Non-noble metal catalyst on carbon ribbon for fuel cell cathode

A non-noble metal Fe/N/C catalyst is prepared by pyrolyzing the ball-milled mixture of graphitized carbon ribbon, iron precursor, and nitrogen precursor in ammonia. The Fe/N/C catalyst shows high ORR activity in alkaline solution, together with much improved stability compared with Pt/C catalyst. In the catalyst, FeN particles are covered by graphitic carbon layers. The activity is proposed to originate from the FeN and Fe/N/C sites. The stability is explained by the protecting effect of the carbon layers surrounding the FeN particles. The ORR mechanism on the Fe/N/C catalyst is proposed to be similar with Pt/C catalyst based on the Tafel plots. The Fe/N/C catalyst shows great potential in ORR in alkaline solution, while the performance in acid still needs improvement.     

微波-胶体法制备PEMFC纳米Pt/C电催化剂

质子交换膜燃料电池(PEMFC)，具有高功率密度、高能量转换效率、低工作温度和环境友好的优点，被认为是第五代燃料电池和未来较为理想的电动汽车动力源之一。为了降低PEMFC中氧还原反应的电化学极化，提高电池的输出功率，目前普遍采用Pt作为催化剂。Pt资源匮乏，价格昂贵，研究开发更好的制备工艺以减小Pt金属尺     

Mesoporous platinum as sulfur-tolerant catalyst for PEMFC cathodes

The performance of proton exchange membrane fuel cell (PEMFC) is highly influenced by its operating conditions. One of the vital parameter is the purity of feed gases. The cathode of PEMFC is normally fed with air from the atmosphere containing certain impurities like CO₂, NO₂, and SO₂, which are the major contaminants for the electrocatalysts used in the fuel cell, causing both reversible and irreversible damages. The irreversible effect is caused due to adsorption of impurities like SO₂ on the conventionally used platinum catalyst supported on carbon (Pt/C). It has been observed that carbon facilitates the absorption of SO₂ on platinum. Hence, the present objective is to identify the catalysts containing no carbon and study their impurity tolerance in the fuel cell environment. In the present paper, we have attempted to synthesize unsupported mesoporous platinum by hard template method and studied its SO₂ impurity tolerance at the cathode side for oxygen reduction reaction (ORR) for PEMFC application. The mesoporous platinum showed for a higher tolerance towards SO₂ compared to its counterpart, viz., platinum black. Sulfur tolerance was evaluated by the sulfur coverage on the catalyst and its rate of recovery through electrochemical experiments. Mesoporous platinum has also exhibited a faster removal of adsorbed sulfur compared to the commercial microporous platinum black, revealing that the recovery is also fast comparatively for meso-structured platinum.

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Graphical abstract Morphology and cyclic voltammogram of mesoporous platinum (inset: sulfur coverage for mesoporous platinum and platinum black)

     

Non-noble metal Bi/BiVO4 photoanode for surface plasmon resonance-induced photoelectrochemical biosensor of hydrogen peroxide detection

Non-noble metal for surface plasmon resonance (SPR)-induced nano-enzymatic photoelectrochemical (PEC) biosensors is a promising method for broad applications. Non-noble metal bismuth (Bi) is gradually being valued for their properties such as non-toxicity, abundant reserves, and good catalysis. Meanwhile, metallic Bi nanoparticles (NPs) have superior SPR properties similar to that of noble metal. Therefore, a non-noble metal Bi/BiVO₄ photoanode based on SPR was designed for the PEC detection of H₂O₂ in this work. The synergistic effect of BiVO₄ with suitable band gap (2.5 eV) and Bi NPs with superior SPR effectively reduces the recombination of photogenerated electrons and holes, which significantly improves the PEC activity of Bi/BiVO₄ electrode at low voltage. The in situ Bi/BiVO₄/FTO photoelectrode not only exhibits a more comprehensive linear range of 0.005–2.6 mM with a lower detection limit of 2.0 μM but also possesses excellent selectivity for the determination of H₂O₂ because the coexisting substances are difficult to be oxidized at 0 V bias voltage. The investigation of Bi/BiVO₄-based sensor has contributed to the development of non-noble metal for SPR-induced PEC biosensors.

     

Pt4ZrO2/C cathode catalyst for improved durability in high temperature PEMFC based on H3PO4 doped PBI

