Nanostructured PdRu/C catalysts for formic acid oxidation

Pd and bimetallic PdRu nanoparticles supported on Vulcan XC-72 carbon prepared by the microwave-assisted polyol process are examined as electrocatalysts for the electrooxidation of formic acid. The catalysts are characterized by transmission electron microscopy and X-ray diffraction. The Pd and PdRu nanoparticles with sizes of <10 nm display the characteristic diffraction peaks of a Pd face-centered cubic (fcc) crystal structure. It is found that the addition of Ru to Pd/C can decrease the lattice parameter of Pd (fcc) crystal. The electrocatalytic activities of the catalysts are evaluated in sulfuric acid solution containing 1 M formic acid using linear sweeping voltammetry and chronoamperometry. The results show that Pd₅Ru₁/C displays the best electrocatalytic performance among all catalysts for formic acid electrooxidation.     

A spin-coated TiOx/Pt nanolayered anodic catalyst for the direct formic acid fuel cells

The CO poisoning of the platinum anodic catalyst which typically functions the catalytic deterioration of the direct formic acid fuel cells could be minimized with a simple modification for Pt with titanium oxide. The fabrication scheme involved the spin-coating of a Ti precursor onto a Pt thin layer that was physically sputtered onto a Si substrate. The whole assembly was subjected to a post-annealing processing to produce the TiOx layer (60 nm) in a porous structure (mostly Anatase) atop of the Pt surface. The porous nature of the TiOx layer permitted the participation of Pt in the electrocatalysis of the formic acid electro–oxidation (FAO). The annealing temperature was critical in identifying the catalytic efficiency and durability of the catalyst toward the FAO. Interestingly, if compared to bare-Pt substrates, the TiOx-modified catalysts could successfully steer the FAO toward the direct dehydrogenation (favorable and less energetic) pathway with more than an order of magnitude increase in the catalytic activity. It also provided a great opportunity for the mitigation of poisoning CO; concurrently with a lowering (~0.3 V) in the onset potential of the FAO. The scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction spectroscopy (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were all combined to evaluate, respectively, the catalyst’s morphology, composition, crystal structure and activity and further to understand the role of the TiOx in the catalytic enhancement.     

Nanostructured cathodic catalysts for direct methanol fuel cells

The high activity of catalysts based of nanodisperse Pt-P system and their tolerance to the poisoning effect of methanol are demonstrated for the working potentials of cathodes in methanol-air fuel cells. The catalysts’ activity in the oxygen reduction reaction in the presence of methanol is nearly hundred times that of catalysts based on mixed metal-chalcogenide systems.     

Influence of bi modification of pt anode catalyst in direct formic acid fuel cells

The influence of Bi modification of Pt anode catalyst on the performance of direct formic acid fuel cells was investigated. Compared with the unmodified Pt anode, the Bi modified Pt (PtBi(m)) electrode prepared by under-potential deposition (UPD) caused faster electrocatalytic oxidation of formic acid at the same value of the overpotential, and thus, PtBi(m) resulted in an increase in the power performance of direct formic acid fuel cells. Electrochemical impedance spectra helped to explain the difference of performance between the unmodified Pt and Bi modified Pt electrodes. Solution conductivity and dehydration phenomena occurring in highly concentrated formic acid solutions can also explain the higher power performance of PtBi(m).     

FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell

Fe_xC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell was investigated for the first time. The resultant Pt/Fe_xC–C catalysts were prepared by using a simple reduction reaction to load Pt on Fe_xC–C hybrid material, which was synthesized through the carbonization of sucrose and Fe(NO₃)₃. It was found that the Pt/Fe_xC–C catalysts exhibited excellent catalytic activity for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the fact that Fe_xC–C hybrid material ameliorated the tolerance to CO adsorption of Pt and facilitated the uniform dispersion of Pt.     

High-efficiency palladium catalysts supported on ppy-modified C60 for formic acid oxidation

A facile preparation of polypyrrole-modified fullerene supported Pd nanoparticles catalyst is introduced; electrochemical measurements demonstrate that the obtained Pd/ppy-C(60) catalyst shows a good electrocatalytic activity and stability for the oxidation of formic acid.     

