Electrochemical and structural characterization of carbon-supported Pt-Pd bimetallic electrocatalysts prepared by electroless deposition

Electrochemical and structural characteristics of various Pt-Pd/C bimetallic catalysts prepared by electroless deposition (ED) methods have been investigated. Structural analysis was conducted by X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDS). Monometallic Pt or Pd particles were not detected by EDS, indicating the ED methodology formed only bimetallic particles. The size of the Pt-Pd bimetallic particles was smaller than those of a commercially available Pt/C catalyst. The morphology of the Pt on Pd/C catalysts was identified and corresponded to Pd particles partially encapsulated by Pt.The electrochemical characteristics of the lowest Pd loading catalyst (7.0% Pt on 0.5% Pd/C) for the oxygen reduction reaction (ORR) have been investigated by the rotating ring disk electrode technique. The electrochemical activity was equal or lower than the commercially available Pt/C catalyst; however, the amount of hydrogen peroxide observed at the ring was reduced by the Pd, suggesting that such a catalyst has the potential to decrease ionomer degradation in applications. The Pt on Pd/C catalysts also show a higher tolerance to ripening induced by potential cycling. Therefore, catalyst suitability cannot be judged solely by its initial performance; information related to specific degradation mechanisms is also needed for a more complete assessment.     

化学复合镀PANI/Cu导电聚合物复合材料

采用化学复合镀技术在尼龙塑料PA66表面沉积PANI/Cu复合镀层。研究了复合镀层与基体的结合力和导电性，采用SEM观察镀层微观结构和表面形貌，并与纯铜、PANI镀层进行了比较；讨论了镀波pH值和温度等施镀工艺条件对镀层导电性能的影响。结果表明，PANI／Cu复合镀层具有良好的导电率且与基体结合紧密；增大镀液pH值和提高施镀温度，则其导电率增大。     

Pt nanowires prepared via a polymer template method: Its promise toward high Pt-loaded electrocatalysts for methanol oxidation

Platinum nanowires were prepared via a template-synthesis method by electrodeposition of platinum within pores of a track-etched polycarbonate (PCTE) membrane, followed by chemical etching to separate the Pt nanowires from the polymer. The structure and morphology of the Pt nanowires were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), revealing a polycrystalline phase with nanowire dimension up to 6 μm long and ca. 47 ± 9.8 nm of diameter. The unsupported Pt nanowires showed the better electrochemical mass activities over the methanol electro-oxidation than supported or unsupported Pt nanoparticles under the high Pt content-loaded conditions that is typically required for direct methanol fuel cells. This enhancement could be rationalized by its unique physicochemical and electrical properties arising from the inherent anisotropic one-dimensional (1D) nanostructure, such as charge transfer facilitation by reducing number of particle interfaces and more efficient use of Pt by alleviating fraction of embedded catalysts.     

CO oxidation on non-alloyed Pt and Ru electrocatalysts prepared by the polygonal barrel-sputtering method

The CO oxidation on non-alloyed Pt and Ru electrocatalysts prepared by the polygonal barrel-sputtering method was investigated. Samples were prepared by sputtering Pt and Ru separately at room temperature. From the X-ray diffraction (XRD) measurement of the sample prepared on a SiO₂ glass plate, it was found that the sputtered metals are non-alloyed. Subsequently, the non-alloyed Pt and Ru electrocatalysts were prepared by the polygonal barrel-sputtering method using carbon powder as a support. The XRD patterns of these samples showed a single and very broad peak supporting the hypothesis of the non-alloyed Pt and Ru. No separate Ru reflections were visible, which could be attributed to Ru particle sizes smaller than 4 nm, as obtained by transmission electron microscopy (TEM). CO oxidation on the non-alloyed Pt and Ru electrocatalysts were evaluated by CO stripping voltammetry. This measurement revealed that the lower peak potential of CO oxidation varies, depending on the Pt content and the sputtering order. In addition, it was assumed that the CO oxidation reaction site for non-alloyed Pt and Ru electrocatalyst has a limited area including direct contact sites between the Pt and Ru particles.     

Preparation and characterization of successively deposited Pt/Ru bimetallic electrocatalysts for the methanol oxidation

Two types of Pt/Ru electrocatalysts, which have different structural characteristics, were prepared with different synthetic routes. That is, Pt/Ru electrocatalysts were synthesized by the coreduction and successive deposition methods, respectively. The structural and catalytic properties of Pt/Ru electrocatalysts were characterized by XRD, TEM, voltammetry and chronoamperometry. From the XRD analysis, coreduced and successively deposited Pt/Ru electrocatalysts had an alloyed structure. TEM analyses showed that all the electrocatalysts had a highly dispersed state on the Vulcan XC-72R substrate. From the voltammetry, the coreduced electrocatalysts displayed higher catalytic activity than the successively deposited electrocatalysts for the electrooxidation of methanol. These results explain why coreduced catalysts are better able to dehydrogenate methanol and have a greater CO tolerance than the successively deposited ones. But chronoamperometry showed that successively deposited Pt/Ru electrocatalysts had stability similar to that of the coreduced ones. Although the successively deposited electrocatalysts showed lower catalytic activity than the coreduced ones, their enhanced catalytic activity was obtained by the successive deposition method in the comparison of methanol oxidation current density with pure platinum electrocatalyst.     

