H(2)-air polymer-electrolyte-membrane fuel cells are electrochemical power generators with potential vehicle propulsion applications. To help reduce their cost and encourage widespread use, research has focused on replacing the expensive Pt-based electrocatalysts in polymer-electrolyte-membrane fuel cells with a lower-cost alternative. Fe-based cathode catalysts are promising contenders, but their power density has been low compared with Pt-based cathodes, largely due to poor mass-transport properties. Here we report an iron-acetate/phenanthroline/zeolitic-imidazolate-framework-derived electrocatalyst with increased volumetric activity and enhanced mass-transport properties. The zeolitic-imidazolate-framework serves as a microporous host for phenanthroline and ferrous acetate to form a catalyst precursor that is subsequently heat treated. A cathode made with the best electrocatalyst from this work, tested in H(2)-O(2,) has a power density of 0.75 W cm(-2) at 0.6 V, a meaningful voltage for polymer-electrolyte-membrane fuel cells operation, comparable with that of a commercial Pt-based cathode tested under identical conditions.

Size-controllable tin oxide nanoparticles are prepared by heating ethylene glycol solutions containing SnCl 2 at atmospheric pressure. The particles were characterized by means of transmission electron microscopic (TEM), X-ray diffraction (XRD) studies. TEM micrographs show that the obtained material are spherical nanoparticles, the size and size distribution of which depends on the initial experimental conditions of pH value, reaction time, water concentration, and tin precursor concentration. The XRD pattern result shows that the obtained powder is SnO 2 with tetragonal crystalline structure. On the basis of UV/vis and FTIR characterization, the formation mechanism of SnO 2 nanoparticles is deduced. Moreover, the SnO 2 nanoparticles were employed to synthesize carbon-supported PtSnO 2 catalyst, and it exhibits surprisingly high promoting catalytic activity for ethanol electrooxidation.

Hydrogen-air polymer-electrolyte-membrane fuel cells (PEMFCs) show promise for the replacement of gasoline internal-combustion engines for vehicle propulsion and other applications. However, the high cost of components, which is largely due to the use of platinum-based catalysts for the O 2reduction reaction (ORR), remains an impediment. [1] For a production of 500 000 PEMFC stacks a year, electrocatalysts alone were estimated to account for nearly half the cost of a stack. [2] Recent studies on pyrolyzed Fe/nitrogen/carbon and Co/ nitrogen/carbon catalysts for the ORR have increased their initial performance close to the level reached by platinumbased catalysts, and other studies have demonstrated promising durability. [3] We reported the use of a Zn II zeolitic imidazolate framework (ZIF) as a microporous support for ferrous acetate (Fe II Ac 2 ) and 1,10-phenanthroline to prepare a catalyst precursor which, after pyrolysis in Ar and then in NH 3 , resulted in unprecedented activity and power performance. [4] The investigated ZIF, referred to as ZIF-8, was a commercial product (Basolite Z1200 from BASF). ZIFs are a subclass of metal-organic frameworks (MOFs), which were first used for the preparation of platinum-free catalysts by Liu and co-workers. [5] MOFs are now actively investigated for electrochemical applications. [6] Herein, we describe our investigations on the replacement of 1,10-phenanthroline (phen) with 2,4,6-tris(2-pyridyl)-striazine (TPTZ) in our synthesis with ZIF-8. The use of TPTZ was investigated previously by Zhang and co-workers, who used a high-surface-area carbon material as a host. [7] However, the current density in the resulting PEMFC was only approximately 0.1 A cm À2 at 0.6 V, [7c] as compared to the value of 1.2 A cm À2 observed with Fe/phen/ZIF-8 precursors. [4] We show herein that a high performance can also be reached with TPTZ by the use of an appropriate synthesis procedure based on an improved understanding of the coordination chemistry of the Fe II /ligand/ZIF-8 catalyst precursor.We first prepared an Fe/TPTZ/ZIF-8 catalyst precursor of weight composition 1:10:90 (see the Supporting Information) by wet impregnation followed by drying and planetary ball milling. This composition results in a TPTZ/Fe molar ratio of about 2:1. The blue color characteristic of [Fe II (TPTZ) 2 ] was immediately observed when Fe II Ac 2 and TPTZ were dissolved. ZIF-8 was then dispersed in the solution, whose color slowly changed to gray-blue and then ochre. The absorption peak at 596 nm characteristic of [Fe II (TPTZ) 2 ] [8] was no longer observed in the UV/Vis spectrum after 2 h (Figure 1 a). Thus, [Fe(TPTZ) 2 ] had reacted with ZIF-8. We expected 2methyl-imidazole (2-MeIm), the structuring ligand of ZIF-8, to compete with TPTZ for ferrous cations. Indeed, the absorption peak of [Fe(TPTZ) 2 ] also vanished after the addition of 2-MeIm (see Figure S1 in the Supporting Information). In contrast, this competition for Fe II cations between 2-MeIm of ZIF-8 and the phen ligand was not observed for th...

In light of the debate about the role of the transition metal in non-precious metal catalysts (NPMCs), two different NPMCs, CN x and FeNC, were compared for activity towards oxygen reduction in acidic media and characterized using various techniques, including X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES), Extended X-ray absorption fine structure (EXAFS), Superconducting quantum interference device (SQUID) magnetometry, inductive-couple plasma optical emission spectrometry (ICP-OES) and temperature-programmed oxidation (TPO). The effect of acid washing as well as longterm exposure to fuel cell and half-cell environment on both catalysts was also studied. Although FeNC exhibited a much higher initial activity than CN x , it was seen to degrade rapidly in both half-cell and fuel cell environments, while CN x retained much of its initial activity. The results discussed are sought to clarify some of the ambiguity in the role of the transition metal in these two catalysts, and help establish that they are indeed two different materials with different active sites that catalyze ORR.