Electrocatalytic activity of Pd nanoparticles supported on poly(3,4-ethylenedioxythiophene)-graphene hybrid for ethanol electrooxidation

The support materials play a critical role for the electrocatalytic oxidation of ethanol on precious metal catalysts in fuel cells. Here, we report the poly(3,4-ethylenedioxythiophene) combined with reduced graphene oxide (PEDOT-RGO) as the support of Pd nanoparticles (NPs) for ethanol electrooxidation in alkaline medium. The as-prepared Pd/PEDOT-RGO composite catalysts are characterized by Raman spectrometer, X-ray diffraction, transmission electron microcopy, and scanning electron microcopy. PEDOT-RGO composite with the porous structure facilitates the dispersion of Pd NPs with a smaller size leading to the increase of electrochemical active surface area. The electrochemical properties and electrocatalytic activities of Pd/PEDOT-RGO hybrid are evaluated by cyclic voltammetry, chronoamperometry, CO stripping voltammetry, electrochemical impedance spectroscopy (EIS) and Tafel analysis. The results suggest that Pd/PEDOT-RGO hybrid shows a higher electrocatalytic activity, a better long-term stability, and the poisoning tolerance for the ethanol electrooxidation than Pd on carbon black. EIS and Tafel analysis indicate that PEDOT-RGO improves the kinetics of ethanol electrooxidation on the Pd NPs and is an efficient support in fuel cells.     

Ordered PdCu‐Based Nanoparticles as Bifunctional Oxygen‐Reduction and Ethanol‐Oxidation Electrocatalysts

The development of superior non‐platinum electrocatalysts for enhancing the electrocatalytic activity and stability for the oxygen‐reduction reaction (ORR) and liquid fuel oxidation reaction is very important for the commercialization of fuel cells, but still a great challenge. Herein, we demonstrate a new colloidal chemistry technique for making structurally ordered PdCu‐based nanoparticles (NPs) with composition control from PdCu to PdCuNi and PtCuCo. Under the dual tuning on the composition and intermetallic phase, the ordered PdCuCo NPs exhibit better activity and much enhanced stability for ORR and ethanol‐oxidation reaction (EOR) than those of disordered PdCuM NPs, the commercial Pt/C and Pd/C catalysts. The density functional theory (DFT) calculations reveal that the improved ORR activity on the PdCuM NPs stems from the catalytically active hollow sites arising from the ligand effect and the compressive strain on the Pd surface owing to the smaller atomic size of Cu, Co, and Ni.     

Pt 纳米颗粒在聚二甲基二烯丙基氯化铵功能化碳纳米管上的自发沉积及其对甲醇的电氧化性能

利用聚二甲基二烯丙基氯化铵(PDDA)非共价修饰的碳纳米管(CNTs)与PtCl₆^2-之间的自发氧化还原作用, 制备了Pt 纳米颗粒(Pt NPs)/CNTs-PDDA复合催化剂. PDDA在该催化剂中具有三种作用: (1) 作为金属前驱体PtCl₆^2-还原为Pt NPs 的还原剂; (2) 作为原位产生的Pt NPs 的稳定剂; (3) 在CNTs 表面形成保护膜抑制CNTs 在甲醇电催化氧化过程中的腐蚀. 采用傅里叶变换红外(FTIR)光谱、热重分析和拉曼光谱对CNTs-PDDA进行了表征, 表明PDDA通过π-π作用已成功覆盖在CNTs 表面, 并且修饰过程没有导致CNTs 结构的破坏. 采用透射电子显微镜(TEM)对Pt NPs/CNTs-PDDA 催化剂进行了表征, 结果表明, Pt NPs 均匀地分散在CNTs上, 平均粒径约2 nm, 且粒径分布范围窄. 用循环伏安法、计时电流法进一步考察了Pt NPs/CNTs-PDDA催化剂在酸性介质中对甲醇的电催化氧化的性能. 电化学测试结果表明, 与原始CNTs 负载的Pt NPs催化剂相比,Pt NPs/CNTs-PDDA催化剂具有更高的电化学活性表面积、电催化质量比活性和稳定性.     

