F2-Fluorination of Fe/N/C catalysts poisons FeN4, but not CNx sites. Main causes of instability in PEMFCs are either FeN4 demetalation for Fe/N/C or H2O2 when FeN4 sites are poisoned by fluorination or absent as in MOF_CNx_Ar + NH3.

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Nitrogen and phosphorus-codoped graphene dots supported on nitrogen-doped three-dimensional graphene (N, P-GDs/N-3DG) have been synthesized by a facile freeze-annealing process. On the surface of the 3D interconnected porous structure, the N, P-GDs are uniformly dispersed. The as-prepared N, P-GDs/ N-3DG material served as a metal-free catalyst for oxygen reduction reaction (ORR) in an alkaline medium and evaluated by a rotating ring-disk electrode. The N, P-GDs/N-3DG catalyst exhibits excellent ORR activity, which is comparable to that of the commercial Pt/C catalyst. Furthermore, it exhibits a higher tolerance to methanol and better stability than the Pt/C. This enhanced electrochemical catalytic performance can be ascribed to the presence of abundant functional groups and edge defects. This study indicates that P−N bonded structures play a vital role as the active sites in ORR.

Two types of FeN 4 -based catalytic sites have been proposed in the literature to perform the oxygen reduction reaction (ORR) in PEM fuel cells running with a Fe-based catalyst. They are FeN 4 /C, derived from the molecular structure of iron porphyrin, and FeN (2+2) /C, derived from the structure of the iron complex with two 1,10-phenanthroline molecules. The energetics and thermodynamic stability (equilibrium constant, K c , for iron acid leaching at pH ∼ 0) of these two types of sites were determined and were already reported in this journal [J. Electrochem. Soc., 164(9) F948-F957 ( 2017)]. This work deals with the same FeN 4 sites but this time after their fluorination on the central Fe atom and on their carbon support. All evaluated fluorinated FeN 4 -based sites are stable at both 298 and 353 K, especially F-FeN 4 /C(F) and F 2 -FeN (2+2) /C(F). Interatomic d Fe−N , d Fe−F , and bond energies E Fe−F derived in the frame of the thermodynamic calculations were compared with the values obtained by density functional theory (DFT) calculations, and an agreement was found. DFT was also used to assess the ORR capability of both F-FeN 4 /C and F-FeN (2+2) /C. Both fluorinated sites were found to be ORR active when O 2 was bonded to the free side of the Fe atom, opposite to the F atom.

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Nowadays, the availability of the vehicle position gets more and more important. The use of the Global Positioning System (GPS) receiver has solved this problem. Nevertheless, this system could suffer from availability of the minimum number of visible satellite, especially in harsh environment. Thus, complementary system, such us Inertial Navigation System (INS) comes to help the GPS in order to guarantee the availability of the position in these environments. Nevertheless, low cost Microelectromechanical System (MEMS) based INS integrated with the GPS has shown weak performances even in case of using Kalman filtering. To deal with this problem, this paper proposes a new approach based on loosely coupled GPS/INS integration using Extended Kalman Filter (EKF) and aided by a map matching technique. In the literature, researchers have widely investigated the EKF in order to improve the position accuracy. The developed approach overcomes the drawback of this method by adding the Snap To Road (STR) as a map matching technique. Experimental tests of EKF aided by STR system have shown better performances than standalone EKF even in harsh environment.

We present a theoretical study of the optical response of silver clusters, Ag n , where n = 4, 8, 10, 20, complexed with the aryl thiols FC 6 H 4 S − and CH 3 C 6 H 4 S − in an aqueous solution. The absorption spectra are found to be strongly modified by the adsorption of aromatic thiols with a red shift of the plasmon-like band and the emergence of new excitations due to charge-transfer transitions between thiols and the metal cluster. Our results highlight the influence of the molecular orientation of thiol ligands relative to the cluster surface on the excitations. We also analyze the appropriateness of substituting a thiol molecule by a SH group. Calculations have been performed using the time-dependent densityfunctional theory (TDDFT). ■ INTRODUCTIONThe interaction between light and metal nanoparticles is a topic of great fundamental and technological interest with potential applications in many fields, such as nanoelectronics, nanooptics, and biosciences. 1 In particular, the noble metal nanoparticles are characterized by their ability to support surface plasmons. However, their optical properties depend, among others, on the particle's shape 2−5 and the particle's size. 6−15 For example, small silver clusters have molecular-like optical transitions, and their spectra are composed from several narrow or broad peaks whose the positions depend on the number of atoms that compose the cluster. 8,16−18 As silver clusters grow, they lose these molecular properties and develop a large, unique absorption band in the UV−vis region. The emergence of this plasmon-like band has been shown to occur for clusters of about 20 silver atoms. 12,19 The plasmon band is red shifted as the cluster's size increases. 6,7,9,20,21 While medium-sized clusters (several tens of atoms) present a main band near 4 eV; 8,9,22,23 the nanoparticles of about 8 nm in diameter show a strong optical absorption band near 3.2 eV. 7,21 Let us note that the optical properties can be also modified by mixing several elements together. 23−27 Large efforts are engaged in the synthesis methods in order to control the size, shape, and atomic arrangement of metal nanoparticles, on which depend their physical and chemical properties. As free metal nanoparticles are inherently unstable against thermal and chemical decomposition, one had to develop techniques to stabilize them. When metal clusters are produced in the gas phase, they can be accumulated and stabilized in a protective solid matrix. 8,18,28 If they are synthesized in solution, the stabilization of clusters may be ensured by the surface adsorption of strong ligands, like thiols, resulting in thiolate monolayer-protected clusters, consisting of a metallic core that is surrounded by ligands. 29−34 The adsorbed molecules provide original and controllable properties to the clusters, mainly in the field of optical absorption or emission, and enable chemical functionalization. However, the optical properties of metal nanoparticles can be affected by the adsorbate. 14,29,35−37 The plasmon resonances o...

Fluorination is considered as a means of reducing the degradation of Fe/N/C, a highly active FeNx-doped disorganized carbon catalyst for the oxygen reduction reaction (ORR) in PEM fuel cells. Our recent experiments have, however, revealed that fluorination poisons the FeNx moiety of the Fe/N/C catalytic site, considerably reducing the activity of the resulting catalyst to that of carbon only doped with nitrogen. Using the density functional theory (DFT), we clarify in this work the mechanisms by which fluorine interacts with the catalyst. We studied 10 possible FeNx site configurations as well as 2 metal-free sites in the absence or presence of fluorine molecules and atoms. When the FeNx moiety is located on a single graphene layer accessible on both sides, we found that fluorine binds strongly to Fe but that two F atoms, one on each side of the FeNx plane, are necessary to completely inhibit the catalytic activity of the FeNx sites. When considering the more realistic model of a stack of graphene layers, only one F atom is needed to poison the FeNx moiety on the top layer since ORR hardly takes place between carbon layers. We also found that metal-free catalytic N-sites are immune to poisoning by fluorination, in accordance with our experiments. Finally, we explain how most of the catalytic activity can be recovered by heating to 900 °C after fluorination. This research helps to clarify the role of metallic sites compared to non-metallic ones upon the fluorination of FeNx-doped disorganized carbon catalysts.