碳化钨/碳气凝胶纳米复合材料增强Pt电催化甲醇性能的研究

以间苯二酚和甲醛为原料,采用溶胶-凝胶法原位合成WC纳米颗粒制备了碳化钨/碳气凝胶(WC/CAs);以WC/CAs为载体,利用微波加热乙二醇还原法制备了Pt/WC/CAs催化剂。运用循环伏安法(CV)、线性扫描(LSV)、计时电流法(CA)、能谱(EDS)、透射电子显微镜(TEM)和X射线衍射(XRD)等技术分析Pt/WC/CAs催化剂的组成、结构及其对甲醇的电催化氧化活性的影响。实验结果表明,载体中WC纳米颗粒的加入促进Pt贵金属颗粒对甲醇的电催化氧化活性,正扫电流峰ip与扫描速率的平方根v1/2线性相关,Pt/WC/C催化氧化甲醇的过程受扩散控制;且电催化活性比Pt/C要好。     

Improving the Stability and Ethanol Electro‐Oxidation Activity of Pt Catalysts by Selectively Anchoring Pt Particles on Carbon‐Nanotubes‐Supported‐SnO2

To improve the stability and activity of Pt catalysts for ethanol electro‐oxidation, Pt nanoparticles were selectively deposited on carbon‐nanotubes (CNTs)‐supported‐SnO₂ to prepare Pt/SnO₂/CNTs and Pt/CNTs was prepared by impregnation method for reference study. X‐ray diffraction (XRD) was used to confirm the crystalline structures of Pt/SnO₂/CNTs and Pt/CNTs. The stabilities of Pt/SnO₂/CNTs and Pt/CNTs were compared by analyzing the Pt size increase amplitude using transmission electron microscopy (TEM) images recorded before and after cyclic voltammetry (CV) sweeping. The results showed that the Pt size increase amplitude is evidently smaller for Pt/SnO₂/CNTs, indicating the higher stability of Pt/SnO₂/CNTs. Although both catalysts exhibit degradation of electrochemical active surface area (EAS) after CV sweeping, the EAS degradation for the former is lower, further confirming the higher stability of Pt/SnO₂/CNTs. CV and potentiostatic current–time curves were recorded for ethanol electro‐oxidation on both catalysts before and after CV sweeping and the results showed that the mass specific activity of Pt/CNTs increases more than that of Pt/SnO₂/CNTs, indicating that Pt/CNTs experiences more severe evolution and is less stable. The calculated area specific activity of Pt/SnO₂/CNTs is larger than that of Pt/CNTs, indicating SnO₂ can co‐catalyze Pt due to plenty of interfaces between SnO₂ and Pt.     

Combinatorial Search for Quaternary Methanol Tolerant Oxygen Electro‐Reduction Catalyst

A combinatorial library containing 645 different compositions was synthesised and characterised for methanol tolerant oxygen electro‐reduction reaction (ORR) catalytic performance. The library was composed of compositions involving between 1 and 4 metals among Pt, Ru, Fe, Mo and Se. In an optical screening test, Pt(50)Ru(10)Fe(20)Se(10) composition exhibited the highest ORR activity in the presence of methanol. This composition was further investigated by synthesis and characterisation of a powder version catalyst [Pt(50)Ru(10)Fe(20)Se(10)/C]. At 0.85 V [vs. reversible hydrogen electrode (RHE)] in the absence of methanol, the Pt/C catalyst exhibited higher ORR current (0.0990 mA) than the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst (0.0902 mA). But much higher specific activity (12.7 μA cm_pt^–2) was observed in the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst than for the Pt/C catalyst 6.51 μA cm_pt^–2). In the presence of methanol, the ORR current decreased by 0.0343 and 0.247 mA for the Pt(50)Ru(10)Fe(20)Se(10)/C and Pt/C catalysts, respectively, which proved the excellent methanol tolerance of the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst.     