In this paper, Pt₄ZrO₂/C was prepared and compared with commercial Pt/C (46.6 wt.% TKK) in terms of the durability as cathode catalyst in a high temperature proton exchange membrane fuel cell (PEMFC) based on H₃PO₄ doped polybenzimidazole (PBI) by a potential sweep test. The catalysts before and after the potential sweep test were characterized by rotating disk electrode (RDE), X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). After 3000 cycles potential sweep test, the overall performance loss of the Pt₄ZrO₂/C membrane electrode assembly (MEA) was less than that of the Pt/C MEA. The RDE results demonstrated that the oxygen reduction reaction (ORR) activity of the as-prepared Pt₄ZrO₂/C is nearly the same as TKK-Pt/C. The XRD and TEM results showed that Pt₄ZrO₂/C catalyst presented higher sintering resistance than commercial Pt/C catalyst during the potential sweep test. This may be attributed to the addition of ZrO₂, which acts an anchor to inhibit the adjacent platinum particles to agglomerate. The ICP-AES results of Pt₄ZrO₂/C cathode catalyst before and after the potential sweep test showed that the composition of Pt and Zr were very near the nominal atomic ratio of Pt:Zr, which reflected that Pt₄ZrO₂/C catalyst had a good stability during the potential sweep test. In brief, the preliminary results indicate that Pt₄ZrO₂/C catalyst is a good candidate of Pt/C catalyst in high temperature PEMFC based on H₃PO₄ doped PBI for achieving longer cell life-time and higher cell performance.     

硼掺杂碳化硅负载Pt催化剂的甲醇电催化氧化性能

以硼掺杂碳化硅(B0.1SiC)为载体,采用循环伏安法在B0.1SiC载体上电沉积Pt纳米粒子制备了Pt/B0.1SiC催化剂。利用X射线光电子能谱、X射线衍射、氮气吸附-脱附、扫描电镜及透射电镜等测试方法对催化剂的晶型、表面性质及形貌进行了表征。结果表明,硼原子掺杂进入SiC晶格并取代了Si位点,使B0.1SiC载体的导电性增强;Pt纳米粒子均匀地分布在B0.1SiC载体上,平均粒径为2.7 nm。与相同条件下制备的Pt/SiC催化剂相比,Pt/B0.1SiC具有较大的电化学活性表面积、更高的甲醇催化氧化活性和稳定性。     

Cyanamide-derived non-precious metal catalyst for oxygen reduction

Cyanamide was used in the preparation series of metal–nitrogen–carbon (M–N–C) oxygen reduction catalysts. The best catalyst, treated at 1050 °C, shows good performance versus previously reported non-precious metal catalysts with an OCV ~ 1.0 V and a current density of 105 mA/cm² (iR-corrected) at 0.80 V in H₂/O₂ fuel cell testing (catalyst loading: 4 mg cm^? 2). Although nitrogen content has been previously correlated positively with ORR activity, no such trend is observed here for any nitrogen type. The combined effects of nitrogen and sulfur incorporation into the carbon may account for the high activity of the 1050 °C catalyst.     

High Pt utilization PEMFC electrode obtained by alternative ion-exchange/electrodeposition

High Pt utilization PEMFC electrodes were prepared by an alternative ion-exchange/electrodeposition (AIEE) technique. The results demonstrated that the MEA employing an AIEE electrode with a Pt loading of 0.014 mg Pt cm(-2) exhibits performance approximately 2.2 times larger than that employing a conventional Nafion-bonded Pt/C electrode with a same Pt loading.     

Novel preparation of polyphosphazene-coated carbon nanotubes as a Pt catalyst support

This study reports a noncovalent functionalization of MWCNTs with a fluorinated cross-linked polymer coating of poly[cyclotriphosphazene-co-(4,4'-(hexafluoroisopropylidene)diphenol)] and their application as the support of Pt for electrocatalytic oxidation of methanol.     

Phthalimido-prolinamide: a new chiral catalyst for solvent free enantioselective aldol reactions

A new prolinamide derivative phthalimido-prolinamide 1 was developed for organocatalytic enantioselective direct aldol reactions of various aldehydes with ketones. The catalytic protocol is effective with 15 mol % of catalyst under solvent free and additive free reaction conditions. By employing a catalytic amount of water, the efficiency of the reaction increased further and the desired products β-hydroxy carbonyl compounds were obtained in high yields and stereoselectivities.     

p-TsOH mediated solvent and metal catalyst free synthesis of nitriles from aldehydes via Schmidt reaction

A new and efficient protocol for the conversion of aldehyde into nitriles by modified Schmidt reaction. The reaction is carried out under solvent free condition using sodium azide as a source of nitrogen and catalysed by p-toluene sulphonic acid in presence of silica surface with no side product. This transformation gives good to excellent yield for numerous aromatic, aliphatic and heterocyclic nitriles using very simple reagent. This method has avoided the use of transition metal catalyst, toxic cyanide, hazardous solvent and offers a greener, simple and environment friendly procedure.     

