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Catalysis Science & Technology


Bifunctionality of the pyrone functional group in oxidized carbon nanotubes towards Oxygen Reduction Reaction


Authors: Inês Rocha; Salomé Soares; Jose Luis Figueiredo; Cristina Freire; Manuel Fernando Pereira

Publication Date: -0001-11-30  Article ASAP

Oxidised carbon nanotubes were submitted to a controlled thermal treatment at different temperatures, under N2-atmosphere. X-ray photoelectron spectroscopy confirmed the presence of acid and basic groups on the starting sample. For samples submitted to higher temperatures, only the basic oxygen functional groups remained on the surface, namely quinone and pyrone groups. The oxygen reduction reaction (ORR) performance of all electrocatalysts was evaluated under alkaline medium in O2-saturated solutions. Increasing the basic character leads to a better ORR activity in terms of potential onset values (from -0.230 to -0.194 V). Two well-defined cathodic peaks associated to the reduction of oxygen are observed on the cyclic voltammograms when the acid oxygen groups are removed from the electrocatalyst surface. The computational simulations of a carbon surface functionalized with quinone and pyrone groups were a relevant tool to explain the presence of the two cathodic peaks. The quinone sites only favour the physisorption of oxygen, while oxygen adsorption on the pyrone group may occur by both physisorption and chemisorption processes, involving a high electron densities. Consequently, pyrone may require less energy to initiate the ORR mechanism, presenting a less negative cathodic peak potential value, compared with the peak of the quinone group.  Read more