Study of Methanol‐tolerant Oxygen Reduction Reaction at Pt–Bi/C Bimetallic Nanostructured Catalysts

The nanostructured platinum–bismuth catalysts supported on carbon (Pt₃Bi/C, PtBi/C and PtBi₃/C) were synthesised by reducing the aqueous metal ions using sodium borohydride (NaBH₄) in presence of a microemulsion. The amount of metal loading on carbon support was found to be 10 wt.‐%. The catalyst materials were characterised by X‐ray diffraction (XRD), X‐ray fluorescence (XRF), transmission electron microscope (TEM) and electroanalytical techniques. The Pt₃Bi/C, PtBi/C and PtBi₃/C catalysts showed higher methanol tolerance, catalytic activity for oxygen reduction reaction (ORR) than Pt/C of same metal loading. The electrochemical stability of these nano‐sized catalyst materials for methanol tolerance was investigated by repetitive cycling in the potential range of –250 to 150 mV_MSE. Bi presents an interesting system to have a control over the activity of the surface for MOR and ORR. All Pt–Bi/C catalysts exhibited higher mass activities for oxygen reduction (1–1.5 times) than Pt/C. It was found that PtBi/C catalyst exhibits better methanol‐tolerance than the other catalysts.     

Evaluation of the Performance of Carbon Supported Pt–Ru–Ni–P as Anode Catalyst for Methanol Electrooxidation

This research is aimed to improve the activity and stability of ternary alloy Pt–Ru–Ni/C catalyst. A novel anodic catalyst for direct methanol fuel cell (DMFC), carbon supported Pt–Ru–Ni–P nanoparticles, has been prepared by chemical reduction method by using NaH₂PO₂ as a reducing agent. One glassy carbon disc working electrode is used to test the catalytic performances of the homemade catalysts by cyclic voltammetric (CV), chronoamperometric (CA) and amperometric i–t measurements in a solution of 0.5 mol L^–1 H₂SO₄ and 0.5 mol L^–1 CH₃OH. The compositions, particle sizes and morphology of home‐made catalysts are evaluated by means of energy dispersive analysis of X‐ray (EDAX), X‐ray diffraction (XRD) and transmission electron micrographs (TEM), respectively. TEM images show that Pt–Ru–Ni–P nanoparticles have an even size distribution with an average diameter of less than 2 nm. The results of CV, CA and i–t curves indicate that the Pt–Ru–Ni–P/C catalyst shows significantly higher activity and stability for methanol electrooxidation due to the presence of non‐metal phosphorus in comparison to Pt–Ru–Ni/C one. All experimental results indicate that the addition of non‐metallic phosphorus into the Pt–Ru–Ni/C catalyst has definite value of research and practical application for enhancing the performance of DMFC.     

Facile Preparation of an Excellent Pt/RuO2‐MnO2/CNTs Nanocatalyst for Anodes of Direct Methanol Fuel Cells

RuO₂‐MnO₂ complex supported by multi‐wall carbon nanotubes (CNTs) was firstly synthesised by the oxidation–reduction precipitation of RuCl₃ and KMnO₄ in one step. Then Pt was loaded onto the obtained RuO₂‐MnO₂/CNTs to fabricate a novel anodic catalyst Pt/RuO₂‐MnO₂/CNTs for direct methanol fuel cells (DMFCs). The catalyst was characterised by transmission electron microscopy (TEM), X‐ray diffraction (XRD), temperature programmed reduction (TPR), X‐ray photoelectron spectroscopy (XPS) and BET specific surface areas (BET). Pt nanoparticles were found uniformly dispersed on the surface of CNTs, with the average diameter of about 2.0 nm. The activities of methanol and CO electrocatalytic oxidation were analysed, and the reaction mechanism of methanol electro‐oxidation on Pt/RuO₂‐MnO₂/CNTs catalyst was discussed. The MnO₂ in the catalysts improves the proton conductivity and electrochemical active surface area (EAS) for the catalysts. RuO₂ improves the CO oxidation activity and Pt dispersion. CNTs provide effectively electron channels. Thus, the Pt/RuO₂‐MnO₂/CNTs catalyst has high utilisation of the noble metal Pt, high CO oxidation ability and excellent methanol electro‐oxidation activity, being an outstanding anode catalyst for DMFC.     