Three‐Dimensional Nitrogen‐Doped Reduced Graphene Oxide–Carbon Nanotubes Architecture Supporting Ultrafine Palladium Nanoparticles for Highly Efficient Methanol Electrooxidation

A three‐dimensional (3D) nitrogen‐doped reduced graphene oxide (rGO)–carbon nanotubes (CNTs) architecture supporting ultrafine Pd nanoparticles is prepared and used as a highly efficient electrocatalyst. Graphene oxide (GO) is first used as a surfactant to disperse pristine CNTs for electrochemical preparation of 3D rGO@CNTs, and subsequently one‐step electrodeposition of the stable colloidal GO–CNTs solution containing Na₂PdCl₄ affords rGO@CNTs‐supported Pd nanoparticles. Further thermal treatment of the Pd/rGO@CNTs hybrid with ammonia achieves not only in situ nitrogen‐doping of the rGO@CNTs support but also extraordinary size decrease of the Pd nanoparticles to below 2.0 nm. The resulting catalyst is characterized by scanning and transmission electron microscopy, X‐ray diffraction, Raman spectroscopy, and X‐ray photoelectron spectroscopy. Catalyst performance for the methanol oxidation reaction is tested through cyclic voltammetry and chronoamperometry techniques, which shows exceedingly high mass activity and superior durability.     

Efficient anchorage of Pd nanoparticles on carbon nanotubes as a catalyst for hydrazine oxidation

A simple method is devised to deposit well-dispersed Pd nanoparticles on multi-walled carbon nanotubes (CNTs). Pd nanoparticles (1–3 nm) prepared in ethanol were transferred to toluene solution and modified by organic molecule benzyl mercaptan which acts as a cross linker between Pd nanoparticles and CNTs. The morphology and structure of the resulting Pd/CNT nanocomposite were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Pd nanoparticles were highly dispersed and effectively anchored on CNTs. The excellent electrocatalytic activity of the Pd/CNT nanocomposite for the oxidation of hydrazine was demonstrated by cyclic voltammetry.     

Performance study of palladium modified platinum anode in direct ethanol fuel cells: A green power source

The direct ethanol fuel cell is a green and renewable power source alternative to fossil fuels and produces less emissions compared to a combustion engine. Ethanol can be generated in great quantity from renewable resources like biomass through a fermentation process. Bio-generated ethanol is thus attractive fuel since growing crops for biofuels absorbs much of the carbon dioxide emitted into the atmosphere from the oxidation of ethanol. The platinum and palladium were co-deposited on graphite substrate by the galvanostatic technique and employed as anode catalyst for ethanol electrooxidation. The information on surface morphology, structural characteristics and bulk composition of the catalyst was obtained using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy. The cyclic voltammetry (CV) were used for the estimation of the electrochemically active surface area (ECSA) of the synthesized catalysts in alkaline medium. The CVs for ethanol oxidation revealed superior catalytic activity of Pt–Pd/C compared to Pd/C and Pt/C. The effect of OH^? on ethanol oxidation at Pt–Pd/C catalyst was studied using cyclic voltammetry, quasisteady-state polarization, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The Pt–Pd/C catalyst shows good stability and enhanced electrocatalytic activity is ascribed to the synergistic effect of higher electrochemical surface area, preferred OH^? adsorption on the surface and palladium ad-atom contribution on the alloyed surface.     