Composite electrocatalysts for anodic methanol and methanol-reformate oxidation

Binary anode electrocatalyst formulations were prepared by adsorption of phthalocyanine and tetraphenylporphyrin complexes of different transition metals on a commercial carbon supported platinum catalyst. Only after pyrolyzing the complexes at 700 °C under nitrogen were catalysts of some activity obtained. A binary Pt/Ni electrocatalyst prepared by this procedure exhibits considerable anodic catalytic activity in the acidic environment of the Nafion^® electrolyte for reformate and direct methanol oxidation for more than 400 h without deterioration. Ternary electrocatalyst formulations Pt/Ru/W = 1/1/y were produced according to the Bönnemann method. The Pt/Ru/W catalyst of 1/1/1.5 (mol/mol/mol) composition is optimal. Compared to the Pt/Ru catalyst, it enhances the performance of reformate (H₂ + 150 ppm CO) fuel cells by 50% and of direct methanol fuel cells (steam/methanol vapour = 50:1 mol/mol) by 80%. Attached to a GC electrode by a thin Nafion^® film, the catalysts were also tested for methanol oxidation in aqueous methanol solutions in half cells by slow potential stepping. This procedure is useful for fast initial screening.     

Enhanced electrochemical activity of Pt nanowire network electrocatalysts for methanol oxidation reaction of fuel cells

In this work, Pt nanowire networks supported on high surface area carbon (Pt NWNs/C) are synthesized as electrocatalysts for direct methanol fuel cells (DMFCs). The electrocatalytic behavior of Pt NWNs/C catalysts for the methanol and adlayer CO oxidation reactions is investigated and the results are compared with the Pt nanoparticles (NPs) supported on carbon (Pt NPs/C). The results indicate that Pt NWNs are characterized by interconnected nanoparticles with large number of grain boundaries, downshifted d-band center and reduced oxophilicity, which results in the enhanced surface mobility of oxygen-containing species such as CO_ads and OH_ads. The enhanced surface mobility of CO_ads and OH_ads in turn facilitates the removal of intermediate CO species during the methanol oxidation. The activity of the Pt NWNs/C electrocatalyst for the methanol oxidation reaction and electrooxidation of adsorbed CO is also evaluated by cyclic voltammetry, CO stripping, and kinetic analysis. The results show that Pt NWNs/C catalysts have a significantly higher electrocatalytic activity for the methanol oxidation reaction as compared to Pt NPs/C catalysts. The enhanced electrocatalytic activity of Pt NWNs/C catalysts is mainly due to the existence of large number of the grain boundaries of the interconnected nanoparticles of the unique Pt NWN structure.     

Enhanced activity and interfacial durability study of ultra low Pt based electrocatalysts prepared by ion beam assisted deposition (IBAD) method

Ultra low loading noble metal (0.04–0.12 mg_Pt/cm²) based electrodes were obtained by direct metallization of non-catalyzed gas diffusion layers via dual ion beam assisted deposition (IBAD) method. Fuel cell performance results reported earlier indicate significant improvements in terms of mass specific power density of 0.297 g_Pt/kW with 250 Å thick IBAD deposit (0.04 mg_Pt/cm² for a total MEA loading of 0.08 mg_Pt/cm²) at 0.65 V in contrast to the state of the art power density of 1.18 g_Pt/kW using 1 mg_Pt(MEA)/cm² at 0.65 V. In this article we report the peroxide radical initiated attack of the membrane electrode assembly utilizing IBAD electrodes in comparison to commercially available E-TEK (now BASF Fuel Cell GmbH) electrodes and find the pathway of membrane degradation as well. A novel segmented fuel cell is used for this purpose to relate membrane degradation to peroxide generation at the electrode/electrolyte interface by means of systematic pre and post analyses of the membrane are presented. Also, we present the results of in situ X-ray absorption spectroscopy (XAS) experiments to elucidate the structure/property relationships of these electrodes that lead to superior performance in terms of gravimetric power density obtained during fuel cell operation.     

