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Non-precious metal catalysts are well investigated in electrocatalysis. Fe and N co-doped carbon (Fe-N-C) catalysts have drawn great attention due to their low cost and good performance in the oxygen reduction reaction (ORR) and recently in the oxygen evolution reaction (OER). Based on the recent advances of a variety of physical characterization techniques, more information about the chemical environment of the catalytic active sites has been acquired. However, due to the complexity of the catalytic material and process, the real active structures are still controversial. In this work, several active sites are proposed for Fe-N-C catalysts (L-FeNx, x = 2 or 4, L = nothing, O or OH) and their performance in electrochemical ORR and the OER are investigated. The computations are based on density functional theory (DFT), including Van der Waals interaction and solvation effect with an implicit electrolyte model. Calculations indicate that the catalytic activity of the Fe centers depends strongly on the N coordination number and on the presence of extra ligands like OH group. In particular, HO-FeN2, but not FeN4, appears as the most active site. Scaling relations are obtained by connecting the free energy of potential-determining steps with the adsorption free energy of intermediates. Furthermore, three promising active sites suggested from scaling relations are studied by the more elaborate surface charging approach, which includes the influence of the applied potential and the electrolyte. The results show that the specific treatment of the influence of the applied potential has a minor influence at low potential, which is the case for the ORR, but a major influence at higher potential, as for the OER, changing the calculated overpotential by up to 0.34 V.

A novel method based on conversion of chlorinated volatile organic compounds (CVOCs) to chlorine using a new type of column packed with nanometer Ti[O.sub.2] coupled with chemiluminescence (CL) has been developed for determination of them in workplace air. CVOCs are converted to chlorine by nanometer Ti[O.sub.2] at 220[degrees]C. The [Cl.sub.2] that is produced is selectively enriched on the column and subsequently released from the column at 600[degrees]C. The [Cl.sub.2] that is released is determined using a postcolumn CL detector. The CL intensity was linear with C[Cl.sub.4] in the range of 0.1-380 ppm, and the detection limit was 40 ppb (S/N = 3). Higher sensitivity could be acquired by using a larger volume of enrichment. A similar procedure could be used for the determination of other CVOCs. CL intensities of C[H.sub.2][Cl.sub.2], CH[Cl.sub.3], and C[Cl.sub.4] at the same concentration increased in the order C[H.sub.2][Cl.sub.2] < CH[Cl.sub.3] < C[Cl.sub.4]. The method has been successfully applied to the determination of C[Cl.sub.4] in workplace air, where 0.15-150 ppm C[Cl.sub.4] would be detected. The possible mechanism for the long lifetime of the column packed with nanometer Ti[O.sub.2] was tested using Raman spectrometer, X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that the column packed with nanometer Ti[O.sub.2] could be operated in the reversible mode for determination of CVOCs under the present conditions. The method would be potentially applied to the analysis of other chlorinated compounds in environment, such as persistent organic pollutants.