Remarkable support effect of SWNTs in Pt catalyst for methanol electrooxidation

Carbon nanotubes have been proposed as advanced metal catalyst support for electrocatalysis. In this work, different carbon support materials including single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) and XC-72 carbon black, were compared in terms of their electrochemical properties using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The SWNTs is found to exhibit the highest accessible surface area in electrochemical reactions and the lowest charge transfer resistance at the SWNTs/electrolytes. These carbon materials are then loaded with varying amount of Pt by the electrodeposition technique to prepare carbon supported Pt catalysts. Electrochemical measurements of methanol oxidation reveal that the SWNTs supported Pt catalyst exhibits the highest mass activity (mA/mg-Pt). In comparison with Pt-XC-72 and Pt-MWNTs, the remarkably enhanced electrocatalytic activity of the Pt-SWNTs maybe attributed to a higher dispersion and utilization of the Pt particles, which are directly related to the electrochemical characteristics of SWNTs. The high concentration of oxygen-containing functional groups, high accessible surface area, low charge transfer resistance at the carbon/electrolyte interfaces can be important for the Pt dispersing and strong metal-support interaction in the Pt-SWNTs catalyst.     

Why is metallic Pt the best catalyst for methoxy decomposition?

The decomposition of methoxy on Cu(111), Ag(111), Au(111), Ni(111), Pt(111), Pd(111), and Rh(111) has been studied in detail by the density functional theory calculations. The calculated activation barriers were successfully correlated with the coupling matrix element V 2 ad and the d-band center (ε d ) for the group IB metals and group VIII metals, respectively. By comparison of the activation energy barriers of the methoxy decomposition on different metals, it was found that Pt is the best catalyst for methoxy decomposition. The possible reason why the metallic Pt is the best catalyst has been analyzed from both the energetic data and the electronic structure information, that is, methoxy decomposition on Pt(111) has the largest exothermic behavior due to the closest p-band center of the CH 3 O among all metals after the adsorption.     

Graphene-xerogel-based non-precious metal catalyst for oxygen reduction reaction

Graphene-xerogel-based Co–N cathode catalyst (Co–N-GX) for the oxygen reduction reaction (ORR) was prepared through a simple approach. The Co–N-GX shows a more positive onset potential, higher cathodic density for the ORR in alkaline media than graphene-sheet-based Co–N catalyst (Co–N-GS), highlighting the importance of high specific surface area for improving the ORR performance. The proposed approach makes the Co–N-GX catalyst a non-precious metal cathode catalyst for fuel cells.     

Colloidal metal nanoparticles as a component of designed catalyst

Recent advances in the synthesis of colloidal metal nanoparticles of controlled sizes and shapes that are relevant for catalyst design are reviewed. Three main methods, based on colloid chemistry techniques in solution, i.e., chemical reduction of metal salt precursors, electrochemical synthesis, and controlled decomposition of organometallic compounds and metal-surfactant complexes, are used to synthesize metal nanoparticles. Their catalytic activity and selectivity depend on the shape, size and composition of the metal nanoparticles, and the support effect, as shown for many reactions in quasi-homogeneous and heterogeneous catalysis. A specially designed type of thermally stable catalysts--"embedded" metal catalysts, in which metal nanoparticles are isolated by porous support shells so that metal sintering is effectively avoided at high temperatures, are also introduced. The utilization of pre-prepared colloidal metal nanoparticles with tuned size, shape and composition as components of designed catalysts opens up new field in catalysis.     

Preparation of hydrogenation Pt/activated carbon catalyst from a platinum complex

Both H₂PtCl₆ and (-C₃ H₅)₂ Pt(II) were employed for preparation of Pt/activated carbon hydrogenation catalysts. The Pt distribution, Pt dispersity and catalytic activity in liquid phase hydrogenation were investigated. The catalysts prepared from the organometallic compound were found to have higher Pt dispersity and catalytic activity.

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H₂PtCl₆ (-C₃ H₅)₂ Pt(II) . Pt, Pt . , , .

     

Oxygen reduction reaction activity of monodispersed Pt nanoparticles-loaded carbon black catalyst prepared with a Pt carbonyl cluster anion

Pt nanoparticles-loaded carbon black (CB) was prepared from Pt carbonyl cluster complexes, and had much narrower size distribution than commercial Pt nanoparticles/CB. In the former the monodispersed Pt nanoparticles were highly dispersed on CB without aggregation even at high Pt loading of 80 wt.%. Hydrodynamic voltammograms in O₂-saturated 0.05 M H₂SO₄ solution at 30 °C showed that the onset potential of oxygen reduction reaction (ORR) current for the monodispersed Pt nanoparticles/CB electrode was more positive than that for a polycrystalline Pt electrode and similar to that for the commercial Pt nanoparticles/CB electrode. Moreover, the mass activity for ORR for the monodispersed Pt nanoparticles/CB electrode was ca. 4.9 times higher than that for the commercial Pt nanoparticles/CB electrode, clearly indicating that the control of size distribution of Pt nanoparticles is meaningful for reducing the Pt consumption.     

Microwave assisted solvent free amination of halo-(pyridine or pyrimidine) without transition metal catalyst

A solvent free direct amination of halo-(pyridine or pyrimidine) has been developed in good to high yields under computer-controlled microwave irradiation without transition metal catalyst. This reaction is a solvent and metal free, useful method for coupling of halo-(pyridine or pyrimidine) with pyrrolidine and piperidine derivatives by nucleophilic aromatic substitution (S_NAr).