Synthesis of Pd/C catalysts with designed lattice constants for the electro-oxidation of formic acid

Pd/C catalysts with designed lattice constants were synthesized for the electro-oxidation of formic acid. By changing the solvents in the preparation procedure, it was demonstrated that the different lattice constants of Pd crystallites could be controlled as desired. The varied lattice constants may be attributed to the difference in the interactions between solvents and PdCl₂. It was found that the lattice constant had an obvious effect on the electro-catalytic performance of Pd.     

Modification of palladium-based catalysts by chalcogenes for direct methanol fuel cells

Palladium-based catalysts, such as PdS_x/C and PdSe_x/C, have been developed as oxygen reduction catalysts for direct methanol fuel cells. Pd/C catalysts containing chalcogens have been synthesized and tested for oxygen reduction and the results have been analyzed based on changes in the palladium phase. Selenium addition to the catalyst promotes the oxygen reduction due to the modification of the palladium surface. However, sulfur reduces the oxygen reduction activity to a great extent as a result of semi-amorphous palladium phase formation. Both PdS_x/C and PdSe_x/C are highly methanol tolerant.     

Highly stable PtRuTiOx/C anode electrocatalyst for direct methanol fuel cells

In the present investigation, PtRuTiO_x/C electrocatalyst was prepared by a modified polyol synthesis method and the as-prepared electrocatalyst was treated under the reductive atmosphere (30 vol% H₂ in Ar) at 500 °C for 2 h (denoted as PtRuTiO_x/C-500) to enhance the interaction between the metal particles and the support. For comparison, the commercial PtRu/C electrocatalyst was also treated by the same procedure as PtRuTiO_x/C (denoted as PtRu/C-500). Transmission electron microscopy results indicated that PtRuTiO_x/C electrocatalyst exhibited not only a uniform dispersion and narrow size distribution with a smaller particle size, but also excellent stability during the thermal treatment. In contrast, the commercial PtRu/C electrocatalyst is not stable during the thermal treatment and the metal particles greatly agglomerated. The results of CO-stripping voltammetry, single direct methanol fuel cell tests and life-time test jointly showed that PtRuTiO_x/C-500 had better durability than commercial PtRu/C while keeping a desirable activity toward methanol electro-oxidation, which may be attributed to the addition of titanium oxide that improved the interaction between noble metal particles and the support.     

Optimization of a permeation-based microfluidic direct formic acid fuel cell (DFAFC)

A design for a passive, air-breathing microfluidic fuel cell utilizing formic acid (FA) as a fuel is described and its performance characterized. The fuel cell integrates high surface area platinum (cathode) and palladium-platinum (anode) alloy electrodes within a PDMS microfluidic network that keeps them fully immersed in a liquid electrolyte. The polymer network that comprises the device also serves as a self-supporting membrane through which FA and oxygen are supplied to the alloy anode and cathode, respectively, by passive permeation from external sources. The cell is based on a planar form-factor and in its operation exploits FA concentration gradients that form across the PDMS membrane. These latter gradients allow the device to operate stably, producing a nearly constant limiting power density of ~0.2 mW/cm2, without driven laminar flow of fluids or the incorporation of an in-channel separator between the anodic and the cathodic compartments. The power output of this elementary device in air is subject to electrolyte mass transport impacts, which can be reduced for a given design rule by decreasing the internal ohmic resistance of the cell. The results suggest that operational stability can be improved by decreasing the kinetic losses imposed on the cathode side of the cell due to FA crossover and modalities for doing so, such as by increasing the efficiency of fuel capture at the anode.     