Synthesis and Characterization of Pt/C Nanocatalysts Using Room Temperature Ionic Liquids for Fuel Cell Applications

Carbon supported Pt nanocatalysts are prepared using different room temperature ionic liquids (RTILs) as the solvent and conventional preparation techniques, based on wet impregnation methods. The Pt/C nanocatalysts are characterized by XRD, TEM, EDX, and XPS. The results of the analyses show that the Pt/C catalysts, using different RTILs as solvents, are homogeneously dispersed with a narrow size distribution. The electro‐oxidation of liquid methanol on these catalysts is investigated at room temperature by cyclic voltammetry and chronoamperometry. The results have shown that the Pt/C catalysts prepared using RTILs are more active than the other Pt/C catalysts prepared by the authors. Surface area measurements of the Pt metal, conducted by electro‐oxidation of preadsorbed CO, indicate that catalysts prepared using RTILs as the solvents have higher surface area. The Pt/C nanocatalysts, prepared using RTILs, exhibit enhanced activity for the methanol oxidation reaction, compared with the Pt/C catalysts prepared by the impregnation method and commercial Pt/C catalysts.     

Polyaniline–13X zeolite composite‐supported platinum electrocatalysts for direct methanol fuel cell applications

We successfully synthesized 13X zeolite using a hydrothermal method. Then, composites of polyaniline (PANI) with 13X zeolite and PANI–13X with platinum were prepared by chemical oxidative polymerization and chemical reduction, respectively. Field emission scanning electron microscopy, X‐ray diffraction, Raman spectroscopy and Brunauer–Emmett–Teller techniques were used to characterize the PANI–Pt and PANI–Pt–13X composites. Further, the electrocatalytic activity towards methanol oxidation of the synthesized catalysts was explored using cyclic voltammetry in 1 mol L^?1 CH₃OH + 0.5 mol L^?1 H₂SO₄ solution. From the obtained results, PANI–Pt–13X shows superior performance compared to PANI–Pt towards methanol oxidation and electrical conductivity. Hence, the 13X zeolite‐incorporated PANI–Pt composite could be an efficient catalyst for direct methanol fuel cell applications. © 2019 Society of Chemical Industry     

Graphite Electrodes Modified with Platinum‐Nickel Nano‐Particles for Methanol Oxidation

Methanol electro‐oxidation is investigated at graphite electrodes modified with various platinum and nickel nano‐particle deposits using cyclic voltammetry. The modified electrodes are prepared by the simultaneous electrodeposition of metals from their salt solutions using potentiostatic and galvanostatic techniques. They show enhanced catalytic activity towards methanol oxidation in KOH solution. The catalytic activity of platinum nano‐particles is found to be significantly affected by the presence of relatively small amounts of nickel deposits. A comparison is made between the electrocatalytic activity of Pt/C and (Pt‐Ni)/C electrodes. The results show that the methanol electro‐oxidation current increases with an increase in the nickel content. In particular, the highest catalytic activity is achieved for platinum to nickel deposits of 95%:5% (wt.‐%), in other cases the catalytic activity decreases. It is found that Ni enhances the catalytic activity of Pt by increasing the number of active sites, as well as through an electron donation process from Ni to Pt. This process takes place once the nickel hydroxide (Ni(OH)₂)/nickel oxy‐hydroxide (NiOOH) transformation begins. The effect of the methanol concentration on the methanol oxidation reaction is investigated. The order of reaction, with respect to methanol, at the modified (Pt‐Ni)/C electrode is found to be 0.5.     

Synthesis of Ultrafine Size Platinum Nanoparticles on Defective Graphene with Enhanced Performance Towards Methanol Electro‐Oxidation