Electrodeposition of porous Co layers and their conversion to electrocatalysts for methanol oxidation by spontaneous deposition of Pd

Electrocatalysts for methanol oxidation were prepared through a two stage deposition process: porous cobalt layers were deposited, by cathodic reduction of Co²⁺ ions, and then modified by spontaneous deposition of Pd. A basic sulphate solution and a mildly acid chloride solution were compared as media for the electrodeposition of Co. Deposits with the highest surface roughness were obtained in the chloride solution, at large current densities. Pd was deposited onto the Co porous layers by immersing them in acid deaerated PdCl₂ solutions, at open circuit. The Pd loading and the Pd surface area were estimated by UV–visible spectroscopy and by cyclic voltammetry, respectively. The Pd-modified Co electrodes were tested as anodes for methanol oxidation and compared to the similarly prepared Pd-modified Ni electrodes. The former exhibited better stability of performance and higher methanol oxidation peak currents per unit Pd mass, ca. 200 A g⁻¹.     

微波法制备的Pt/C催化剂对甲醇和CO的电催化氧化

用微波间断升温法制备了3种Pt/C催化剂,运用循环伏安和线行扫描方法测试甲醇和吸附态CO在不同方法制备的Pt/C催化剂上的电催化氧化情况。发现在酸性溶液中,对于相同Pt载量的Pt(2)和Pt(3)催化剂,Pt(3)具有较小的Pt平均粒径及较高的电催化活性;对于具有较高Pt载量的Pt(1)催化剂,具有最小的平均粒径和最高的电催化活性。     

置换化学镀法制备银包铜粉导电胶填料及其性能

对平均粒径为15μm的铜粉进行置换化学镀银,得到球状银包铜粉导电填料。对不同温度下银负载量随置换反应时间的变化曲线进行拟合得到不同温度下的反应速率常数,进而通过Arrhenius方程算得置换反应的活化能为1.9×10³ J/mol。表征了不同温度下制备的银包铜粉的微观形貌和晶体结构,以及将其作为填料时导电胶的性能。结果表明,所得银包铜粉为银白色,银层包覆完整,分散性良好。银包铜粉的质量分数为55%时,导电胶的抗氧化性和导电性良好;银包铜粉质量分数为55%～65%时,导电胶的剪切强度满足电子工业的一般要求。     

Preparation and characterization of Pt nanowire by electrospinning method for methanol oxidation

Pt nanowires are prepared by treating electrospun polyvinyl pyrrolidone (PVP)-Pt composite fibers at high temperatures in an air atmosphere and their activities toward a methanol oxidation reaction (MOR) are investigated. Thermogravimetric analysis (TGA) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) results indicate that the electrospun PVP-Pt composite fibers thermally decompose at 250 °C, which leads to the removal of 98 wt% of the PVP polymer and the simultaneous reduction of the Pt precursor to a Pt nanowire. The physical and electrochemical properties of Pt nanowires are found to be affected by the heat treatment conditions such as heating rate, time, temperature, and atmosphere. Furthermore, polymer fibers subjected to a pyrolization process in nitrogen followed by exposure to an air atmosphere enhance the surface area of the Pt nanowires, leading to high electrochemical activity toward a MOR. The detailed physical and electrochemical properties of the Pt nanowires are characterized by various spectroscopic and electrochemical techniques, and the possibilities of using them as electrocatalysts in a fuel cell are explored.     

Exfoliated graphene-supported Pt and Pt-based alloys as electrocatalysts for direct methanol fuel cells

To greatly improve the electrocatalytic activity for methanol oxidation, high-quality exfoliated graphene decorated with uniform Pt nanocrystals (NCs) (3 nm) have been prepared by a very simple, low-cost and environmentally benign process. During the entire process, no surfactant and no halide ions were involved, which not only enabled very clean surface of Pt/graphene leading to excellent conductivity, but also greatly improved the electrocatalyst tolerance to carbon monoxide poisoning (Pt/graphene, I_f/I_b = 1.197), compared to commercial Pt/C (I_f/I_b = 0.893) catalysts. To maximize the electrocatalytic performance and minimize the amount of precious Pt, Pt–M/graphene (M = Pd, Co) hybrids have also been prepared, and these hybrids have much larger electrochemically active surface areas (ECSA), which are 4 (PtPd/graphene) and 3.3 (PtCo/graphene) times those of commercial Pt/C. The PtPd/graphene and PtCo/graphene hybrids also have remarkably increased activity toward methanol oxidation (I_f/I_b = 1.218 and 1.558). Furthermore, density functional theory (DFT) simulations demonstrate that an electronic interaction occurred between Pt atoms and graphene, indicating that graphene substrate plays a crucial role in regulating the electron structure of attached Pt atom, which confirmed that the increased efficiency of methanol oxidation was due to the synergetic effects of the hybrid structure.     

