Search

Abstract: In this paper, the reversible and the irreversible loss in performance of direct methanol fuel cell (DMFC) single cells induced by freeze/thaw cycling are determined and discussed. The reversible loss in performance is attributed to the decreased activity of electrocatalysts due to the strong adsorption of the intermediates from methanol electro-oxidation at subzero temperatures, while the irreversible loss in performance is due to the damage of membrane electrode assembly (MEA) structure. It is found that the reversible degradation of performance is dominant when the cell operated at low current densities with O2; the irreversible degradation is more obvious when the cell discharged at high current densities or operated with air. A method, applying a reverse current on the single cell, is put forward to recover the reversible loss in performance. By this method, the voltage of the single cell operated with O2 at 100 mA cm−2 drops only about 16 mV after experiencing 100 freeze/thaw cycles between−10 and 60 °C. [Copyright &y& Elsevier]

Abstract: A graphitic mesoporous carbon (denoted as GMC) was synthesized using resorcinol and formaldehyde as carbon precursors and iron nitrate as a graphitization catalyst. The GMC was characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and nitrogen adsorption. The results show that the GMC has a mesoporous structure and a high surface area of 403 m2 g−1, and particularly, a well-defined graphitic framework. Using the GMC as the support, a PtRu/GMC was synthesized to act as an electrocatalyst for the methanol oxidation reaction (MOR). A counterpart with Vulcan® XC-72 (denoted as XC) as the support was prepared for comparison. TEM images show that PtRu nanoparticles are distributed uniformly on the carbon supports for both electrocatalysts. The electrochemical activity of the PtRu/GMC toward the MOR is slightly higher than that of the PtRu/XC in both half cell and single cell measurements. The 1500h stability test of a single cell suggests that the PtRu/GMC is excellent stable. [Copyright &y& Elsevier]

Abstract: A carbon supported PtNi/C electrocatalyst synthesized via a polyol process was characterized by XRD, TEM and voltammetry techniques. The XRD analysis showed a decreased lattice constant of Pt for the PtNi/C catalyst compared with the Pt/C, indicating partial PtNi alloy formed. The PtNi/C exhibited enhanced mass activity towards methanol oxidation reaction as well as decreased CO stripping currents in alkaline media compared with the Pt/C. Density functional theory studies revealed the electronic structure modification of Pt by Ni atoms and weakened CO adsorption energy on the Pt3Ni than on the Pt4 clusters, which may account for the increased MOR activity. [ABSTRACT FROM AUTHOR]

• Ultrathin 2D metal-organic frameworks decorated with Pt NPs have been fabricated using an ultrasonication-assisted method. • A "win-win" electron decoration effect has been evidenced on the active sites for both ORR and OER. • Remarkable bifunctional catalytic activity towards ORR and OER with ultralow overpotential gap of 665 mV has been demonstrated. • Excellent performance and durability is achieved in the rechargeable Zinc-air battery assembled with the bifunctional catalyst. To meet the increasing demands for highly active electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), here in this work, a new strategy of synergistic nano-architecture design based on Platinum nanoparticles (Pt NPs) and ultrathin two-dimensional (2D) metal-organic frameworks (MOFs) is developed for bifunctional electrochemical catalysts. Compared with commercial Pt/C and RuO 2 catalysts, remarkable enhancements in activity and durability of both oxygen reduction and oxygen evolution reactions are achieved on our PtNPs@MOFs composite materials, with one of the lowest over-potential gaps (E gap) of 665 mV that has ever been reported. The tests on the assembled Zn-air batteries have revealed promising electrocatalytic performance and practical advantage of our new materials as air cathode catalyst. Both experimental results and theoretical study have confirmed the synergistic effect between Pt NPs and MOF nanosheets through a "win-win" electron structural modification, demonstrating the effectiveness of our strategy in developing effective bifunctional oxygen electrocatalysts for various types of electrochemical devices. [ABSTRACT FROM AUTHOR]

Abstract: Carbon-supported bimetallic PdAg catalysts with Pd/Ag atomic ratios varying from 4/1 to 1/2 were prepared by an impregnation–reduction method. The impregnated black mixture was treated in H2/N2 atmosphere at a temperature varying from 180 to 500°C. The obtained Pd x Ag y /C catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA). XRD results show that the lattice constant of Pd is dilated, suggesting the formation of PdAg alloy. The lattice constant of Pd for the Pd x Ag y /C-500 (reduced at 500°C by H2) increases linearly and the average metal particle size decreases slightly from 6.8 to 5.1nm with increasing Ag fractions from 20% to 67% in the PdAg composition. For Pd x Ag y /C catalysts with a certain specific Pd/Ag atomic ratio, e.g., Pd2Ag1/C, the dilated lattice constant of Pd is independent of the reducing temperature, indicating the alloy degree for the Pd2Ag1/C-t catalysts is comparable. The average metal particle size for the Pd2Ag1/C-t catalysts increases from 3.4 to 5.2nm with H2 reduction temperature increasing from 180 to 500°C. The potentiodynamic measurements on ethanol electrooxidation reaction (EOR) show that the catalytic activities for the Pd x Ag y /C-t catalysts toward the EOR are improved by alloying Pd with Ag. At typical potential of a working fuel cell, e.g., −0.4V vs. Hg/HgO, the EOR current density presents a volcano shape as a function of the Ag fractions in PdAg with the maximum occurs at the Pd/Ag atomic ratios between 2/1 and 3/1. The CA tests show that the Pd x Ag y /C-500 catalysts perform high stability than that of Pd/C-500. The improved EOR activity for the Pd x Ag y /C-t catalysts, compared with whether Pd/C or Ag/C catalyst, may possibly be attributed to the formation of PdAg alloy and the fitted particle size. [Copyright &y& Elsevier]

Abstract: Carbon-supported bimetallic Pt m Pb1 (m =1, 2, 3) electrocatalysts with different Pt/Pb atomic ratios were synthesized by a polyol method. The X-ray diffraction results reveal that a PtPb alloy formed in the Pt m Pb1/C electrocatalysts. TEM images show that the PtPb nanoparticles distribute uniformly on the carbon support, and are about 4–5nm in size. The Pt m Pb1/C bimetallic catalysts show superior activities toward methanol electrooxidation reaction (MOR) than the Pt/C in alkaline media. Both CO stripping measurements and density functional theory studies reveal that CO adsorption decreased significantly on the Pt m Pb1/C bimetallic catalysts compared with on pure Pt, which may offer an explanation for the enhanced MOR activity of the Pt m Pb1/C bimetallic catalysts. [Copyright &y& Elsevier]