Graphene nanosheets (GS) were formed by the thermal‐expansion method. Large micropores about 1–2 nm were produced, which might provide abundant anchor sites for fixing catalyst. Platinum nanoparticles (NPs) supported on exfoliated GS (Pt/GS) were synthesized through an improved impregnation approach and mixture gas (5% H₂ in N₂) reduction. SEM and TEM images indicated the simple and clean method can effectively synthesize Pt with uniform dispersion and small size (below 3 nm) on the 2D specific and stratiform GS. The different amounts of Pt loaded on carbon carriers have been investigated respectively to evaluate the preferable electrocatalyst. Experimental results showed that Pt/GS of 20 wt.% initiated CO oxidation at the lowest onset potential in comparison with the commercial Pt/C (JM), indicating a higher CO tolerance of Pt/GS catalysts. In addition, Pt/GS of 20 wt.% exhibited enhanced electrocatalytic activity and high durability towards methanol oxidation. The high performance is exclusively attributed to synergistic effects of exfoliated GS and ultrafine size Pt NPs. Combining a melt‐diffusion strategy with the effective reduction of Pt precursors by the hydrogen gas, this present method is easy to scale up and possesses a significant potential for synthesizing anode electro‐catalyst of direct methanol fuel cells.     

WC/C制备条件对甲醇电氧化特性的影响研究

以钨酸铵为前躯体,采用程序升温控制还原法（TPR）制备了WC／C纳米颗粒,在碳载体存在的情况下,研究了钨源前躯体碳化过程中CH4与H2流量比对单-WC晶相以及Pt／WC／C电催化氧化甲醇性能的影响。XRD测试结果发现：仅在CH4：H2流量比为2时可获得单一WC多晶,其平均粒径为11．3nm。循环伏安实验结果证实：10wt％Pt-10wt％WC／C电催化氧化cH,OH的比质量活性达到875mA·mg^-1,远远高于10wt％Pt／C的658mA·mg^-1,且起始氧化电位负移80mV。计时电流法实验表明Pt／WC／C在酸性介值中稳定性高于Pt／C催化剂。     

Catalysts for Direct Methanol Fuel Cells

The activity of in house prepared carbon-supported Pt-Ru catalysts for methanol oxidation and carbon-supported RuSe for the oxygen reduction reaction in direct methanol fuel cells (DMFCs) was investigated. The composition of Pt-Ru/C was varied both in terms of weight loading (ratio of total metal content to carbon) as well as the ratio of Pt to Ru. The measurements were carried out in a half cell arrangement in sulphuric acid at various temperatures. The weight loading and ratio of Pt to Ru were varied in order to find out the optimum weight loading of precious metal and the temperature dependence of Pt to Ru ratio on methanol oxidation reaction. It has been found that there exists an optimum in the weight loading at 60 wt.% for carbon-supported Pt-Ru catalyst towards its maximum mass activity. While 1:1 Pt to Ru ratio exhibits a higher activity than 3:2 Pt:Ru above 60 °C, 3:2 ratio exhibits a higher activity at lower temperature. It has been observed that RuSe is inactive towards methanol and it is realised that RuSe is a potential candidate as methanol tolerant oxygen reduction catalyst. The activity of carbon supported RuSe for oxygen reduction reaction (ORR) was tested in sulphuric acid in the presence of methanol. Even though the mass specific activity of the RuSe catalyst is somewhat lower than that of Pt/C, the surface activity of carbon-supported RuSe is superior than that of carbon supported Pt which indicate the unfavourable size distribution of RuSe/C catalyst.     

Study on liquid‐phase hydrogenation of paranitrotoluene over Ru‐based catalysts

This paper presented a study on the role of yttrium addition to Ru‐based catalysts for liquid phase paranitrotoluene hydrogenation reaction. An impregnation‐precipitation method was used for preparation of a series of yttrium doped Ru/NaY catalysts with yttrium content in the range of 0.0026–0.0052 g/g. Properties of the obtained samples were characterized and analyzed by X‐ray diffraction (XRD), H₂‐TPR, Transmission electron microscopy (TEM), ICP atomic emission spectroscopy, and Nitrogen adsorption‐desorption. The results revealed that catalytic activity of NaY supported Ru catalysts increased with the yttrium content at first, then decreased with the further increase of yttrium content. When yttrium content was 0.0033 g/g, a Ru‐Y/NaY² catalyst showed the most excellent performance of paranitrotoluene hydrogenation reaction (paranitrotoluene conversion and the selectivity toward P‐methyl‐cyclohexylamine reached 99.9 % and 82.5 %, respectively). In addition, to compare with the performance of Ru‐Y/NaY catalysts, the active carbon supported Ru catalysts were prepared using the same method in view of its higher surface area and adsorption capacity. Finally, the effect of solvent on the reaction over Ru‐Y/NaY² catalyst has been investigated, it was found that the best performance of paranitrotoluene hydrogenation reaction took place in protic solvents (isopropanol and ethanol). This was mainly ascribed to their polarity and hydrogen‐bond accepting capability.

