Dynamics of Electrocatalytic Oxidation of Ethylene Glycol,Methanol and Formic Acid at MWCNT Platform Electrochemically Modified with Pt/Ru Nanoparticles

Comparative electrocatalytic behavior of functionalized multiwalled carbon nanotubes (fMWCNTs) electrodecorated with Pt/Ru nanoparticles towards the oxidation of methanol (MeOH), ethylene glycol (EG) and formic acid (FA) has been investigated. The catalytic current density decreased approximately as MeOH≈EG>FA. Result revealed that BPPGE‐fMWCNT‐Pt/Ru tolerates CO poisoning for FA electrooxidation than when used for the oxidation of the EG or MeOH. Electrochemical impedance spectra are dependent on the oxidation potentials, with equivalent circuit models characteristic of adsorption‐controlled charge transfer kinetics. The results provide important insights into the electrochemical response of these small organic molecules useful in fuel cell technology.     

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.     

原子层沉积制备掺氮碳膜修饰的 Pt/CNTs 实现甲醇高效电催化氧化

甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注. 贵金属 Pt 是甲醇燃料电池阳极催化剂不可缺少的活性组分, 但 Pt 价格昂贵, 易与 CO 等中间体强相互作用而中毒失活, 从而限制了甲醇燃料电池的广泛应用. 因此, 如何提高Pt 的利用率成为一个关键问题. 研究表明, 在碳材料载体中掺杂氮元素, 改变了载体本身的表面结构和电子性质, 有利于Pt 颗粒的成核和生长, 可获得尺寸小、分布均匀的 Pt 纳米颗粒, 能显著提升催化反应活性和 Pt 利用率. 然而, 传统的氮掺杂方法需要在高温、高压及氨气条件下进行, 增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术, 能够在原子级别精确控制膜的厚度, 既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰. 本课题组利用原子层沉积技术优势, 首先在碳纳米管表面沉积了直径 2 nm 左右的 Pt纳米颗粒, 然后在 Pt 纳米颗粒外表面超薄修饰聚酰亚胺膜, 通过后处理得到多孔掺氮碳膜修饰的 Pt/CNTs 催化剂. 碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制. 结果表明, 适当厚度的碳膜修饰 Pt/CNTs 催化剂可显著提升其甲醇电氧化性能, 电流密度可达商业 20% Pt/C 的 2.7 倍, 催化剂稳定性也显著改善. 然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现, 超薄修饰碳膜后催化剂活性表面积有所降低, 这是由于碳膜的覆盖导致表面 Pt原子数减少. 修饰前后催化剂颗粒尺度变化不大, 推测催化剂活性的提高与形成了有利于催化反应的 Pt-碳膜界面有关.然而, 当碳膜修饰层过厚时, 会导致反应物分子难以扩散到 Pt 颗粒表面, 使催化剂活性降低. 预吸附单层 CO 溶出实验结果表明, 多孔掺氮碳膜超薄修饰 Pt/CNTs 催化剂后, CO 氧化峰的起始电位和峰值电位都向低电位处偏移, 这表明 Pt 表面吸附的 CO 在较低电位下即可被氧化, CO 更容易从 Pt 表面移除, 从而提高了催化剂的抗 CO 毒化能力. X 射线光电子能谱实验结果进一步表明, 经多孔掺氮碳膜修饰后, Pt 的 4f 电子向高结合能处偏移, 表明 Pt 原子周围的电子密度减小, 从而弱化了 Pt 对 CO 吸附的σ-π键反馈作用, 即减弱了 Pt 原子对 CO 的吸附, 这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因.     

Nanostructure Engineering of Metal–Organic Derived Frameworks: Cobalt Phosphide Embedded in Carbon Nanotubes as an Efficient ORR Catalyst

