Insights on the Electrochemical Oxidation of Ordered Mesoporous Carbons

Ordered mesoporous carbon materials (OMC) present a developed porosity, making them promising candidates for electrochemical energy-conversion devices. However, OMC undergo electrochemical oxidation causing the degradation of electrodes and exhibit low electrical conductivities due to their amorphous carbon structure. To address these issues, OMC can be graphitized by thermal treatments. Herein, the electrooxidation behavior of different OMC, prior and upon graphitization, is studied by chronoamperometry in a highly acidic electrolyte (0.5 M H2SO4). Several oxidation potentials and temperatures are used to gain insights on the electrooxidation mechanism. Potential holding tests evidenced differences in the oxidation behavior of as-synthesized and graphitized materials. Graphitization results in a strong decrease of the oxidation charge from 93 to 7% depending on the carbon properties, applied potential and temperature. Temperature plays an important role on carbon degradation of not-graphitized OMC, with a strong electrochemical capacitance loss (90%–93%) after tests at 40 °C and 60 °C. Conversely, graphitized materials present a raise of the capacitance by the creation of oxygen-functionalities as confirmed by post-mortem X-ray photoelectron spectra analysis. Additionally, graphitized materials show an increase of the apparent activation energy associated to electrooxidation (7 times higher), indicative of their improved resistance.