     

Synthesis of Novel Submicrometer‐Scale Flat Carbon Fibers and Application in the Electrooxidation of Methanol

Novel submicrometer‐scale flat carbon fibers (SFCF) have been synthesized by catalytic chemical vapor deposition of acetylene over an Ni‐Al layered double hydroxide (NiAl‐LDH) compound, and the electrochemical activity of Pt supported on as‐synthesized SFCF for methanol oxidation has been investigated. The materials were characterized by power X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, and cyclic voltammetry tests. The results reveal that the active crystal facets of the NiAl₂O₄ spinel phase derived from NiAl‐LDH can deposit carbon atoms to grow SFCF, and that the co‐growing Ni nanoparticles are not catalytically active for the formation of SFCF. Furthermore, after support with Pt, the resultant Pt/SFCF electrocatalyst shows much higher activity for methanol oxidation than the Pt/C one in both acid and alkaline media, which is attributed to the combined beneficial effects of the microstructure of the SFCF support, improved electrical conductivity originating from the NiAl₂O₄ spinel catalyst embedded in SFCF, and improved dispersion of Pt particles through exposed Ni nanoparticles adhering intimately to the SFCF.     

Selective Oxidation of Methanol to Dimethoxymethane over Mesoporous Al‐P‐V‐O Catalysts

The synthesis and application of bifunctional mesoporous Al‐P‐V—O catalysts with both acidic and redox sites for selective oxidation of methanol to dimethoxymethane (DMM) is described. The catalysts were characterized by N₂ adsorption/desorption, X‐ray diffraction, temperature‐programmed desorption, X‐ray photoelectron spectroscopy, and infrared spectroscopy. It is shown that porosity; redox property and surface acidity of the catalysts were greatly influenced by the Al/V/P ratio. The synergistic effect of phosphorus and vanadium was investigated. Al‐P‐V—O catalysts exhibited good catalytic activity because of the controlled reducibility and the acidic sites. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2587–2593, 2013     

SbOx‐promoted pt nanoparticles supported on CNTs as catalysts for base‐free oxidation of glycerol to dihydroxyacetone

Understanding of selective base‐free oxidation of glycerol to dihydroxyacetone (DHA) over Pt‐based catalysts is of paramount scientific and industrial importance. In this work, a comparative study between differently sized SbO_x‐promoted and unpromoted Pt/CNTs catalysts is carried out to decouple the promoter effects from the metal size effects. The introduction of SbO_x appears to enhance both the glycerol oxidation activity and the DHA selectivity, and the largely sized promoted Pt/CNTs catalysts afford a relatively high DHA yield and less C–C bond cleavage. X‐ray photoelectron spectroscopy measurements reveal that the Sb species are mainly in the form of SbO_x, and the differently sized promoted catalysts show similar metal binding energies. Furthermore, theoretical studies on the promotional effects of SbO_x are carried out by DFT calculations. It is found that the presence of the promoter on the catalyst surface favors the preferential activation of the secondary hydroxyl group. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3979–3987, 2018     

Optimum Pt and Ru atomic composition of carbon-supported Pt–Ru alloy electrocatalyst for methanol oxidation studied by the polygonal barrel-sputtering method

