碳纳米管载PtPb、PtBi纳米催化剂对甲酸抗CO中毒的研究

混酸法预处理了载体碳纳米管（CNTs）,采用两步法制备PtPb/CNTs和PtB i/CNTs催化剂。以甲酸为研究对象,首次采用循环伏安法长时间连续性扫描的方法研究催化剂的抗CO中毒能力。研究发现,添加了Pb、B i金属后,增强了Pt/CNTs催化剂性能,如甲酸的起始氧化电位明显降低、氧化电流密度增大且抗毒性能增强。PtPb/CNTs、PtB i/CNTs催化甲酸的起始氧化电位都低于Pt/CNTs（0.099V）,依次为-0.108和-0.004V（Vs.Ag/AgC l）;在0.6V处,PtPb/CNTs、PtB i/CNTs催化氧化甲酸产生的电流密度都明显大于Pt/CNTs（0.79 mA/cm2）,依次为3.10和1.77mA/cm2;PtPb/CNTs、PtB i/CNTs催化剂的寿命依次为Pt/CNTs催化剂的4倍和5倍。本文主要进行燃料电池电催化剂材料的研究,对于制造新型电催化剂有一定的探索作用。     

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.     

Study on the growth of platinum nanowires as cathode catalysts in proton exchange membrane fuel cells

The platinum nanowires have been verified to be a promising catalyst to promote the performance of proton exchange membrane fuel cells.In this paper,accurately controlled growth of nanowires in a carbon matrix is achieved for reducing Pt loading.The effects of formic acid concentration and reaction temperature on the morphology and size of the Pt nanowires,as well as their electrochemical performances in a single cell,are investigated.The results showed that the increase in the formic acid concentration results in a volcano trend with the length of Pt nanowires.With increasing reduction temperature,the diameter of Pt nanowires increases while Pt particles evolve from one-dimensional to zero-dimensional up to 40°C.A mechanism of the Pt nanowires growth is proposed.The optimized Pt nanowires electrode exhibits a power density(based on electrochemical active surface area)79%higher than conventional Pt/C one.The control strategy obtained contributes to the design and control of novel nanostructures in nano-synthesis and catalyst applications.     

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.     

One-pot synthesis of PdBi/reduced graphene oxide catalyst under microwave irradiation used for formic acid electrooxidation

The Pd and PdBi nanoparticles dispersed on the reduced graphene oxide (Pd/rGO and PdBi/rGO) have been synthesized through one-pot reaction under the irradiation of microwave and the obtained composites have been characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and their electrocatalytic activities have also been evaluated. It is found that the PdBi_0.05/rGO catalyst exhibits higher activity and better stability toward formic acid electrooxidation compared with Pd/C and Pd/rGO. The excellent electrocatalytic performance indicates that the addition of appropriate amount of Bi can greatly enhance the activity and stability of Pd catalysts for the formic acid oxidation.     

Modification of Pt nanoelectrodes dispersed on carbon support using irreversible adsorption of Bi to enhance formic acid oxidation

In this work, formic acid oxidation on Pt nanoelectrodes modified by irreversible adsorption of Bi is presented. The coverage of Bi, as measured by voltammetry and X-ray photoelectron spectroscopy, was controlled from 0.05 to 0.25. Chronoamperometric measurement of the catalytic activities of the Bi-modified Pt nanoelectrodes revealed that the catalytic enhancement depended on oxidation potential and Bi coverage: elemental Bi in the potential range from −0.1 V to 0.6 V enhanced formic acid oxidation by factor of 4, while partially oxidized Bi in the potential range from 0.3 V to 0.7 V increased by factor of 8. The enhancement in the latter potential range was effective only when the Bi coverage was more than 0.18. Single cell performance of the Pt nanoelectrodes modified by Bi increased by factor of 2-3, depending on operation conditions such as formic acid concentration, temperature, and humidity in the feeding gas into cathode. When the Bi coverage was more than 0.18, the single cell performances were nearly identical. Based on measurement of adsorbed CO and catalytic poison from formic acid, an oxidation path not involving catalytic poison in the potential range from 0.5 V to 0.7 V is discussed in detail.     

