Oxygen reduction in acid media: influence of the activity of CoNPc(1,2) bilayer deposits in relation to their attachment to the carbon black support and role of surface groups as a function of heat treatment

O2 reduction was investigated using rotating disk electrode and voltammetry techniques on NPcCo(1,2) impregnations deposited onto two kinds of carbon black support. They were selected on the basis of their similar pH and dibuthylphthalate (DBP) adsorption values. Samples were also characterized by IR and X-ray photoelectron spectroscopy techniques. An optimized thermal treatment yielded an improvement in the O2 reducibility and identical activities (with N = 3.8) on both supports. These spectroscopic methods revealed a bilayer structure and suggested the presence of two sorts of site (active and inactive) which differed in their attachment of the substrate via surface groups which were characterized

Oxygen reduction in acid media: influence of the heat treatment on the FeNPc(1–20 isomer mixture impregnated on carbon blacks and active charcoals

Oxygen reduction with the aid of a number of FeNPc(1–2) impregnated carbon supports in sulphuric acid solutions has been investigated.\ud \ud Loading of the carbon samples amounted to about 10 wt.%. After a 10 day stay in the aerated solutions the samples were investigated with rotating disk electrode and X-ray photoelectron spectroscopy techniques. The most active and stable samples correspond to mono- or submonolayers of FeNPc deposited on high dibutylphthalate adsorption carbon blacks. Comparison with data obtained previously on Norit BrX impregnations emphasizes the rôle of the electron density on the inner nitrogen atoms rather than that on the iron centres

Oxygen reduction in acid media on supported iron naphthalocyanine: Effect of isomer configuration and pyrolysis

O2 reduction in H2SO4 medium has been investigated on FeNPc impregnations on Norit BrX by the rotating disk electrode technique. Important differences in activity and stability were found between the 1,2- and 2,3-FeNPc isomers (pyrolysed or not). XPS analyses show, for the most inactive sample, strong demetallation and nitrogen losses. This phenomenon can be attributed to the differences in flexibility between the FeNPc isomers, which influences their stabilization on the substrate

Oxygen reduction in an acid medium : electrocatalysis by CoNPc(1,2) impregnated on a carbon black support; effect of loading and heat treatment

O2 reduction in an acid medium has been investigated on a transition metal macrocycle, CoNPc(1,2), impregnated on a carbon black support with a high dibutylphthalate adsorption value, using a rotating disk electrode and voltammetry techniques described previously, combined with X-ray photoelectron spectroscopy measurements. Optimal activity was found for a bilayer coverage (n = 2) at 17%-18% w/w loading. Heat treatment seems to be beneficial for n 3: it increases the overall number N of exchanged electrons and improves the electrode wetting. For the most active samples, mixed Co(II)/Co(III) valencies were displayed

Effect of the nature of iron naphthalocyanine supports on their activity for O2 reduction in acid media

Samples of iron naphthalocyanine (FeNPc) have been synthesized on carbon black and on active charcoal (ex-CH4 and Norit BrX). These samples were examined by RDE and voltammetric techniques. After prolonged contact with acids, the samples were also investigated by XPS. The impregnations on Norit proved to be stable in H2SO4 solutions, whereas the ex-CH4 samples were stable only in HC1O4 solution. The XPS data indicated that in catalytically active samples the in situ synthesized FeNPc molecules are deformed. The activity of FeNPc on Norit BrX remains higher than on ex-CH4, despite considerable demetallation

Oxygen reduction in acid media catalysed by heat treated cobalt tetraazaannulene supported on an active charcoal: Correlations between the performances after longevity tests and the active site configuration as seen by XPS and ToF-SIMS

The influence of heat treatment (HT) on CoTAA supported on SX Ultra samples before and after electrochemical tests has been investigated using the rotating disk electrode (RDE) technique and cyclic voltammetry, The heat treated sample configuration was also scrutinized by two different surface spectroscopic techniques: X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). After a 100 h polarization period at 500 mV (RHE) (diffusion activation domain), optimal performances were found to occur with the 600 degrees C heat treated samples (HT 600). However, the most salient feature was the observation of a fair activity and stability for the 800 degrees C heat treated samples (HT 800). Similar behavior was exhibited both with H2SO4 and Nafion(R) electrolytes. Collected data could be interpreted on the basis of RDE and cyclic voltammetry theories, suggesting a fast dioxygen mass transfer within the catalytic material in comparison with interfacial process kinetics. After these electrochemical tests a complete demetallation was taking place, as seen by XPS within the HT 800 samples. A protonation process was also clearly identified on the nitrogen ions. An attempt has been made to propose a catalytic cycle in which variations of the different nitrogen oxidation states are occuring. The major obstacle encountered lay in the lack of XPS evidence of the high nitrogen oxidation states. From ToF-SIMS data the existence of bonding between C, N and O can be established with NO3- formation. Under the same treatment conditions this process occurs differently with H(2)TAA precursor. From the collected data it turned out that catalytic cycles involving nitrogen ions possess a lower turnover than those with cobalt ion participation

O2 electrocatalysis in acid media on iron naphthalocyanine impregnations. Effect of nitric acid treatment on different carbon black supports

O2 electrocatalysis on (2,3)FeNPc impregnations on different carbon blacks was investigated in H2SO4 medium. The effect of nitric acid treatment on the carbon black support is to enhance both the activity and stability of the catalyst. Moreover, as seen by XPS, the dissolution of iron is impeded by this oxidation treatment which, however, does not increase the density of active sites with the BET surface area. From the data presented, a redox mechanism can hardly be invoked, in contrast to the situation for FeNPc impregnations on active charcoals