Superior capacitive and electrocatalytic properties of carbonized nanostructured polyaniline upon a low-temperature hydrothermal treatment

Carbonized nanostructured polyaniline (C.PANI) was hydrothermally treated in 1 mol dm−3 KOH at 200 °C. The treatment caused significant reduction of micropore volume but negligible changes in mesoporous domain, as evidenced by nitrogen adsorption measurements, as well as significant increase of surface N/C and O/C ratios, as evidenced by XPS method. In comparison to the C.PANI precursor, the new material, denoted as C.PANI.HAT200, delivered twice as high gravimetric capacitances, amounting to 363, 220 and 432 F g−1, in 6 mol dm−3 KOH, 2 mol dm−3 KNO3 and 1 mol dm−3 H2SO4, respectively, when measured potentiodynamically at a scan rate of 5 mV s−1. Moreover, its exceptionally high electrocatalytic activity towards the oxygen reduction reaction (ORR), almost one order of magnitude higher than that of C.PANI was evidenced in alkaline media, approaching closely a four-electron pathway. The onset potential for ORR matched the one of platinum-based electrocatalyst. Significant improvements of both capacitive and electrocatalytic properties of C.PANI.HAT200 were discussed in correlation to the modification of surface functional groups. These findings affirm the low temperature hydrothermal post-synthetic modification of N-doped nanocarbons as a route of production of advanced multifunctional carbon materials with exceptional characteristics.