Preparation and the physical/electrochemical properties of a Pt/C nanocatalyst stabilized by citric acid for polymer electrolyte fuel cells

Pt/C nanocatalysts were prepared by the reduction of chloroplatinic acid with sodium borohydride, with citric acid as a stabilizing agent in ammonium hydroxide solution. These nanocatalysts were obtained by altering the molar ratio of citric acid to chloroplatinic acid (CA/Pt) from 1:1, 2:1, 3:1 to 4:1. Transmission electron microscopy and X-ray diffraction analyses indicated that the well-dispersed Pt nanoparticles of around 3.82 nm in size were obtained when the CA/Pt ratio was maintained at 2:1. X-ray photoelectron spectroscopy measurements revealed that the 2:1, 3:1 and 4:1 molar ratio catalysts had a relatively higher amount of Pt in their metallic state than did the 1:1 molar ratio catalyst. Cyclic voltammetry results demonstrated that the Pt/C nanocatalysts annealed at 400 °C in an N₂ atm provided higher electrocatalytic activity. Among all the molar ratio catalysts, the 2:1 molar ratio catalyst exhibited the largest electrochemical active surface (EAS) area, and its methanol oxidation reaction current was superior to the E-TEK catalyst. The oxygen reduction reaction of the catalysts studied by linear sweep voltammetry and tested in a fuel cell indicated that the catalytic activity of the 2:1 molar ratio catalyst was comparable to that of an E-TEK catalyst.     

Effects of iron-tetrasulfophthalocyanine on the catalytic activities of Pt/C,PtRu/C,and Pd/C catalysts in a multi-anode direct formic acid fuel cell

This paper reports a systematic study of the effects of a promoter, iron-tetrasulfophthalocyanine (FeTSPc), on the catalytic activities of carbon supported Pt, PtRu, and Pd catalysts (Pt/C, PtRu/C, and Pd/C) for formic acid oxidation. A multi-anode direct formic acid fuel cell (DFAFC) was used to compare the effects on each catalyst of adding FeTSPc to the fuel stream. The FeTSPc significantly enhanced the activity of the Pt/C catalyst, but had little effect on the PtRu/C catalyst. The activity of the Pd/C catalyst was inhibited by the FeTSPc. A FeTSPc modified Pt/C was also evaluated in a conventional 5 cm² DFAFC.     

Pt–Sn/C electrocatalysts for methanol oxidation synthesized by reduction with formic acid

Carbon supported Pt–Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid, and their electrocatalytic activity for methanol oxidation was compared with commercial Pt/C and Pt₇₅Sn₂₅/C electrocatalysts. By X-ray diffraction analysis it was found that the Pt lattice parameter increases with the addition of Sn, indicative of alloy formation. It was confirmed that Sn exhibits cocatalytic activity for CO oxidation. The onset potential for the methanol oxidation reaction of the Pt–Sn electrode was approximately 0.1 V smaller than that on Pt both at room temperature and at 90 °C. The best performance in a direct methanol fuel cell was obtained using the Pt₇₅Sn₂₅/C alloy catalyst prepared by the formic acid method as the result of an optimal balance of Sn content, degree of alloying and metal particle size.     

Electrocatalytic oxidation of methanol and formic acid on dispersed electrodes: Pt, Pt–Sn and Pt/M(upd) in poly(2-hydroxy-3-aminophenazine)

Platinum particles dispersed in a poly(2-hydroxy-3-aminophenazine) film (pHAPh/Pt) provide a better catalyst than smooth Pt for the electrooxidation of methanol and formic acid in perchloric acid aqueous solutions. The catalytic activity of the Pt particles is further enhanced when Sn is codeposited in the polymer film. In the case of formic acid oxidation, the activity of Pt nanoparticles is influenced by adatoms of Tl, Pb and Bi deposited undepotential conditions. The upd-modified Pt particles are much more active than bare Pt particles. The morphology and identity of the metallic dispersion were examined by transmission electron microscopy.     

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.     