Heteroatom doping is considered an efficient strategy when tuning the electronic and structural modulation of catalysts to achieve improved performance towards renewable energy applications. Herein, we synthesized a series of carbon-based hierarchical nanostructures through the controlled pyrolysis of Co-MOF (metal organic framework) precursors followed by in situ phosphidation. Two kinds of catalysts were prepared: metal nanoparticles embedded in carbon nanotubes, and metal nanoparticles dispersed on the carbon surface. The results proved that the metal nanoparticles embedded in carbon nanotubes exhibit enhanced ORR electrocatalytic performance, owed to the enriched catalytic sites and the mass transfer facilitating channels provided by the hierarchical porous structure of the carbon nanotubes. Furthermore, the phosphidation of the metal nanoparticles embedded in carbon nanotubes (P-Co-CNTs) increases the surface area and porosity, resulting in faster electron transfer, greater conductivity, and lower charge transfer resistance towards ORR pathways. The P-Co-CNT catalyst shows a half-wave potential of 0.887 V, a Tafel slope of 67 mV dec⁻¹, and robust stability, which are comparatively better than the precious metal catalyst (Pt/C). Conclusively, this study delivers a novel path for designing multiple crystal phases with improved catalytic performance for energy devices.     

PtRu/carbon nanotube nanocomposite synthesized in supercritical fluid: a novel electrocatalyst for direct methanol fuel cells

Platinum/ruthenium nanoparticles were decorated on carbon nanotubes (CNT) in supercritical carbon dioxide, and the nanocomposites were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM images show that the particles size is in the range of 5-10 nm, and XRD patterns show a face-centered cubic crystal structure. Methanol electrooxidation in 1 M sulfuric acid electrolyte containing 2 M methanol were studied onPtRu/CNT (Pt, 4.1 wt%; Ru, 2.3 wt%; molar ratio approximately Pt/Ru = 45:55) catalysts using cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. All the electrochemical results show that PtRu/CNT catalysts exhibit high activity for methanol oxidation which resulted from the high surface area of carbon nanotubes and the nanostructure of platinum/ruthenium particles. Compared with Pt/CNT, the onset potential is much lower and the ratio of forward anodic peak current to reverse anodic peak current is much higher for methanol oxidation, which indicates the higher catalytic activity of PtRu/CNT. The presence of Ru with Pt accelerates the rate of methanol oxidation. The results demonstrated the feasibility of processing bimetallic catalysts in supercritical carbon dioxide for fuel cell applications.     

AC impedance investigation of plating potentials on the catalytic activities of Pt nanocatalysts for methanol electrooxidation

Pt nanocatalysts supported on glassy carbon (GC) were electrochemically deposited by cyclic voltammetry (CV) with different scanning potential ranges. The lower limit of potential was fixed at −0.25 V vs. saturated calomel electrode, whereas the upper limit of potential was adjusted to be 0.0, 0.20, 0.60, and 1.0 V. Scanning electron microscopy images showed that Pt microparticles are uniformly dispersed on the GC substrate and the agglomerated microparticles are composed of numerous nanoparticles. In addition, the catalytic capabilities of Pt/GCs for methanol electrooxidation were examined by CV, chronoamperometry, and electrochemical impedance spectroscopy in a solution of 0.5 M CH₃OH and 0.5 M H₂SO₄. The results demonstrate that the catalytic activities and stabilities of Pt catalysts prepared by the potential ranges from −0.25 to both 0.60 and 1.0 V for methanol electrooxidation were higher than the others, which may be due to their higher electrochemical active surface area, lower charge transfer resistance, and more preferred Pt crystallographic orientation.     

Synthesis of Pt and Pt-Fe nanoparticles supported on MWCNTs used as electrocatalysts in the methanol oxidation reaction

This work reports a feasible synthesis of highly-dispersed Pt and Pt-Fe nanoparticles supported on multiwall carbon nanotubes (MWCNTs) without Fe and multiwall carbon nanotubes with iron (MWCNTs-Fe) which applied as electrocatalysts for methanol electrooxidation. A Pt coordination complex salt was synthesized in an aqueous solution and it was used as precursor to prepare Pt/MWCNTs, Pt/MWCNTs-Fe, and Pt-Fe/MWCNTs using FeCl₂·4NH₂O as iron source which were named S1, S2 and S3, respectively. The coordination complex of platinum (TOA)₂PtCl₆ was obtained by the chemical reaction between (NH₄)₂PtCl₆ with tetraoctylammonium bromide (TOAB) and it was characterized by FT-IR and TGA. The materials were characterized by Raman spectroscopy, SEM, EDS, XRD, TEM and TGA. The electrocatalytic activity of Pt-based supported on MWCNTs in the methanol oxidation was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Pt-Fe/MWCNTs electrocatalysts showed the highest electrocatalytic activity and stability among the tested electrocatalysts due to that the addition of ”Fe” promotes the OH species adsorption on the electrocatalyst surface at low potentials, thus, enhancing the activity toward the methanol oxidation reaction (MOR).     

