和PAMAM通过静电相互作用形成了交替多层复合膜,且膜的增长均匀,[PMo12O40]3-和Pt粒子均匀分布在间隔剂PAMAM上。采用三电极体系的循环伏安电化学分析方法研究了样品在酸性溶液中对甲醇的电催化氧化活性,结果表明,与Pt/GCE催化剂相比,{[PMo12O40]3--Pt/PAMAM}n/GCE呈现出较高的电催化氧化活性和好的稳定性。