Highly dispersed Pd nanoparticles on covalent functional MWNT surfaces for methanol oxidation in alkaline solution

4-Aminobenzoic acid (4-ABA) was covalently grafted on to the surface of multiwalled carbon nanotubes (MWNTs) via a novel amine-cation induced radical reaction. Then, Pd nanoparticles were deposited on functional 4-ABA group-grafted MWNTs (F-MWNTs) by NaBH₄ reduction method. The structure and nature of the resulting product were characterized by Fourier transform infrared (FT-IR) spectrometry, transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements. The electrocatalytic properties of the Pd/F-MWNTs catalyst for methanol oxidation have been investigated by cyclic voltammetry, linear sweep voltammetry and chronomperometry methods. In contrast to the unfunctionalized counterpart, the electrochemical results demonstrate that Pd/F-MWNTs exhibit better electrocatalytic activities and stability, mainly due to the uniform dispersion and small particle size of Pd nanoparticles on the F-MWNT supports. The results imply that the Pd/F-MWNTs catalyst shows the better electrocatalytic performances and has a promising application potential in fuel cells.     

Biosensor Based on Self‐Assembling Glucose Oxidase and Dendrimer‐Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

A novel amperometric glucose biosensor based on layer‐by‐layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer‐encapsulated Pt nanoparticles (Pt‐DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt‐DENs layer and an anionic GOx layer. Transmission electron microscopy images and ζ‐potentials proved the formation of layer‐by‐layer nanostructures on carboxyl‐functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt‐DENs toward H₂O₂ and special three‐dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5 μM, a wide linear range of 5 μM–0.65 mM, a short response time (within 5 s), and high sensitivity (30.64 μA mM^?1 cm^?2) and stability (80% remains after 30 days).     

High‐Efficiency Encapsulation of Pt Nanoparticles into the Channel of Carbon Nanotubes as an Enhanced Electrocatalyst for Methanol Oxidation

Pt‐based nanostructures serving as anode catalysts for the methanol oxidation reaction (MOR) have been widely studied for many years. Nevertheless, challenging issues such as poor reaction kinetics and the short‐term stability of the MOR are the main drawbacks of such catalysts and limit their applications. Herein, we have developed a facile approach to encapsulate Pt nanoparticles (NPs) inside the nanochannels of porous carbon nanotubes (CNTs; Pt‐in‐CNTs) as a new enhanced electrocatalytic material. The as‐prepared CNTs offer simultaneously ordered diffusion channels for ions and a confinement effect for the NPs, which both facilitate the promotion of catalytic kinetics and avoid the Ostwald ripening of Pt NPs, thus leading to high activity and durable cycle life as an anode catalyst for MOR. This work provides a new approach for enhancing the stability and activity by optimizing the structure of the catalyst, and the Pt‐in‐CNTs represent the most durable catalysts ever reported for MOR.     

DNA‐Directed Growth of Pd Nanocrystals on Carbon Nanotubes towards Efficient Oxygen Reduction Reactions

Unique DNA‐promoted Pd nanocrystals on carbon nanotubes (Pd/DNA–CNTs) are synthesized for the first time, in which through its regularly arranged PO₄^3? groups on the sugar–phosphate backbone, DNA directs the growth of ultrasmall Pd nanocrytals with an average size of 3.4 nm uniformly distributed on CNTs. The Pd/DNA–CNT catalyst shows much more efficient electrocatalytic activity towards oxygen reduction reaction (ORR) with a much more positive onset potential, higher catalytic current density and better stability than other Pd‐based catalysts including Pd nanocrystals on carbon nanotubes (Pd/CNTs) without the use of DNA and commercial Pd/C catalyst. In addition, the Pd/DNA–CNTs catalyst provides high methanol tolerance. The high electrocatalytic performance is mainly contributed by the ultrasmall Pd nanocrystal particles grown directed by DNA to enhance the mass transport rate and to improve the utilization of the Pd catalyst. This work may demonstrate a universal approach to fabricate other superior metal nanocrystal catalysts with DNA promotion for broad applications in energy systems and sensing devices.     