Electrodeposition of Platinum Nanoparticles on Multi-Walled Carbon Nanotubes for Electrocatalytic Oxidation of Methanol

Platinum (Pt) nanoparticles were deposited at the surface of well-aligned multi-walled carbon nanotubes (MWNTs) by potential cycling between +0.50 and −0.70 V at a scanning rate of 50 mV · s⁻¹ in 5 mM Na₂PtCl₆ solution containing 0.1 M NaCl. The electrocatalytic oxidation of methanol at the nanocomposites of Pt nanoparticles/nanotubes (Pt_nano/MWNTs) has been investigated using 0.2 M H₂SO₄ as supporting electrolyte. The effects of various parameters, such as Pt loading, concentration of methanol, medium temperature as well as the stability of Pt_nano/MWNTs electrode, have been studied. Compared to glassy carbon electrode, carbon nanotube electrode significantly enhances the catalytic efficiency of Pt nanoparticles for methanol oxidation. This improvement in performance is due not only to the high surface area and the fast electron transfer rate of nanotubes but also to the highly dispersed Pt nanoparticles as electrocatalysts at the tips and the sidewalls of nanotubes.     

Synthesis of Pt and Pt-Fe nanoparticles supported on MWCNTs used as electrocatalysts in the methanol oxidation reaction

This work reports a feasible synthesis of highly-dispersed Pt and Pt-Fe nanoparticles supported on multiwall carbon nanotubes （MWCNTs） without Fe and multiwall carbon nanotubes with iron （MWCNTs-Fe） which applied as electrocatalysts for methanol electrooxidation. A Pt coordination complex salt was synthesized in an aqueous solution and it was used as precursor to prepare Pt/MWCNTs, Pt/MWCNTs-Fe, and Pt-Fe/MWCNTs using FeC12.4H20 as iron source which were named S 1, S2 and S3, respectively. The coordination complex of platinum （TOA）2PtC16 was obtained by the chemical reaction between （NH4）2PtC16 with tetraoctylammonium bromide （TOAB） and it was characterized by FT-IR and TGA. The materials were characterized by Raman spectroscopy, SEM, EDS, XRD, TEM and TGA. The electrocatalytic activity of Pt-based supported on MWCNTs in the methanol oxidation was investigated by cyclic voltammetry （CV） and chronoamperometry （CA）. Pt-Fe/MWCNTs electrocatalysts showed the highest electrocatalytic activity and stability among the tested electrocatalysts due to that the addition of ＂Fe＂ promotes the OH species adsorption on the electrocatalyst surface at low potentials, thus, enhancing the activity toward the methanol oxidation reaction （MOR）.     

Electrocatalytic oxidation of methanol on carbon ceramic electrode modified by platinum nanoparticles incorporated in poly (o-phenylenediamine) film

Carbon ceramic electrode, a new electrode substrate, was prepared by sol–gel procedure and used for the electropolymerization of o-phenylenediamine and incorporation of platinum nanoparticles into the resulting poly(o-phenylenediamine) (PoPD) film. The modified electrode was used for electrooxidation of methanol in 0.3 M H₂SO₄ as supporting electrolyte. The presence of PoPD film increased considerably the efficiency of deposited Pt nanoparticles toward the electrocatalytic oxidation of methanol. The effective parameters on the electrooxidation of methanol, i.e., amounts of polymer and Pt catalyst, medium temperature, working potential limit in anodic direction, and potential scan rate, were investigated, and the results were discussed.     

Controllable pt nanoparticle deposition on carbon nanotubes as an anode catalyst for direct methanol fuel cells

We report a novel process to prepare well-dispersed Pt nanoparticles on CNTs. Pt nanoparticles, which were modified by the organic molecule triphenylphosphine, were deposited on multiwalled carbon nanotubes by the organic molecule, which acts as a cross linker. By manipulating the relative ratio of Pt nanoparticles and multiwalled carbon nanotubes in solution, Pt/CNT composites with different Pt content were achieved. The so-prepared Pt/CNT composite materials show higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation than the commercial E-TEK catalyst, which can be ascribed to the high dispersion of Pt nanoparticles on the multiwalled carbon nanotube surface.     