A study of the Co-coated Ni cathode prepared by electroless deposition for MCFCs

In this study, we made a novel alternative cathode material of molten carbonate fuel cell (MCFC) using electroless deposition of Co on the surface of the Ni powder. Using this manufacturing method, we expect that economical and large-scale cathode can be made easily. The cathode prepared by this method formed LiCo_1−yNi_yO₂ phase in molten (Li_0.62K_0.38)₂CO₃ at 650 °C under CO₂:O₂=66.7:33.3% atmosphere, its solubility is 40% lower than that of NiO cathode. In the unit cell test, the performance of the cell composed of Co-coated Ni cathode was same as that of the cell composed of NiO cathode. Thus the cathode made by Co-coated Ni powder used as an alternative cathode can maintain the advantages of NiO cathode and lengthen the lifetime of MCFC.     

The study of Pt@Au electrocatalyst based on Cu underpotential deposition and Pt redox replacement

Electrochemical study of the decorated Pt@Au catalyst synthesized by Cu underpotential deposition (UPD)-Pt redox replacement technique has been conducted in this work. The parameters affecting the Cu UPD on Au/C nanoparticles in sulfuric acid electrolyte, including the UPD potential, deposition time and potential sweep rate, were investigated in detail. Anode stripping method was used to calculate the charge of the deposited Cu adlayers. Results showed that Pt@Au catalyst prepared by this UPD-redox replacement approach is not a core-shell structure but a decorated structure. A series of decorated Pt@Au/C catalysts with various Pt coverages were synthesized and examined for formic acid oxidation (FAO). It is found that the specific activity of Pt atoms increases with the decrease of Pt surface coverage on Au. Life test showed that better stability was pertained for this decorated Pt@Au/C catalyst compared to Pt/C towards FAO.     

Density functional theory study on the oxidation mechanisms of aldehydes as reductants for electroless Cu deposition process

The oxidation mechanism of aldehydes, which are commonly used as reductants for an electroless deposition process, was studied by using Density Functional Theory (DFT) calculations. The reaction pathway of the three aldehydes, i.e., formaldehyde, acetaldehyde and glyoxylic acid, with different functional groups, were examined by calculating energy profiles of all intermediate species. It was indicated that the pathway in an isolated system proceeds via dianion-free intermediate species. Taking the solvation effect into consideration, it was indicated that the oxidation reactions of the three aldehydes preferably proceed at the solid/liquid interface. In combination with a Cu metal cluster as a model of metal surface, it was also indicated that the oxidation reactions proceed preferentially at the Cu surface. It was expected that the adsorption/desorption energy at the Cu surface of glyoxylic acid, which has an electron-accepting carboxyl group, was smaller and substituent effect lead to its high reducibility.     

Carbon-supported manganese oxide nanoparticles as electrocatalysts for oxygen reduction reaction (orr) in neutral solution

Manganese oxides (MnO _x ) catalysts were chemically deposited onto various high specific surface area carbons. The MnO _x /C electrocatalysts were characterised using a rotating disk electrode and found to be promising as alternative, non-platinised, catalysts for the oxygen reduction reaction (ORR) in neutral pH solution. As such they were considered suitable as cathode materials for microbial fuel cells (MFCs). Metal [Ni, Mg] ion doped MnO _x /C, exhibited greater activity towards the ORR than the un-doped MnO _x /C. Divalent metals favour oxygen bond splitting and thus orientate the ORR mechanism towards the 4-electron reduction, yielding less peroxide as an intermediate.     

Preparation of Pt/C catalysts by electroless deposition for proton exchange membrane fuel cells

The aim of this research is to study the effect of different preparation conditions for making carbon supported platinum catalysts by electroless deposition on the properties and performance of proton exchange membrane fuel cells (PEMFC). The studied parameters are platinum and formaldehyde concentrations, deposition time and the method of formaldehyde addition. By a univariate approach, the optimal preparation conditions of 20 wt% Pt/C catalyst are determined as using 10 g Pt l ⁻¹, two hours of deposition time and seven equally spaced additions of 0.15 M formaldehyde. SEM and TEM results indicate that the Pt/C catalyst attained has a small particle size (2–4 nm) and a good dispersion. The efficiency of the activation polarization of membrane electrode assembly (MEA) using these prepared catalysts is nearly that of commercial electrodes, but they have a significantly higher ohmic loss.     

Templated Pt-Sn electrocatalysts for ethanol, methanol and CO oxidation in alkaline media

In this work, we have investigated an aerosol-derived templated electrocatalyst for electro-oxidation of small organic molecules in alkaline media. Templated Pt-Sn electrocatalysts are compared to templated Pt catalysts both synthesized in an aerosol synthesis technique. In this synthesis approach, mono-disperse silica nanoparticles are used to template the metallic precursors. Structural and compositional analysis of the nanostructured materials are performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET surface area measurements. The aerosol-derived templated electrocatalysts are examined in conjunction with an anion exchange ionomer for ethanol, methanol and CO oxidation in alkaline media. The electrochemical studies include cyclic voltammetry, chronoamperometry and voltammetric adsorption of adsorbed CO.