Using thiourea as a catalytic redox-active additive to enhance the performance of pseudocapacitive supercapacitors

Adding redox-active additives into the electrolyte is an effective way to enhance the performance of pseudocapacitive supercapacitors (SCs). However, the applications of these redox-active additives are limited by their high molecular weight and narrow redox potential window. Herein, we report thiourea (TU) as a catalytic redox-active additive to enhance the performance of a supercapacitor based on copper nanocrystal@nitrogen-doped carbon composites (Cu@N-C), whose capacitance was increased 5.9 fold: from 194 mF cm−2 (15.7 mA h g−1, without TU) to 1154 mF cm−2 (93.3 mA h g−1, with TU). The optimized Cu@N-C-600 electrode presents a wide voltage window (1.8 V) and an extremely high capacitance (9571 mF cm−2, 775.4 mA h g−1 at 5 mA cm−2), which is mainly attributed to the pseudocapacitance from the reversible redox reaction of TU and Cu compounds. The porous nitrogen-doped carbon matrix immobilizes and protects the highly active Cu nanocrystals, and also facilitates charge and mass transfer between the electrode and electrolyte. For the symmetrical SC based on Cu@N-C-600, the energy density and power density reach 314 μW h cm−2 and 2798 μW cm−2, respectively, superior to those of most of the inorganic material-based SCs. This work demonstrates that TU is an efficient redox-active additive to improve the performance of pseudocapacitive SCs.