Preparation of Pt/MWCNTs Catalyst by Taguchi Method for Electrooxidation of Nitrite

Abstract—The Pt nanoparticles-functionalized multiwall carbon nanotubes (f-MWCNTs) modified glassy carbon electrodes were used to study the electrooxidation of nitrite. Pt nanoparticles were electrodeposited on the f-MWCNTs modified glassy carbon (GC) electrode by applying a constant potential to the electrode for a specific time. By applying optimized conditions (using Minitab software), Pt/MWCNTs/GC electrode was prepared by immobilizing 40 μL of f-MWCNTs on the GC electrode and applying a potential of–0.20 V vs. Ag/AgCl for 120 s. The electrooxidation of nitrite was studied on the prepared electrode in 0.1 M KCl solution. The amperometric response of the prepared electrode linearly changes with the concentration of nitrite from 4.0 μM to 2.4 mM. The detection limit of the electrode was found to be 1.5 μM (S/N = 3) with a sensitivity of 28.7 μA/mM.     

Carbon monoxide-controlled synthesis of surface-clean Pt nanocubes with high electrocatalytic activity

A new strategy for synthesis of Pt nanocubes on various supports by reduction of a Pt precursor under a CO atmosphere was described. The as-prepared Pt nanocubes supported on multi-walled carbon nanotubes exhibited high activity toward methanol electrooxidation.     

Carbon‐Coated and Interfacial‐Functionalized Mixed‐Phase MoxTi1−xO2‐δ Nanotubes as Highly Active and Durable PtRu Catalyst Support for Methanol Electrooxidation

A synchronous carbon‐coating and interfacial‐functionalizing approach is proposed for the fabrication of Mo‐doped Mo_xTi_1?xO_2‐δ nanotubes (C@IF‐MTNTs) under mild hydrothermal reaction with subsequent annealing as advanced catalyst supports for PtRu nanoparticles (NPs) towards methanol electrooxidation. The carbonation of glucose and Mo‐doping takes place simultaneously at the interface of pristine anatase TiO₂ nanotubes (TNTs), generating a unique concentric multilayered one‐dimensional (1D) structure with crystalline an anatase/rutile mixed‐phase TiO₂ core and Mo‐functionalized interface and subsequently a carbon shell. The obtained PtRu/C@IF‐MTNTs catalyst exhibits an over 2 times higher mass activity with comparable durability than that of the unmodified PtRu/C@TNTs catalyst and over 1.7 times higher mass activity with over 20 % higher stability than that of PtRu/C catalyst. Such superior catalytic performance towards methanol electrooxidation is ascribed to the Mo‐functionalized interface, concentric multilayered 1D architecture, and anatase/rutile mixed‐phase core, which facilitates the charge transport through 1D structural support and electronic interaction between C@IF‐MTNTs and ultrafine PtRu NPs. This work reveals the critical application of a 1D interfacial functionalized architecture for advanced energy storage and conversion.     

In-situ X-ray absorption spectroscopy study of Pt and Ru chemistry during methanol electrooxidation

Methanol electrooxidation in a 0.5 M sulfuric acid electrolyte containing 1.0 M CH3OH was studied on 30% Pt/carbon and 30% PtRu/carbon (Pt/Ru = 1:1) catalysts using X-ray absorption spectroscopy (XAS). Absorption by Pt and Ru was measured at constant photon energy in the near edge region during linear potential sweeps of 10-50 mV/s between 0.01 and 1.36 V vs rhe. The absorption results were used to follow Pt and Ru oxidation and reduction under transient conditions as well as to monitor Ru dissolution. Both catalysts exhibited higher activity for methanol oxidation at high potential following multiple potential cycles. Correlation of XAS data with the potential sweeps indicates that Pt catalysts lose activity at high potentials due to Pt oxidation. The addition of Ru to Pt accelerates the rate of methanol oxidation at all potentials. Ru is more readily oxidized than Pt, but unlike Pt, its oxidation does not result in a decrease in catalytic activity. PtRu/carbon catalysts underwent significant changes during potential cycling due to Ru loss. Similar current density vs potential results were obtained using the same PtRu/carbon catalyst at the same loading in a membrane electrode assembly half cell with only a Nafion (DuPont) solid electrolyte. The results are interpreted in terms of a bifunctional catalyst mechanism in which Pt surface sites serve to chemisorb and dissociate methanol to protons and carbon monoxide, while Ru surface sites activate water and accelerate the oxidation of the chemisorbed CO intermediate. PtRu/carbon catalysts maintain their activity at very high potentials, which is attributed to the ability of the added Ru to keep Pt present in a reduced state, a necessary requirement for methanol chemisorption and dissociation.     

