Effects of Carbonization Temperature and Time during Carbon Riveting Process on the Stability of Pt/C Catalyst

Effects of carbonization temperature and time during carbon riveting process on the stability of Pt/C catalysts have been investigated systematically. X‐ray diffraction, transmission electron microscopy, cyclic voltammograms, and accelerated potential cycling tests have been performed to characterize the catalysts. The experimental results show that the activity of the riveted Pt/C catalyst decreases with the increasing of the heat‐treated temperature and the extension of heat‐treated time due to sintering of Pt nanoparticles. The stability of the carbon riveted Pt/C catalysts exhibits the increasing trend with the increase of the carbonization time and temperature. Considering both of the activity and stability of the riveted Pt/C catalysts, the optimized carbonization temperature and time are 400 °C and 60 min for a Pt/VulcanXC‐72 catalyst with starting particle size before carbonization of 2.2 nm and 20 wt% platinum loading, respectively.     

氮掺杂碳纳米材料在氧还原反应催化剂中的研究进展

长期以来,碳材料负载高分散的铂催化剂及其合金材料一直是商业化质子交换膜燃料电池（PEMFC）中氧还原反应和氢氧化反应十分有效的催化剂。但由于Pt基催化剂成本高、电化学条件下稳定性差、易CO中毒以及氧还原反应（ORR）动力学迟缓等一系列问题,阻碍了其在燃料电池中的进一步应用和大规模生产。相比之下,氮掺杂碳纳米材料具有低成本、高活性、高稳定性、环境友好等特点,这些优异的性能使其在燃料电池领域有着广阔的应用前景。结合近几年国内外研究现状,综述了原位掺杂法、后掺杂合成法和直接热解法等3种氮掺杂碳纳米材料的制备方法,并分析了各自的优点和不足之处,及其作为ORR催化剂的研究进展。最后,对未来氮掺杂碳纳米材料催化剂研究的主要发展方向进行了展望。     

Highly active palladium nanoparticles immobilized on knitting microporous organic polymers as efficient catalysts for Suzuki–Miyaura cross-coupling reaction

By encaging the Pd nanoparticles in the interior space of the hypercrosslinked microporous organic polymer, we successfully prepared a novel eco-friendly heterogeneous catalyst for Suzuki cross-coupling reaction. The catalyst afforded fast conversions for the Suzuki cross-coupling reaction even at a loading of 0.05 mmol% Pd, and the turnover frequency for the reaction could be up to 61,353 h^?1. Furthermore, this catalyst is stable enough to be reused more than five times with no appreciable activity decrease. This work provides a method for fabricating highly active microporous organic polymer encapsulated Pd catalysts for Suzuki cross-coupling reaction and resolve the problem of industrialization in traditional active carbon catalysts.     

Preparation of a Sulfonated Porous Carbon Catalyst with High Specific Surface Area

A sulfonated (SO₃H-bearing) carbon catalyst with mesoporous structure and high specific surface area is successfully prepared by impregnating the cellulosic precursor (wood powder) with ZnCl₂ prior to activation and sulfonation. The specific surface area of the porous carbon catalyst thus prepared is also found to increase with carbonization temperature to a maximum of 1,560 m² g^?1 at ca. 773 K. Structural analyses reveal that the porous carbon catalysts carbonized at temperatures higher than 723 K contain high densities of micro- and mesopores. The porous carbon catalyst exhibits high catalytic performance for the esterification of acetic acid (343 K), the activity for which is dependent only on the acid density. The porous carbon catalyst also exhibits high catalytic activity for the benzylation of toluene, whereas non-porous sulfonated carbon has very limited activity for this reaction. The activity for the benzylation of toluene is dependent on both the specific surface area and the acid density of the sulfonated porous carbon catalyst.     

