Nitrogen and oxygen co-doped carbon micro-foams derived from gelatin as high-performance cathode materials of Zn-ion capacitors

Nitrogen and oxygen co-doped micro-foam like mesoporous carbons are prepared from gelatin, an abundant hydrolyzed product of animal collagen with high carbon content and fruitful heteroatoms. Benefiting from the swelled structure of gelatin after pre‑carbonization at 300 °C, the following moderate chemical activation with KOH results in highly mesoporous carbons with specific surface area over 3000 m2 g−1 and total pore volume larger than 1.96 cm3 g−1 while preserving the micro-foam structure. As cathode materials of zinc ion capacitors (ZICs), the carbon micro-foams display very encouraging energy storage performance in both organic and aqueous electrolytes. A high energy density of 90 Wh kg−1 is obtained at a power density of 445 W kg−1 in 1 M Zn(CF3SO3)2/DMF (N, N-dimethylformamide) electrolyte, whereas in 1 M ZnSO4 aqueous electrolyte the ZIC exhibits much better rate capability (54 Wh kg−1 at 14650 W kg−1) possibly due to the better wettability and higher ionic conductivity. These excellent electrochemical properties suggest that the N and O co-doped mesoporous carbon micro-foams derived from gelatin can be potential cathode materials of high-performance Zn-ion capacitors.