Cu-modified biomass-derived activated carbons for high performance supercapacitors

Porous carbons are widely used in supercapacitors, owing to their long cycle life and natural abundance. However, most of these electrode materials give a low capacitance, which leads to low energy density. Cu-doped biomass-derived activated carbons (Cu-ACs) were synthesized using a simple, low-cost carbonization and KOH activation method. The copper nanoparticles had mixed valence states (CuO, Cu2O, Cu0) and were uniformly dispersed on the surface of the AC. Due to the fast electron/ion transfer paths provided by the pore structure, and an accelerated redox reaction between the three Cu species, the Cu-ACs achieved an excellent capacitive performance. In a three-electrode system, the Cu-AC sample prepared by KOH activation with a KOH/(Cu+char)mass ratio of 2 had a high specific capacitance of 360 F g−1 at 0.5 A g−1, 1.21 times that of AC (163 F g−1). When it was fabricated into a symmetric capacitor, the device had a good electrochemical performance with a specific capacitance of 143.44 F g−1 at 0.5 A g−1 and a good cyclic stability with an 81.8% capacitance retention after 6000 cycles.