钌炭催化剂的制备及其在芳环加氢反应中的应用

芳环加氢反应是最重要的合成反应之一,钌炭催化剂在芳环加氢反应中具有优异的催化性能。综述钌炭催化剂的制备方法和载体性质对钌炭催化剂的影响以及钌炭催化剂在苯、苯甲酸和对苯二甲酸二甲酯等芳环加氢反应中的应用进展。负载型钌炭催化剂的制备方法主要有浸渍法、沉淀法和升华法,超声辅助浸渍法可将大部分钌纳米粒子引入到炭载体的孔道内部,得到限域型负载钌炭催化剂。而镶嵌式钌炭催化剂主要是指通过原位炭化的方法将钌粒子部分镶嵌在炭的孔壁上,一步得到钌炭催化剂,其制备方法主要有软模板剂法和硬模板剂法。除制备方法外,炭的骨架结构、表面性质及氮掺杂对钌炭催化剂的性能影响也较大。镶嵌式钌炭催化剂具有钌纳米粒子和炭载体之间的相互作用强、催化剂抗流失及烧结性能好,在芳环加氢反应中表现出卓越的催化性能和稳定性。随着新制备技术的出现,新型镶嵌式钌炭催化剂将可能实现产业化。     

Preparation and Characterization of Pt/C and Pt/TiO2 Electrocatalysts by Liquid Phase Photodeposition

The preparation of carbon and titanium dioxide supported Pt catalysts through a photochemical and photocatalytic routes were investigated. The catalysts were prepared by irradiation with UV-light (365 nm) at room temperature using H₂PtCl₆ and C₁₀H₁₄O₄Pt (Pt(acac)₂) as platinum precursors. The kinetic studies revealed that H₂PtCl₆ produced metallic platinum faster than Pt(acac)₂ and also showed that the amount of platinum deposited on TiO₂ was higher than on carbon. The samples were characterized by X-ray diffraction, SEM/EDS and cyclic voltammetry. X-ray diffraction permitted to identify the crystallographic (111) and (200) planes from platinum metal on the catalysts synthesized, the intensity of peaks depends of the amount of platinum deposited. SEM/EDS test confirmed what it was found by the kinetics studies. The electrocatalytic activity was compared with a commercial Pt E-Tek catalyst (10 wt%). The electrochemical results showed that Pt/C-AA catalyst synthesized by liquid phase photo-deposition method has stability in acid media and high distribution of the actives sites on the electrode surfaces. It could be considered as a candidate for electro-catalyst for polymer electrolyte fuel cell. The Pt/TiO₂ catalysts did not present electrochemical activity.     

The role of Fe species in the pyrolysis of Fe phthalocyanine and phenolic resin for preparation of carbon-based cathode catalysts

Pyrolysis of a mixture of Fe phthalocyanine and phenolic resin (FePc/PhRs) was studied to clarify the details of the preparation protocol of nitrogen-doped carbon-based materials for cathode catalysts in polymer electrolyte membrane fuel cells. TEM images show that nanoshell carbon is formed by the pyrolysis of FePc/PhRs in the temperature range of 600-800 °C. The optimum pyrolysis temperature for the FePc/PhRs mixture was 600 °C, where moderate conductivity and high nitrogen content of the prepared carbon were both satisfied. This catalyst showed a promising fuel cell performance with 1.01 V open-circuit voltage and 0.33 W cm⁻² maximum output, at 0.2 MPa absolute pressure and 80 °C. A detailed study of the carbonization process suggests that the presence of Fe species during carbonization process contributes to higher nitrogen content and growth of nanoshell structure of the resulting carbon.     

Highly dispersed platinum-carbon aerogel catalyst for polymer electrolyte membrane fuel cells

Platinum loaded carbon aerogel catalysts for application in polymer electrolyte membrane fuel cells have been synthesized from the alcoholic sol-gel reaction of phloroglucinol with furfural using propylene oxide as a reducing agent of platinum salt, followed by supercritical drying with carbon dioxide. Subsequent carbonization of the platinum-organic aerogels under a reducing gas flow produced platinum-carbon aerogels. X-ray diffraction and transmission electron microscopy analyses of the platinum-carbon aerogel catalysts indicate the formation of well-dispersed platinum nanoparticles having sizes of about 3 nm. Surface characterization of the platinum-carbon aerogel by X-ray photoelectron spectroscopy reveals that 60% of the platinum is present in its metallic state. Electrochemical characterization by hydrogen adsorption/desorption cyclic voltammetry and CO stripping voltammetry indicates that the electrochemical active surface areas of the platinum-carbon aerogel are comparable to those of commercial catalysts.     