Pb and Sb modified Pt/C catalysts for direct formic acid fuel cells

PtPb/C and PtSb/C bi-metallic catalysts were synthesized by chemical deposition of Pb or Sb on a commercial 40% Pt/C catalyst. The performances of catalysts with a range of compositions were compared in a multi-anode direct formic acid fuel cell in order to optimize compositions and evaluate the statistical significance of differences between catalysts. The catalytic activity for formic acid oxidation increased approximately linearly with adatom coverage for both PtPb/C and PtSb/C, to maxima at fractional coverages of ca. 0.7. At a cell voltage of 0.5 V, the currents at the optimum Pb or Sb coverages were ca. 8 times higher than at unmodified Pt/C. CO-stripping results indicate that the presence of Pb or Sb facilitates the oxidation of adsorbed CO. In addition, both metals appear to produce electronic effects that inhibit poison formation on the modified Pt surface.     

Characterization and application of electrodeposited Pt, Pt/Pd, and Pd catalyst structures for direct formic acid micro fuel cells

In this work, we study the preparation, structural characterization, and electrocatalytic analysis of robust Pt and Pd-containing catalyst structures for silicon-based formic acid micro fuel cells. The catalyst structures studied were prepared and incorporated into the silicon fuel cells by a post CMOS-compatible process of electrodeposition, as opposed to the more common introduction of nanoparticle-based catalyst by ink painting. Robust, high surface area, catalyst structures consisting of pure Pt, pure Pd, and Pt/Pd = 1:1 were obtained. In addition, Pt/Pd catalyst structures were obtained via spontaneous deposition on the electrodeposited pure Pt structure. The catalyst structures were characterized electrochemically using cyclic voltammetry and chronoamperometry. All Pd-containing catalyst structures facilitate formic acid oxidation at the lower potentials and deliver higher oxidation currents compared to pure Pt catalyst structures. Fuel cells of these catalyst structures show that pure Pd catalyst structures on the anode exhibit the highest peak power density, i.e. as high as 28.0 mW/cm². The MEMS compatible way of catalyst electrodeposition and integration presented here has yielded catalyst structures that are highly active towards formic acid oxidation and are sufficiently robust to be compatible with post-CMOS processing.     

Methanol tolerant oxygen-reduction activity of carbon supported platinum–bismuth bimetallic nanoparticles

The oxygen reduction activity and methanol tolerance of Pt–Bi/C electrocatalysts were studied using electrochemical voltammetric techniques including rotating ring-disk electrode. The Pt–Bi/C catalyst was prepared via a polyol method and subjected to heat treatment to increase the degree of alloying. X-ray diffraction studies revealed the unalloyed character of the as-prepared catalyst and alloy formation upon heat treatment. The electrochemical behaviour of both catalysts showed different behaviour in dilute acid electrolytes, namely sulphuric and perchloric acids. In both electrolytes, the oxygen reduction reaction was found to occur via the four-electron process revealing that the mechanism of oxygen reduction is unaltered even in the presence of excess of methanol. Pt–Bi/C catalyst material showed dramatically different properties and reactivity with respect to oxygen reduction activity and methanol tolerance in perchloric and sulphuric acids. The onset potential for oxygen reduction reaction (ORR) significantly shifted by about 100 mV to more negative values and at the same time the current density was significantly enhanced. This type of non-ideal methanol-tolerant behaviour among Pt bimetallics and a “trade off” is common with all the known so-called methanol tolerant combinations of Pt. In general, the Pt–Bi surface appeared to have a negligibly lesser sensitivity towards methanol activity compared to pure platinum.     

Electrooxidation of formic acid on carbon supported PtxPd1−x (x = 0-1) nanocatalysts

In this work, carbon supported Pt_xPd_1−x (x = 0-1) nanocatalysts were investigated for formic acid oxidation. These catalysts were synthesized by a surfactant-stabilized method with 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as the stabilizer. They show better Pt/Pd dispersion and higher catalytic performance than the corresponding commercial catalysts. Furthermore, the electrocatalytic properties of Pt_xPd_1−x/C were found to depend strongly on the Pt/Pd deposition sequence and on the Pt/Pd atomic ratio. At a lower potential, formic acid oxidation current on co-deposited Pt_xPd_1−x/C catalysts increase with increasing Pd surface concentration. Nanoscale Pd/C is a promising formic acid oxidation catalyst candidate for the direct formic acid fuel cell.     