Synthesis of Pt/C Electrocatalysts Under Protection of Glucose and Their Improved Methanol Electrooxidation Activity

Carbon supported Pt(Pt/C) electrocatalysts were prepared with glucose as protection agent and NaBH₄ as reductant. The Pt nanoparticles deposited on carbon support presented reduced size and well dispersity attributed to the protection effect of glucose. Glucose absorbed on the particle surface was readily removed by water washing without leading to agglomeration of the Pt nanoparticles. The as-prepared Pt/C electrocatalysts showed improved mass activity for methanol electrooxidation compared to the catalyst prepared without glucose protection. The improved performance is attributed to the larger electrochemical active surface area thus increased active sites on the Pt/C elctrocatalysts prepared under the protection of glucose.     

Nitrogen-doped mesoporous carbon nanospheres loaded with cobalt nanoparticles for oxygen reduction and Zn–air batteries

Mesoporous carbon supported with transition metals nanoparticles performs desired activities for oxygen reduction reaction (ORR) and clean energy conversion devices such as Zn–air batteries. In this work, we synthesized N-doped mesoporous carbon loaded with cobalt nanoparticles (CoMCN) through self-assembly method. There are sufficient mesopores on the carbon substrate which stem from the pore-forming agent. These mesopores can provide enough accessible active sites and profitable charge/mass transport for ORR. The high content of pyridinic and graphitic N is beneficial for promoting O₂ adsorption and reduction. The smaller value of I_D/I_G indicates the higher degree of graphitization of CoMCN, providing better electronic conductivity. The half-wave potential of CoMCN is 0.865 V in basic solution, which is 24 mV more positive than that of the commercial Pt/C (0.841 V). In addition, CoMCN performs excellent methanol tolerance and stability under both basic and acidic conditions. The Zn–air battery assembled with CoMCN performs the larger power density and open-circuit voltage than the commercial Pt/C-based battery, indicating the potential application in energy conversion systems. This work provides thoughtful ideas for fabricating transition metal nanoparticles based porous carbon for electrocatalysis and metal–air batteries.     

Preparation of carbon-supported core-shell Au-Pt nanoparticles for methanol oxidation reaction: The promotional effect of the Au core

Core-shell Au-Pt nanoparticles with intimate contact of Pt and Au were prepared by a displacement reaction without formation of monometallic Au nanoparticles. The Au-Pt nanoparticles were dispersed on carbon (Au@Pt/C) and were used to catalyze methanol electrooxidation in acidic solutions at room temperature. The core-shell nanostructure was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy, and specific catalytic activities were evaluated by CO anodic stripping voltammetry in 0.5 M H(2)SO(4) and by cyclic voltammetry in 1 M CH(3)OH + 0.5 M H(2)SO(4). The Au@Pt/C catalyst demonstrated enhanced specific activity in methanol electrooxidation and showed multiple CO stripping peaks which were all negatively shifted with respect to a similarly prepared Ag@Pt/C catalyst. The activity enhancement is attributed to the presence of Au underneath a very thin Pt shell where electron exchange between Au and Pt had promoted the formation of active oxygen species on Pt, which facilitated the removal of inhibiting CO-like reaction intermediates.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Fabrication and catalytic properties of Pt and Ru decorated TiO2⧹CNTs catalyst for methanol electrooxidation

Highly ordered anodic titania nanotube arrays provide a large surface area for electrodepositing nickel nanoparticles which are used as the catalyst for carbon nanotube growth. Pt and Ru nanoparticles, approximately 3 nm in diameter, are uniformly electrodeposited on the as synthesized titania-supported carbon nanotubes (CNTs), constructing a novel catalyst for electrocatalytic oxidation of methanol. An enhanced and stable catalytic activity is obtained due to the uniformly dispersed Pt and Ru nanoparticles, and the large CNT network facilitating the electron transfer between the adsorbed methanol molecules and the catalyst substrate. An oxidation peak current density of 55 mA/cm² is achieved at a low Pt load of 0.126 mg/cm² with a Pt/Ru mole ratio of 1:1.