Screening of PdM and PtM catalysts in a multi-anode direct formic acid fuel cell

Direct formic acid fuel cells (DFAFC) currently employ either Pt-based or Pd-based anode catalysts for oxidation of formic acid. However, improvements are needed in either the activity of Pt-based catalysts or the stability of Pd-based catalysts. In this study, a number of carbon-supported Pt-based and Pd-based catalysts, were prepared by co-depositing PdM (M = Bi, Mo, or V) on Vulcan^® XC-72 carbon black, or depositing another metal (Pb or Sn) on a Pt/C catalyst. These catalysts were systematically evaluated and compared with commercial Pd/C, PtRu/C, and Pt/C catalysts in a multi-anode DFAFC. The PtPb/C and PtSn/C catalysts were found to show significantly higher activities than the commercial Pt/C catalyst, while the PdBi/C provided higher stability than the commercial Pd/C catalyst.     

质子交换膜燃料电池非铂电催化剂研究进展

质子交换膜燃料电池(PEMFCs)目前主要催化剂为贵金属Pt基催化剂。然而,Pt价格高、储量低等问题严重阻碍了PEMFCs的商业化进程。发展低成本、高性能的氧还原催化剂是解决铂资源短缺、降低燃料电池成本、实现燃料电池商业化的关键。结合本课题组的研究工作,综述了最近几年非铂催化剂在燃料电池阴极氧还原方面的研究进展,着重探讨了新型氮掺杂碳基纳米材料的设计与制备,并概述了非铂催化剂面临的困难以及未来发展方向。     

Enhanced methanol electro-oxidation activity of PtRu catalysts supported on heteroatom-doped carbon

A typical heteroatom (nitrogen)-doped carbon materials were successfully synthesized through the carbonization of a hybrid containing traditional carbon black covered by in situ polymerized polyaniline. The nitrogen content onto carbon can be adjusted up to 5.1 at.% by changing the coverage of polyaniline. The effects of nitrogen doping on the surface physical and electrochemical properties of carbon were studied using XPS, XRD and HRTEM, as well as CV and EIS techniques. With increasing nitrogen doping, the carbon structure became more compact, showing curvatures and dislocations in the graphene stacking. The nitrogen-doped carbon also exhibited a higher accessible surface area in electrochemical reactions, and a lower charge transfer resistance at the carbon/electrolyte interface. Moreover, to investigate the influence of nitrogen doping on the electrocatalytic activity of the PtRu/C catalyst, comparisons in CO stripping and methanol oxidation were carried out on PtRu catalysts supported by non-doped and nitrogen-doped carbon. Since the promotional roles of nitrogen doping, including the high electrochemically accessible surface area, the richness of the disordered nanostructures and defects, and the high electron density on N-doped carbon supports, contribute to the synthesis of well-dispersed PtRu particles with high Pt utilization and stronger metal-support interactions, an enhanced catalytic activity for methanol oxidation was obtained in the case of the PtRu/N-C catalyst in comparison with the traditional PtRu/C catalyst.     

Analysis of forming process of nitrogen-doped carbon catalyst derived from Fe 1,10-phenanthroline compound and its oxygen reduction reaction activity

The pyrolysis behavior of iron 1,10-phenanthroline compound, the change of crystalline structure of iron in the iron 1,10-phenanthroline compound, and nitrogen chemical state of nitrogen doped carbon catalyst derived from iron 1,10-phenanthroline compound were investigated to clarify the process of improvement of oxygen reduction reaction (ORR) activity on nitrogen-doped carbon catalyst by TGA, EGA-MS, HT-XRD, XRD, and XPS technique. The ORR activity drastically improved at a synthesis temperature of 700 °C, and was the highest at a synthesis temperature of 800 °C. But the ORR activity significantly dropped at a synthesis temperature of 900 °C. This low ORR activity of NC-900 is probably due to the increase of quaternary nitrogen ratio with progression of excessive carbonization, and the quaternary nitrogen to pyridine-like nitrogen ratio might be an important factor for improvement of the ORR activity.     

