Effect of visible light and electrode wetting on the capacitive performance of S- and N-doped nanoporous carbons: Importance of surface chemistry

Nanoporous carbons with graphitic domains were synthesized from a polymer containing sulfur and nitrogen. The materials were characterized using adsorption of nitrogen, potentiometric titration TA/MS, XPS, TEM and XRD. Then they were tested as supercapacitors in three-electrode cell and under visible light irradiation after extensive wetting either in water or a sulfuric acid electrolyte. The capacitance up to 450 F/g was measured in spite of a relatively low surface (<850 m²/g). The surface chemistry, and especially sulfur and nitrogen containing functional groups, were found of paramount importance for the capacitive behavior and for the effective pore space utilization by the electrolyte ions. Photocurrent measured in light also affects the capacitance. Its generation is linked to the excitation of sulfonic/sulfoxide chromophores-like moieties decorating the surface of the polymer-derived carbons.