Mild Synthesis of Pt/SnO2/Graphene Nanocomposites with Remarkably Enhanced Ethanol Electro‐oxidation Activity and Durability

We have designed a new Pt/SnO₂/graphene nanomaterial by using L ‐arginine as a linker; this material shows the unique Pt‐around‐SnO₂ structure. The Sn²⁺ cations reduce graphene oxide (GO), leading to the in situ formation of SnO₂/graphene hybrids. L ‐Arginine is used as a linker and protector to induce the in situ growth of Pt nanoparticles (NPs) connected with SnO₂ NPs and impede the agglomeration of Pt NPs. The obtained Pt/SnO₂/graphene composites exhibit superior electrocatalytic activity and stability for the ethanol oxidation reaction as compared with the commercial Pt/C catalyst owing to the close‐connected structure between the Pt NPs and SnO₂ NPs. This work should have a great impact on the rational design of future metal–metal oxide nanostructures with high catalytic activity and stability for fuel cell systems.     

Pd‐Cu alloy nanoparticle supported on amine‐terminated ionic liquid functional 3D graphene and its application on Suzuki cross‐coupling reaction

Well distributed Pd‐Cu bimetallic alloy nanoparticles supported on amine‐terminated ionic liquid functional three‐dimensional graphene (3D IL‐rGO/Pd‐Cu) as an efficient catalyst for Suzuki cross‐coupling reaction has been prepared via a facile synthetic method. The introduction of IL‐NH₂ cations on the surface of graphene sheets can effectively avoid the re‐deposition of graphene sheets, allowing the catalyst to be reused up to 10 cycles. The addition of Cu not only saves cost but also ensures high catalytic efficiency. It is worthy to note that the catalyst 3D IL‐rGO/Pd_2.5Cu_2.5 can efficiently catalyze the Suzuki cross‐coupling reaction with the yield up to 100% in 0.25 h, almost one‐fold higher than that by the pristine IL‐rGO/Pd_2.5 catalyst (52%). The Powder X‐Ray Diffraction (XRD), combining energy dispersive X‐ray spectroscopy (EDS) mapping results confirm the existence and distribution of Pd and Cu in the bimetallic nanoparticles. The transmission electron microscopy (TEM) reveals the nanoparticle size with an average diameter of 3.0 ± 0.5 nm. X‐ray photoelectron spectroscopy (XPS) analysis proved the presence of electron transfer from Cu to Pd upon alloying. Such alloying‐induced electronic modification of Pd‐Cu alloy and 3D ionic liquid functional graphene with large specific surface area both accounted for the catalytic enhancement.     

Microwave Irradiation for the Facile Synthesis of Transition‐Metal Nanoparticles (NPs) in Ionic Liquids (ILs) from Metal–Carbonyl Precursors and Ru‐, Rh‐, and Ir‐NP/IL Dispersions as Biphasic Liquid–Liquid Hydrogenation Nanocatalysts for Cyclohexene

Stable chromium, molybdenum, tungsten, manganese, rhenium, ruthenium, osmium, cobalt, rhodium, and iridium metal nanoparticles (M‐NPs) have been reproducibly obtained by facile, rapid (3 min), and energy‐saving 10 W microwave irradiation (MWI) under an argon atmosphere from their metal–carbonyl precursors [M_x(CO)_y] in the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIm][BF₄]). This MWI synthesis is compared to UV‐photolytic (1000 W, 15 min) or conventional thermal decomposition (180–250 °C, 6–12 h) of [M_x(CO)_y] in ILs. The MWI‐obtained nanoparticles have a very small (<5 nm) and uniform size and are prepared without any additional stabilizers or capping molecules as long‐term stable M‐NP/IL dispersions (characterization by transmission electron microscopy (TEM), transmission electron diffraction (TED), and dynamic light scattering (DLS)). The ruthenium, rhodium, or iridium nanoparticle/IL dispersions are highly active and easily recyclable catalysts for the biphasic liquid–liquid hydrogenation of cyclohexene to cyclohexane with activities of up to 522 (mol product) (mol Ru)^?1 h^?1 and 884 (mol product) (mol Rh)^?1 h^?1 and give almost quantitative conversion within 2 h at 10 bar H₂ and 90 °C. Catalyst poisoning experiments with CS₂ (0.05 equiv per Ru) suggest a heterogeneous surface catalysis of Ru‐NPs.     