The construction of nitrogen-doped graphitized carbon–TiO2 composite to improve the electrocatalyst for methanol oxidation

The exploration of advanced catalyst supports is a promising route to obtain electrocatalysts with high activity and durability. Herein, the nitrogen-doped graphitized carbon/TiO₂ composite was fabricated and explored as support for the Pt catalyst. The composite support was constructed by carbonization of polypyrrole/TiO₂ using cobalt nitrate and nickel nitrate as graphitizing catalysts. The resulting catalyst shows enhanced electrocatalytic performance for methanol electrooxidation compared with the commercial Pt/C catalyst. The enhancement can be ascribed to combinatory effect of N-doped graphitized carbon and TiO₂, in which the tolerance to CO-poisoning and the intrinsic kinetics of methanol oxidation reaction were simultaneously improved by the bifunctional effect and the modification of the electronic structure. As a result, the as-developed nitrogen-doped graphitized carbon/TiO₂ composite present attractive advantages for the application in fuel cell electrocatalyst.     

Solid state NMR study of chemical structure and hydrothermal deactivation of moderate-temperature carbon materials with acidic SO3H sites

Hydrothermal stability of carbon based acid catalysts synthesized by sulfonating carbohydrates pyrolyzed at moderate temperatures (300–600 °C) has been reported previously. To test the effect of carbon structure on hydrothermal stability, we produced catalysts by dry pyrolysis at 350 °C and 450 °C or by hydrothermal carbonization, followed by sulfonation with fuming sulfuric acid, as well as by direct sulfonation of glucose. The catalysts were characterized by BET, titration, Raman spectroscopy, TGA, XPS, reaction testing, and ¹³C solid state NMR. Catalysts were hydrothermally treated and then analyzed for sulfur retention and catalytic activity. The lower temperature carbon catalysts showed the best stability, however all showed significant activity loss. Solid state NMR of materials made from ¹³C-glucose was used to characterize the structural details in an attempt to correlate functional groups to hydrothermal stability of catalyst active sites. Structural models generated from NMR data showed that the most stable catalysts contained a significant fraction of furan rings and hardly any polycondensed aromatic rings.     

Functionalized carbon support with sulfonated polymer for direct methanol fuel cells

Recently electrodes for direct methanol fuel cell (DMFC) have been developed for getting high fuel cell performances by controlling composition of catalysts and sulfonated polymers, developing catalyst particles, modifying carbon supports, etc. The electrodes in DMFCs are porous layers, which are composed of catalyst, which is black or carbon supported, and sulfonated polymers in a blended form. In the present study, carbon support for catalysts was functionalized to play dual roles of a mass transport and a catalyst support. The functionalized carbon support was characterized and compared with pristine one by thermal and spectroscopic analysis, and loading of platinum (Pt) catalysts on modified support was performed by gas reduction. The electrodes with Pt on functionalized carbon support were fabricated, though the conventional electrodes were prepared with sulfonated polymer and Pt catalysts. Membrane electrode assembly with Pt catalyst on functionalized support showed a higher DMFC performance of 30 mW cm⁻² at 50 °C without using additional sulfonated polymer. Integration of electrode components in one body has another advantage of easier and simpler process in preparing electrodes for DMFCs. Improved DMFC performance of the electrode containing functionalized carbon was be attributed to a better mass transport which maximize the catalytic activities.     

Hierarchical porous nitrogen-doped carbon materials derived from one-step carbonization of polyimide for efficient CO<Subscript>2</Subscript> adsorption and separation

Hierarchical porous nitrogen-doped carbon (HPNC) materials are synthesized through one-step carbonization of polyimide using triblock copolymer P123 as mesoporous template. The microstructure, chemical composition and CO₂ adsorption behaviors are investigated in detail. The results show that HPNC materials have hierarchical micro-/mesopore structures, high specific surface area of 579 m²/g, large pore volume of 0.34 cm³/g, and nitrogen functional groups (5.2 %). HPNC materials exhibit high CO₂ uptake of 5.56 mmol/g at 25 °C and 1 bar, which is higher than those of previously reported nitrogen-doped porous carbon materials. After 5 cycles the value of CO₂ adsorption uptakes is 5.28 mmol/g, which is approximately 95 % of the original adsorption capacity. The estimated CO₂/N₂ selectivity of HPNC materials is 17, revealing great promise for practical CO₂ adsorption and separation applications. The efficient CO₂ uptake and enhanced CO₂/N₂ selectivity are due to the combination of nitrogen-doped and hierarchical porous structures of HPNC materials.     