Microstructural and metal-support interactions of the Pt-CeO2/C catalysts for direct methanol fuel cell application

To understand the ceria promotion effect of Pt-CeO(2)/C catalysts on methanol oxidation, microstructural and metal-oxide interactions of Pt-CeO(2)/C catalysts with an atomic ratio of Pt/Ce between 0.14 and 1.4 were systematically examined using high-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS). With an increasing Pt content in the catalysts, Pt particles gradually invaded into the ceria supports and decoration on Pt particles was observed. Simultaneously, the morphology of the supports was dramatically modified with nanocrystalline and amorphous ceria formed between and/or around the Pt particles. It reveals that the Pt-ceria interaction could take place in the catalysts and the influence of the interaction was enhanced with an increasing Pt/Ce ratio. The EELS study demonstrated that the strong Pt-ceria interaction was related to the redox reaction between Pt and ceria. Experimental results also suggested that the strong interaction between Pt and ceria could contribute to the promotion effect of ceria on the oxidation of methanol.     

Sustainable energy: a review of formic acid electrochemical fuel cells

Of the many candidate fuels for low-temperature fuel cells, one of the most promising is formic acid. Although it has been investigated as such for nearly 50 years, rapid advances in recent times have begun to release the potential for formic acid fuel cells as high-performance, portable fuel cells with some products about to reach the market. In this review, we briefly summarise the recent advances in formic acid fuel cells.     

Carbon-supported PdSn nanoparticles as catalysts for formic acid oxidation

Pd and PdSn nanoparticles supported on Vulcan XC-72 carbon are prepared by a microwave-assisted polyol process. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), linear sweeping voltammetry, and chronoamperometry. The results show that the Pd and PdSn nanoparticles, which are uniformly dispersed on carbon, are 2–10 nm in diameters. All Pd/C and PdSn/C catalysts display the characteristic diffraction peaks of a Pd face-centered cubic (fcc) crystal structure. It is found that the addition of Sn to Pd can increase the lattice parameter of Pd (fcc) crystal. The PdSn/C catalysts have higher electrocatalytic activity for formic acid oxidation than a comparative Pd/C catalyst and show great potential as less expensive electrocatalyst for formic acid electrooxidation in DFAFCs.     

Tolerant cathode catalysts for direct methanol fuel cell

Effect of methanol on the reduction kinetics of oxygen on highly dispersed catalysts 60Pt/C (HiSPEC 9100), 40Pt/carbon nanotubes, and CoFe/carbon nanotubes for the cathode of a direct methanol-oxygen fuel cell was studied. It was shown that the CoFe/carbon nanotubes catalyst surpasses the platinum systems in tolerance to the alcohol. It was found that the tolerance of the cathode catalyst strongly affects the current–voltage characteristics of the fuel cell, which is the principal result of the study and constitutes its scientific novelty. The maximum power density of an alkaline methanol-oxygen fuel cell with nonplatinum cathode (260 mW cm^–2) exceeds the characteristics of similar fuel cells with platinum cathode catalysts, both obtained in the present study and described in the literature, which points to the practical importance of the study.     

Carbon-supported palladium catalysts for fuel cells

Small controlled amounts of palladium were electrochemically deposited onto various carbon supports from solutions of glycinate-chloride complexes of palladium(II) in order to obtain palladium catalysts suitable for use in fuel cells. The catalytic activity of the resulting catalytic layers was studied in reactions of reduction of atmospheric oxygen and oxidation of methanol and ethanol in acid and alkaline media by measuring cyclic voltammetric curves on a rotating disk electrode.     

Carbon-supported IrSn catalysts for a direct ethanol fuel cell

Carbon-supported Ir₃Sn/C and Ir/C catalysts were simply prepared with NaBH₄ as a reducing agent under the protection of ethylene glycol at room temperature. TEM and X-ray diffraction (XRD) data showed that the catalysts with small particle size exhibited the typical characteristic of a crystalline Ir fcc structure. Their electro-catalytic activities in comparison with Pt/C and Pt₃Sn/C catalysts also prepared by the NaBH₄ reduction process were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) techniques. The results indicated that Ir-based catalysts showed superior electro-catalytic activity towards ethanol oxidation to Pt/C and Pt₃Sn/C catalysts, mainly at low potential region. During single-cell tests at 90 °C, better performances of Ir-based catalysts as anodes were obtained compared to that of Pt/C catalyst. The comparable overall performance of Ir₃Sn/C to Pt₃Sn/C makes it a promising alternative choice of anode catalyst for direct ethanol fuel cells.