Triazine-based polymers as nanostructured supports for the liquid-phase oxidation of alcohols

A covalent triazine framework (CTF) was used as support for palladium nanoparticles (NPs) and Pd/CTF was applied as the catalyst in the selective oxidation of benzyl alcohol. N groups in the CTF appeared more efficient than those created on carbon nanotubes (CNTs) by NH₃/high‐temperature treatment in stabilizing Pd NPs against growth during the immobilization step. This assured a high metal dispersion, which led to a highly active and stable catalyst in the alcohol oxidation reaction. Indeed, Pd on the CTF was more stable in recycling than Pd on activated carbon (AC) and on nitrogen‐doped CNTs, particularly avoiding leaching of Pd NPs. Moreover, Pd on the CTF was less sensitive than Pd on AC to the decrease of reactant concentration. This in turn led to a higher selectivity to benzaldehyde (98 %) with a considerable activity (turnover frequency 1453 h^?1).     

MWCNTs/Ionic Liquid/Graphene Quantum Dots Nanocomposite Coated with Nickel‐Cobalt Bimetallic Catalyst as a Highly Selective Non‐enzymatic Sensor for Determination of Glucose

In this work, a glassy carbon electrode (GCE) was modified with multiwall carbon nanotubes/ionic liquid/graphene quantum dots (MWCNTs/IL/GQDs) nanocomposite. Then, the nanocomposite was decorated with nickel‐cobalt nanoparticles (Ni?Co NPs), and it was used as a non‐enzymatic glucose sensor. Field emission scanning electron microscopy, X‐ray diffraction spectroscopy, and energy dispersive spectroscopy were employed to prove the electrodeposition of the Ni?Co NPs on the surface of MWCNTs/IL/GQDs/GCE. Also, cyclic voltammetric and amperometric methods were utilized for the investigation of the electrochemical behaviour of the Ni?Co NPs/MWCNTs/IL/GQDs/GCE for glucose oxidation. The novel amperometric sensor displayed two linear ranges from 1.0 to 190.0 μmol L^?1 and 190.0 to 4910 μmol L^?1 with a low detection limit of 0.3 μmol L^?1 as well as fast response time (2 s) and high stability. Also, the sensor showed good selectivity for glucose determination in the presence of ascorbic acid, citric acid, dopamine, uric acid, fructose, and sucrose, as potential interference species. Finally, the performance of the proposed sensor was investigated for the glucose determination in real samples. Ni?Co NPs/MWCNTs/IL/GQDs/GCE showed good sensitivity and excellent selectivity.     

Bimetallic palladium–gold nanoparticles synthesized in ionic liquid microemulsion

The palladium and gold precursors were dissolved in dispersive and continuous phase of ionic liquid microemulsion (H₂O/Triton X-100 (TX-100)/1-butyl-3-methylimidazolium hexafluorophosphate), respectively. [PdCl₆]^2? ions were reduced in situ by TX-100 in dispersive phase (H₂O) to prepare Pd nanoparticles (NPs) and then [AuCl₄]^? crossed through the interface film and reacted with the as-prepared Pd NPs to form Pd₄Au NPs. The as-prepared Pd₄Au NPs were characterized by transmission electronic microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy. The as-prepared Pd₄Au NPs suspension and carbon nanotubes (CNTs) suspension were vigorously stirred to prepare the electrocatalyst supported on the CNTs with a total metal loading of 20?wt.% (denoted by Pd₄Au/CNTs). Cyclic voltammetry and chronoamperometry tests show that the Pd₄Au/CNTs are very promising for the oxidation of ethanol in alkaline medium. The result can be attributed to the synergistic effect between Pd and Au during the catalytic process.     