掺氮碳基材料在费托合成反应中的应用

氮掺杂是一种对碳材料结构和性质进行修饰的重要方法。本文主要介绍了碳基材料掺氮的主要方法(即直接合成法和后处理法)及所得掺氮碳基材料的性质。重点综述了近年来掺氮碳基材料在制备费托合成钴基和铁基催化剂领域中的应用,进一步阐述了掺氮碳基材料作为新型费托合成催化剂载体所具有的主要优点:载体表面含氮基团具有锚定作用可提高金属活性组分分散度,同时,氮的掺杂不仅能够有效地提高催化剂还原度,而且富电子的氮物种可促进CO解离,从而有利于提高催化剂费托合成反应性能。在此基础上,本文也分析了掺氮碳基材料的合成和催化应用方面所存在的问题。     

Platinum embedded within carbon nanospheres for shape selective liquid phase hydrogenation

Reactant shape selective catalysis occurs when substrates of different sizes and shapes are consumed at different rates over catalysts that combine molecular sieving transport processes with reaction. By contrast the same substrates react at nearly equivalent rates over catalysts that have large, open pores that do not induce any form of molecular sieving. Here we describe the design and synthesis of reactant shape selective catalysts for liquid phase hydrogenation reactions. Using an emulsion polymerization of furfuryl alcohol, we have made catalysts that consist of microporous carbon nanospheres within which are embedded platinum nanoparticles. The porosity of the carbon spheres was found to be a key parameter affecting catalyst activity and selectivity; porosity was varied by adding pore forming agents, such as polyethylene glycol with different molecular weights, during synthesis, or by mild oxidation of the as-synthesized catalyst using carbon dioxide. In addition to increasing porosity to reduce mass transfer limitations, a synthesis of smaller carbon spheres (<200 nm) was devised to reduce the micropore diffusion length. Decreasing the particle size of the catalyst by adjusting the surfactant composition during polymerization, improved the effectiveness factor by approximately one order of magnitude making it as active as a comparable standard metal catalyst.     

A Review on Metal‐Free Doped Carbon Materials Used as Oxygen Reduction Catalysts in Solid Electrolyte Proton Exchange Fuel Cells

Within the last decade, metal‐free heteroatom doped carbon nanomaterials have gained attention as effective electrocatalysts for the oxygen reduction reaction (ORR) in many electrochemical systems. Since then, reports have stated that the ORR catalytic activity, onset potential, and H₂O production selectivity of these materials is similar to that of platinum‐based catalysts. These statements rely on cyclic voltammetry (CV) and rotating disc electrode (RDE) measurements in liquid alkaline electrolyte. However, fuel cell researchers aim to replace the costly platinum catalysts in the more prominent acidic solid electrolyte proton exchange fuel cell (PEFC). In this respect, there are only a few reports of unpromising activity, stability, and H₂O production selectivity. In addition, only few reports have been presented on the implementation of such materials in cathode catalyst layers of actual PEFC devices. This mini‐review aims to summarize and evaluate results of these reports. Material synthesis, cell power, open circuit voltage, stability properties, and proposed active sites are reviewed. To date, the highest reported PEFC power densities with guaranteed metal‐free heteroatom doped carbon cathode catalysts have reached up to 321 mW cm⁻²; which although a promising value is substantially short of values obtained for platinum based catalysts.     

One-pot hydrothermal synthesis of nitrogen-doped hierarchically porous carbon monoliths for supercapacitors

The nitrogen-doped hierarchically porous carbon monoliths (N-HPCMs) were successfully synthesized by using dicyandiamide (DCDA) as nitrogen source, phenolic resol as carbon precursor and mixed triblock copolymers as templates via a one-pot hydrothermal approach. The obtained carbon monoliths possess tunable mesopore size (4.3–11.4 nm), large surface area (552–660 m²/g), and high nitrogen content (up to 12.1 wt%). Ascribed to the nitrogen-doped frameworks and hierarchical porosity, N-HPCMs exhibit good electrochemical performance as the supercapacitor electrode with specific capacitance of 268.9 F/g (in 6 M KOH) at a current density of 1 A/g, and a 4.1 % loss of the specific capacitance after 5,000 charge–discharge cycles, indicating a long-term cycling stability. Such unique features make N-HPCMs promising electrode materials for high performance supercapacitors.