Hierarchical porous fluorine-doped silicon oxycarbide derived materials: Physicochemical characterization and electrochemical behaviour

Novel hierarchical micro-meso-macroporous fluorine-doped silicon oxycarbide derived materials have been obtained by HF etching of silicon oxycarbides pyrolyzed at different temperatures. The influence of etching time (1 or 24 h) and pyrolysis temperature (from 1100 to 1400 °C) on the selective removal of the silica nano-domains present in the silicon oxycarbide and the appearance of oxygen and fluorine functionalities have been determined and evaluated in terms of their electrochemical response. The insertion of fluorine in the silicon oxycarbide matrix (Si–O(F) bonds) and free carbon phase (C–F semi-ionic and C–F covalent bonds) was corroborated. The materials pyrolyzed at 1300–1400 °C and etched during 24 h show values of specific capacitance as high as 225-165 Fg-1 (0.1–30 Ag-1) using a symmetrical configuration and H2SO4 1 M as electrolyte. These materials displayed energy density values of 28-19 Whkg−1 (0.1–45 kWkg-1). The hierarchical microstructure in conjunction with the oxygen and fluorine functionalities are essential in order to explain their good electrochemical response. In particular, those materials present the highest amount of meso (3–10 nm) and larger meso-macropores and the highest content of fluorine in their composition. Then, fluorine-doped silicon oxycarbide derived materials can be potentially used as electrodes for supercapacitors in the field of energy storage applications.