SIMS methodology for probing the fate and dispersion of catalytically active molecules

Secondary ion mass spectrometry (SIMS) with 520 keV A u 400 4 + projectiles operating in event-by-event bombardment/detection mode was applied to investigate pyrolized mixtures of catalyst (vitamin B12) and carbon supports (carbon black). The specimens are alternative cathode materials to platinum for fuel cells. The goal was to understand the effect of temperature on the chemical environment of the catalytically active sites formed on the carbon supports during pyrolysis. The A u 400 4 + projectiles probed the samples one-at-a-time in a stochastic manner and the resulting secondary ions from the individual impacts were recorded separately. The coincidental methodology allows one to compile mass spectra comprising selectively the secondary ions from the impacts on the active sites, extracting the local molecular information of the active sites within a nanodomain (∼10 3 nm 3 ). The detection of CoN 4 C x − suggests Co-N 4 be the moiety retained from the pyrolized vitamin B12 in the presence of the carbon black. Variations in the local chemical environment of the active sites as a function of pyrolysis temperature were also observed. Additionally, we could quantify the dispersion of the active sites among the carbon supports, a measure providing a direction for future device optimization.