Preparation of stoichiometric CuInS2 surfaces

Thin films of KCN etched CuInS2 surfaces during an annealing procedure are investigated by photoelectron spectroscopy and scanning electron microscopy, combined with energy dispersive X ray analysis. A significant deviation from stoichiometric composition and the formation of Cu poor phases after etching is well known. Because of the ternary system the polycrystalline absorber layer need to be characterised in terms of the CuInS2 monophase, homogeneous elemental distribution or the size of the polycrystalline grains. Here, we present the effect of a heat treatment of samples etched with KCN, a procedure, which leads ot surfaces of CuInS2 with almost ideal elemental compositio

On the structural composition and stability of Fe N C catalysts prepared by an intermediate acid leaching

The development of highly active and stable non noble metal catalysts NNMC for the oxygen reduction reaction ORR in proton exchange membrane fuel cells PEM FC becomes of importance in order to enable cost reduction. In this work, we discuss the structural composition as derived from Fe 57 Mö bauer spectroscopy and X ray dif fraction, catalytic performance determined by a rotating ring disk electrode RRDE technique and stability evaluation of our Fe N C catalysts prepared by an intermediate acid leaching IAL . The advantage of this IAL is given by a high density of active sites within the catalyst, as even without sulphur addition, an iron carbide formation and related disintegration of active sites are inhibited. In addition, our accelerated stress tests illustrate better stability of the sulphur free IAL catalyst in comparison to the sulphur added on

Effect of iron carbide formation on the number of active sites in Fe N C catalysts for the oxygen reduction reaction in acidic media

In this work Fe N C catalysts were prepared by the oxalate supported pyrolysis of FeTMPPCl or H2TMPP either in the presence or absence of sulfur. The well known enhancing effect of sulfur addition on the oxygen reduction activity was confirmed for these porphyrin precursors. The pyrolysis process was monitored in situ by high temperature X ray diffraction under synchrotron radiation HT XRD and thermogravimetry coupled with mass spectroscopy TG MS . It was found that the beneficial effect of sulfur could be attributed to the prevention of iron carbide formation during the heat treatment process. In the case of pyrolysis of the sulfur free precursors an excessive iron carbide formation leads to disintegration of FeN4 centers, hence limiting the number of ORR active sites on the final catalyst. Physical characterization of the catalysts by bulk elemental analysis, X ray diffraction XRD , Raman and 57Fe M o bauer spectroscopy confirmed the outcome from HT XRD and TG MS. It could be shown that the avoidance of carbide formation during pyrolysis represents a promising way to enhance the density of ORR active sites on those catalysts. This can be done either by sulfur addition or the performance of an intermediate acid leaching. As iron carbide is often found as a by product in the preparation of Fe N C catalysts this work gives some general strategies for enhancing the density of active sites enabling higher current densitie

High resolution surface analysis of Si roughening in dilute ammonium fluoride solution

The initial stages of porous Si formation on Si 111 in dilute ammonium fluoride solution are analysed by photoelectron spectroscopy PES using synchrotron radiation. PES in the por Si formation regime shows no contradiction to a recent dissolution model. The contribution from a Si 2p surface core level shift shows that 0.4 ML of the surface is still H terminated after interruption of the conditioning process at the first photocurrent maximum. A higher oxidised species found with EB 103.2 eV is attributed to a precipitate, expected from the reaction mechanism and from theoretical calculations using density functional theory DFT . The roughening upon por Si formation is monitored by in situ AFM measurements. A RMS roughness parameter of 2.6 nm is calculated