Fe-N-C catalysts are very promising materials for fuel cells and metal-air batteries.This work gives fundamental insights into the structural composition of an Fe-N-C catalyst and highlights the importance of an in-depth characterization. By nuclear-and electron-resonance techniques,weare able to show that even after mild pyrolysis and acid leaching, the catalyst contains considerable fractions of a-iron and, surprisingly,i ron oxide.O ur work makes it questionable to what extent FeN 4 sites can be present in Fe-N-C catalysts prepared by pyrolysis at 900 8 8Ca nd above.T he simulation of the iron partial density of phonon states enables the identification of three FeN 4 species in our catalyst, one of them comprising as ixfold coordination with end-on bonded oxygen as one of the axial ligands.
The performance of a cryogenically cooled double-crystal silicon monochromator was studied under high-heat-load conditions with total absorbed powers and power densities ranging from 8 to 780 W and from 8 to 240 W mm(-2), respectively. When the temperature of the first crystal is maintained close to the temperature of zero thermal expansion of silicon, the monochromator shows nearly ideal performance with a thermal slope error of 0.6 µrad. By tuning the size of the first slit, the regime of the ideal performance can be maintained over a wide range of heat loads, i.e. from power densities of 110 W mm(-2) (at total absorbed power of 510 W) to 240 W mm(-2) (at total absorbed power of 240 W).
Fe-N-C catalysts are very promising materials for fuel cells and metal-air batteries.This work gives fundamental insights into the structural composition of an Fe-N-C catalyst and highlights the importance of an in-depth characterization. By nuclear-and electron-resonance techniques,weare able to show that even after mild pyrolysis and acid leaching, the catalyst contains considerable fractions of a-iron and, surprisingly,i ron oxide.O ur work makes it questionable to what extent FeN 4 sites can be present in Fe-N-C catalysts prepared by pyrolysis at 900 8 8Ca nd above.T he simulation of the iron partial density of phonon states enables the identification of three FeN 4 species in our catalyst, one of them comprising as ixfold coordination with end-on bonded oxygen as one of the axial ligands.
A novel sample environment enabling optical pumpnuclear resonance probe experiments has been installed at the beamline P01, Petra III, DESY Hamburg. This set-up has been used to investigate optically induced spin state changes of spin crossover (SCO) complexes by nuclear resonant scattering immediately after excitation by an optical laser pulse. Here, we report the technical details as well as first results of experiments performed at 290 K and 80 K on the SCO complexes [Fe (NH2trz)3]Cl2 and [Fe(PM-BiA)2(NCS)2], respectively. The 57 Fe-enriched SCO complexes were excited by a 531 nm laser with a pulse length <100 ps. Evaluation of the nuclear forward scattering data clearly indicate the presence of high spin (HS) states when the complexes are excited by laser pulses and a pure low spin (LS) state in the absence of any laser pulse. Furthermore, the dependence of the optically excited HSfraction has been determined as a function of the average optical power.
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