功能化碳纳米管表面高分散的钯纳米粒子在碱性溶液中的甲醇氧化行为

本工作中在水溶液体系中以芳烃重氮盐修饰的多壁碳纳米管(MWNT)为载体构筑了钯(Pd)纳米粒子碳纳米管复合结构。以MWNT的侧壁上C-C共价键接的氨基苯甲酸为沉积活化中心,制备了高分散高催化活性的钯(Pd)纳米粒子。结构成分和形貌分别用XRD和TEM表征。循环伏安(CV) 和交流阻抗的研究表明上述复合结构在碱性溶液中对甲醇的电催化氧化有很高的活性及稳定性。芳烃重氮盐修饰的MWNT是一种非常好的催化剂载体,而Pd-MWNT复合材料在燃料电池有着广泛的应用前景。     

One‐Pot Synthesis of Carbon‐Supported Dendritic Pd‐Au Nanoalloys for Electrocatalytic Ethanol Oxidation

One‐pot synthesis of carbon‐supported Pd‐Au alloy nanoparticles with well‐defined dendritic shape (Pd‐Au_den/C) was achieved by co‐reduction of K₂PdCl₄/HAuCl₄ mixtures in a molar ratio of 1:1 with hydrazine in the presence of Vulcan XC‐72R. The prepared Pd‐Au_den/C exhibited significantly enhanced performance in the electrocatalytic oxidation of ethanol compared with dendritic Pd nanoparticles and a commercial Pd/C catalyst. Pd‐Au_den/C even showed higher durability in electro‐oxidation of ethanol than the supported catalyst prepared by the deposition of presynthesized dendritic Pd‐Au nanoparticles on the carbon support. The experimental results clearly indicate that enhanced interaction between nanoparticle catalysts and carbon support through the one‐pot synthesis protocol can improve the durability of the electrocatalysts.     

Synthesis of Pd-Based Bimetallic Nanoparticles and Their Effective Electrocatalytic Properties

In this work, we developed a simple and effective one-pot method to synthesize the Pd-based bimetallic nanoparticles (NPs) in the presence of polyvinylpyrrolidone (PVP). By using high-resolution transmission electron microscopy (HRTEM), energy-dispersive spectrometry (EDS) mapping and X-ray diffraction (XRD), the morphologies and compositions of the as-prepared bimetallic NPs were investigated in detail. Furthermore, this approach was also used to achieve the highly dispersive Pd-based bimetallic NPs directly on the carbon black. Significantly, the as-obtained carbon-supported Pd-based bimetallic NPs showed excellent electrocatalytic activity for the methanol oxidation. Among the Pd-based bimetallic NPs and the commercial Pd–C, the PdPt–C displayed the best electrocatalytic activity and stability, which may be mainly attributed to the specific nanostructure and the synergetic effect between Pt and Pd atoms.

     

Electroanalytical Determination of Paracetamol Using Pd Nanoparticles Deposited on Carboxylated Graphene Oxide Modified Glassy Carbon Electrode

The study presents a novel paracetamol (PA) sensor based on Pd nanoparticles (PdNPs) deposited on carboxylated graphene oxide (GO?COOH) and nafion (Nf) modified glassy carbon electrode (GCE). The morphologies of the as prepared composites were characterized using high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FTIR). The experimental results demonstrated that Nf/GO?COOPd displayed excellent electrocatalytic response to the oxidation PA. The linear range was 0.04–800 μM for PA with limit of detection of 0.012 μM and excellent sensitivity of 232.89 μA mM^?1 cm^?2. By considering the excellent performance of Nf/GO?COOPd composite such as wider linear range, lower detection, better selectivity, repeatability, reproducibility, and storage stability, the prepared composite, especially GO?COOH support, with satisfactory electrocatalytic properties was a promising material for the modification of electrode material in electrochemical sensor and biosensor field.