Sulfur-rich carbon cryogels for supercapacitors with improved conductivity and wettability

Sulfur-rich carbon cryogels derived from 2-thiophenecarboxaldehyde and resorcinol were synthesized through sol–gel processing, which demonstrated good stability with less than 4% capacitance loss after 1000 charge–discharge cycles. Pyrolysis of sulfur-rich carbon at higher temperatures resulted in decreased electrical conductivity, which was caused by the degree of graphitization deteriorating at high temperatures. An increased amount of sulfur can effectively improve the wetting behavior of the carbon electrode in organic electrolytes. Specifically, when the sulfur content is 2.5 at%, the electrode was completely wetted. Additionally, pseudocapacitive reactions introduced from sulfur were observed in this electrolyte. Synergistic effects of sulfur and pore structure controlled the final electrochemical properties. The sulfur-containing sample pyrolyzed at 1000 °C had the best specific capacitance and impedance performance. When activated in air without sol–gel processing optimization, the sulfur-modified carbon demonstrated a capacitance of 94.4 F g−1 in organic electrolytes.