The optimum Pt and Ru atomic composition of a carbon-supported Pt–Ru alloy (Pt–Ru/C) used in a practical direct methanol fuel cell (DMFC) anode was investigated. The samples were prepared by the polygonal barrel-sputtering method. Based on the physical properties of the prepared Pt–Ru/C samples, the Pt–Ru alloy was found to be deposited on a carbon support. The microscopic characterization showed that the deposited alloy forms nanoparticles, of which the atomic ratios of Pt and Ru (Pt:Ru ratios) are uniform and are in accordance with the overall Pt:Ru ratios of the samples. The formation of the Pt–Ru alloy is also supported by the electrochemical characterization. Based on these results, methanol oxidation on the Pt–Ru/C samples was measured by cyclic voltammetry and chronoamperometry. The results indicated that the methanol oxidation activities of the prepared samples depended on the Pt:Ru ratios, of which the optimum Pt:Ru ratio is 58:42 at.% at 25 °C and 50:50 at.% at 40 and 60 °C. This temperature dependence of the optimum Pt:Ru ratio is well explained by the relationship between the methanol oxidation reaction process and the temperature, which is reflected in the rate-determining steps considered from the activation energies. It should be noted that at 25–60 °C, the Pt–Ru/C with Pt:Ru = 50:50 at.% prepared by our sputtering method has the higher methanol oxidation activity than that of a commercially available sample with the identical overall Pt:Ru ratio. Consequently, the polygonal barrel-sputtering method is useful to prepare the practical DMFC anode catalysts with the high methanol oxidation activity.     

Synthesis of Mesoporous Carbon from Okara and Application as Electrocatalyst Support

Carbon materials derived from biomass are economical and simple. Here, a okara‐derived carbon (ODC) was prepared by carbonized cheap and abundant okara at 800 °C in N₂ atmosphere. A high degree of graphitization, mesoporous structure and large specific surface area of ODC were proved by Raman spectroscopy, nitrogen adsorption–desorption isotherms, X‐ray diffraction, Fourier transform infrared spectra and scanning electron microscope. The ODC can be used as support of platinum nanoparticles, and the catalytic performance for methanol electro‐oxidation of its was measured by cyclic voltammetry and CO stripping voltammetry. The results showed that Pt/ODC catalyst had higher electrocatalytic activity and the resistance to poisoning ability toward methanol electrooxidation than the Pt/C catalyst prepared under the same conditions.     

Pd‐RuSe/C as ORR Specific Catalyst in Alkaline Solution Containing Methanol

Carbon supported RuSe (RuSe/C) catalyst in varying atomic ratios of Ru to Se, namely, 1:1, 2:1, and 3:1 were prepared and their performances were compared with carbon supported Ru (Ru/C). Based on the performance, Palladium was incorporated into as prepared RuSe(2:1)/C and heat treated HTRuSe(2:1)/C. Ru/C, RuSe/C, and Pd‐RuSe/C were characterized by X‐ray diffraction (XRD) and transmission electron microscopy techniques. The XRD analyses of Ru/C, RuSe/C and Pd‐HTRuSe/C show the formation of the hcp structure of Ru particles and the mean particle size was obtained from Ru(101) peak. The electrochemical characterizations of Ru/C, RuSe/C, Pd‐HTRuSe(2:1)/C and Pd‐RuSe(2:1)/C were conducted by cyclic voltammetry. Linear Sweep Voltammetric studies showed that incorporation of Pd in HTRu‐Se(2:1)/C resulted in better catalytic activity toward oxygen reduction with resistance to methanol oxidation. The quantity of hydrogen peroxide produced was obtained from rotating ring disk electrode studies.     

Preparation of Platinum‐Poly(O‐dihydroxybenzene) Composite Catalyst and Its Electrocatalytic Activity Toward Methanol and Formic Acid Oxidation

A composite catalyst has been successfully prepared by dispersing Pt nanoparticles on a poly(o‐dihydroxybenzene) (PoDHB) modified glassy carbon (GC) electrode and characterized by SEM, EDX, and electrochemical analysis. Compared with Pt nanoparticles deposited on the bare GC, the Pt/PoDHB/GC exhibits higher catalytic activity and stronger poisoning tolerance for electro‐oxidation of methanol and formic acid. The enhanced performance could be attributed to the increase of electrochemical active surface area (EASA) arisen from the PoDHB modification. Furthermore, performance limiting factors such as platinum loading, polymer mass, H₂SO₄, methanol, and formic acid concentrations have been evaluated for optimizing the electrocatalytic activities.