A Combined Surface Science and Electrochemical Study of Tungsten Carbides as Anode Electrocatalysts

An effective anode electrocatalyst in direct methanol fuel cell (DMFC) should have high activity for the oxidation of methanol and the decomposition of water, while remaining stable under the relatively harsh anode environment. Although the Pt/Ru bimetallic alloy is currently the most effective anode electrocatalyst, both Pt and Ru are expensive due to limited supplies and both are susceptible to CO poisoning. Consequently, the discovery of less expensive and more CO tolerant alternatives to the Pt/Ru catalysts would help facilitate the commercialization of DMFC. In this paper we will discuss the possibility of using tungsten carbides (WC) and Pt-modified WC as potential anode electrocatalysts in DMFC. We will provide an overview of our recent work, using a combined approach of fundamental surface science studies and in-situ electrochemical evaluation of the activity and stability of tungsten carbides. We will demonstrate the feasibility to bridge fundamental surface science studies on single crystals with the electrochemical evaluation on polycrystalline WC films. We will also discuss the synergistic effect by supporting low coverages of Pt on the WC substrate to further enhance the electrochemical performance of WC.     

Lothar Collatz zum 60. Geburtstag

Ohne Zusammenfassung     

Untersuchungen über elektrische Gleitfunken

Zusammenfassung Die hier beschriebenen Gleitfunkenbilder kommen durch den im Funkenkanal auftretenden Gasdruck zustande. Die Breite der Störungszone nimmt bei konstanter Zündspannung mit zunehmender Gleitfunkenlänge ab, bei gleicher Bahnlänge mit zunehmender Zündspannung zu. Die Lage der-Zone fällt im allgemeinen mit der Winkelsymmetralen zusammen, jedoch zeigen sich bei den kleineren, hier untersuchten Zündspannungen Abweichungen von dieser Mittellage. Aus dieser Abweichung läßt sich der Wertc/v errechnen und auch die Richtung vonc, ob von der negativen zur positiven Elektrode oder umgekehrt, ermitteln. Der erstere Fall ist häufiger, jedoch tritt auch der zweite Fall auf. Es scheint, daß dabei Raumladungen eine ausschlaggebende Rolle spielen.     

Uptake of Cm(III) and Eu(III) by calcium silicate hydrates: a solution chemistry and time-resolved laser fluorescence spectroscopy study

The interaction of the two chemical homologues [Cm(III) and Eu(III)] with calcium silicate hydrates (CSH phases) at pH 13.3 has been investigated in batch-type sorption studies using Eu(III) and complemented with time-resolved laser fluorescence spectroscopy (TRLFS) using Cm(III). The sorption data for Eu(III) reveal fast sorption kinetics and a strong uptake by CSH phases with distribution ratios of (6 +/- 3) x 10(5) L kg(-1). Three different Cm(III) species have been identified: A nonfluorescing species, which was identified as a curium hydroxide (surface) precipitate, and two fluorescing Cm(III)/CSH-sorbed species. The fluorescing sorbed species have characteristic emission spectra with main peak maxima at 618.9 and 620.9 nm and fluorescence emission lifetimes of 289 +/- 11 and 1482 +/- 200 micros, respectively. From the fluorescence lifetimes, it was calculated that the two fluorescing Cm(III) species have one or two and no water molecules left in their first coordination sphere, suggesting that these species are incorporated into the CSH structure. A structural model for Cm(III) and Eu(III) incorporation into CSH phases is proposed based on the substitution for Ca at two different types of sites in the CSH structure.