Sonochemical synthesis of Pt-doped Pd nanoparticles with enhanced electrocatalytic activity for formic acid oxidation reaction

Pt-doped Pd nanoparticle catalysts (Pd _n Pt, n is 12, 15 and 19) supported on carbon were synthesized by an ultrasound assisted polyol method. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The electrochemical activity of the electrocatalysts was investigated in terms of formic acid oxidation reaction (FAOR) at low concentration of formic acid in 0.1 M perchloric acid at room temperature. Formic acid oxidation on the Pd _n Pt/C commences at lower potential than a commercial Pt/C. Pd₁₉Pt/C catalyst showed the highest catalytic activity in FAOR compared to that of other catalysts. The obtained electrochemical results from voltammograms indicate that Pt-doped Pd catalysts can be a promising candidate for the anode material in direct formic acid fuel cells. The synthesis procedure is not only a very facile route but also a mass producible method for preparing carbon supported alloy nanoparticles.     

Enhanced activity of PtSn/C anodic electrocatalyst prepared by formic acid reduction for direct ethanol fuel cells

The Pt₃Sn/C catalyst with high electrochemical activity was synthesized under optimizing preparation conditions. The surface of carbon support pretreated by strong acid contains many O-H and CO groups, which will increase the active sites of PtSn/C catalysts. The catalyst structure was characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and temperature programmed reduction (TPR). The co-reduction of Pt⁴⁺ and Sn²⁺ ions causes Sn to enter Pt crystal lattice to form PtSn alloy whose surface, however, contains tin oxides with Sn⁴⁺ and Sn²⁺ valences, which can promote the ethanol oxidation. The crystallinity of PtSn decreases with the reduction of the atomic ratio of Pt:Sn. By prolonging the reaction time of formic acid, the forward anodic peak current of ethanol oxidation reaches 16.2 mA on the Pt₃Sn/C catalyst with 0.025 mg Pt loading.     

Electrochemical characterization of the electrooxidation of methanol,ethanol and formic acid on Pt/C and PtRu/C electrodes

Methanol, ethanol and formic acid electrooxidations in acid medium on Pt/C and PtRu/C catalysts were investigated. The catalysts were prepared by a microwave-assisted polyol process. Cyclic voltammetry and chronoamperometry were employed to provide quantitative and qualitative information on the kinetics of methanol, ethanol and formic acid oxidations. The PtRu/C catalyst showed higher anodic current densities than the Pt/C catalyst and the addition of Ru reduced the poisoning effect.     

Alternative platinum electrocatalyst supporter with micro/nanostructured polyaniline for direct methanol fuel cell applications

In this study, a series of micro/nanostructured polyanilines were synthesized and their morphology-dependent electrochemical properties for acting as a catalyst supporter for direct methanol fuel cell (DMFC) applications were investigated. These micro/nanostructures include submicron spheres, hollow microspheres, nanotubes, and nanofibers. Among the four micro/nanostructures, polyaniline nanofibers (PANF) manifest their superiority in high electrochemical active surface. Accordingly, PANF is adopted as the catalyst supporter thereafter. To couple with the use of the alternative catalyst supporter, this study also investigates the effect of reductant type on morphology and electrocatalytic properties of the PANF-supported Pt particles through a chemical reduction reaction. TEM images indicate that formic acid as a reductant results in well-dispersed Pt particles on the PANF surface. On the other hand, aggregations of Pt are observable when NaBH₄ is selected as a reductant. Moreover, the methanol oxidation current density measured with the Pt/PANF electrode being prepared by using formic acid is double that by using NaBH₄. Compared with Pt/XC-72, the Pt/PANF electrode possesses higher electrocatalytic activity and exhibits double power density. Moreover, Pt/PANF is superior to Pt/XC-72 in the aspect of operation stability based on a continuous discharge for 5 h.     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.