N-doped carbon materials were obtained using polyaniline (PANI) as precursor. Heat treatment of PANI and de-doped PANI (PANId) was performed using different temperatures-600 and 800 ºC-. Two different atmospheres were used during the treatment: an inert atmosphere (N 2) and another one consisting on a slightly oxidizing mixture of gases (3000 ppm O 2 in N 2). The prepared materials at 800 ºC showed high values of capacitance, up to 170 and 255 F g-1 in basic and acid electrolytes, respectively, in spite of their low surface area. The electrocatalytic activity towards oxygen reduction reaction (ORR) of all materials was studied in basic and acid media. The heat treated materials at 600 ºC did not show a good electrocatalytic activity due to their poor electrical conductivity. On the other hand, heat-treated materials at 800 ºC showed an enhanced catalytic activity due to their higher conductivity and the presence of nitrogen and oxygen functionalities in the carbon surface. Interestingly, the heat treatment at 800 ºC using a slightly oxidant atmosphere produces carbon materials with much higher ORR activity which seems to be related to the larger amount of N-edge and O-edge sites. Preliminary computational studies suggest that the presence of these nitrogen and oxygen functionalities in the vicinities of the carbon atom improves the catalytic performance of N-doped carbon materials in the ORR and that two adjacent active sites can produce the O 2 reduction to H 2 O through a 4 electrons pathway.

The role of porosity, and more specifically, microporosity, in the performance of carbon materials as Oxygen Reduction Reaction (ORR) catalysts in alkaline medium still has to be clarified. For this purpose, a highly microporous KOH-activated carbon and a microporous char have been prepared and their ORR performance in alkaline media were compared to that of two commercial carbon blacks with low and high surface areas, respectively. Interestingly, all carbon materials show a two-wave electrocatalytic process, where the limiting current and the number of electron transferred increase when going to more negative potentials. The limiting current and onset potential of the second wave is positively related to the amount of microporosity, and H 2 O 2 electrochemical reduction tests have confirmed that the second wave could be related to the catalytic activity towards this reaction. In accordance to these findings, a model is developed that takes into account narrow and wide micropores in both charge transfer reactions and the mass transfer rate of O 2 and H 2 O 2. This model successfully reproduces the experimental electrochemical response during ORR of the analyzed porous carbon materials and suggests the important role of narrow micropores in H 2 O 2 reduction.

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Glucose oxidase has been immobilized on multiwall and herringbone carbon nanotubes for glucose biosensing.

A new portable electrochemical sensor based on 4-aminobenzoic acid-modified herringbone carbon nanotubes (hCNTs-4ABA/Au-IDA) has been developed for the simultaneous determination of ascorbic acid (AA) and uric acid (UA) in physiological fluids. AA and UA were quantified by chronoamperometry at 0.1 and 0.32 V, respectively, in phosphate buffer solution (PBS 0.25 M, pH 7.0). Significant results were obtained for the separate quantification of AA and UA, with a limit of detection (LOD) of 0.65 μM for both analytes, and sensitivities of (9.0 ± 0.4) A g mM and (8.8 ± 0.3) A g mM for AA and UA, respectively. Repeatability was studied at 50 μM for AA and UA, providing relative standard deviations (RSD) lower than 9%. Additions of glucose, dopamine and epinephrine did not interfere with the AA and UA determination. Furthermore, UA did not interfere with AA determination at 0.1 V, although AA additions increased the current recorded at 0.32 V. The method has been successfully applied to human urine, perspiration and serum samples, without significant matrix effects, which allows for the use of an external calibration and the analysis of all the matrices investigated.