Balancing the electrical double layer capacitance and pseudocapacitance of hetero-atom doped carbon.

Heteroatom-doped carbonaceous materials derived from polymers are emerging as a new class of promising supercapacitor electrodes. These electrodes have both electrical double layer capacitance (from carbon matrices) and pseudo-capacitance (from hetero-atoms). Balancing the electrical double layer capacitance and pseudo-capacitance is a key to achieve large capacitance at ultrafast current densities. Here we investigate the influence of pyrolysis temperature on capacitive performance of hetero-atom (oxygen and nitrogen) doped carbons derived from polypyrrole nanowire arrays. Structural and electrochemical characterization reveal that the concentration of hetero-atoms as well as the ratio of electrical double layer capacitance and pseudo-capacitance can be tuned by varying the pyrolysis temperature. In fact the hetero-atom doped carbon sample obtained at a relatively lower pyrolysis temperature (500 °C) exhibits the optimal capacitive performance. It yields an outstanding areal capacitance of 324 mF cm-2 at 1 mA cm-2 (141 F g-1@0.43 A g-1), and more importantly, retains an areal capacitance of 184.7 mF cm-2 (80.3 F g-1@43.5 A g-1) at an ultrahigh current density of 100 mA cm-2. An asymmetric supercapacitor consisting of hetero-atom doped carbon as an anode delivers a maximum volumetric energy density of 1.7 mW h cm-3 at a volumetric power density of 0.014 W cm-3, which is among the best values reported for asymmetric supercapacitors.