Fabrication of Multi‐Layered Paper‐Based Supercapacitor Anode by Growing Cu(OH)2 Nanorods on Oxygen Functional Groups‐Rich Sponge‐Like Carbon Fibers

Abstract This work addresses the challenges in developing carbon fiber paper‐based supercapacitors (SCs) with high energy density by focusing on the limited capacity of carbon fiber. To overcome this limitation, a sponge‐like porous carbon fiber paper enriched with oxygen functional groups (OFGs) is prepared, and Cu(OH) 2 nanorods are grown on its surface to construct the SC anode. This design results in a multi‐layered carbon fiber paper‐based electrode with a specific structure and enhanced capacitance. The Cu(OH) 2 @PCFP anode exhibits an areal capacitance of 547.83 mF cm −2 at a current density of 1 mA cm −2 and demonstrates excellent capacitance retention of 99.8% after 10 000 cycles. Theoretical calculations further confirm that the Cu(OH) 2 /OFGs‐graphite heterostructure exhibits higher conductivity, facilitating faster charge transfer. A solid‐state SC is successfully assembled using Ketjen Black@PCFP as the cathode and KOH/PVA as the gel electrolyte. The resulting device exhibits an energy density of 0.21 Wh cm −2 at 1.50 mW cm −2 , surpassing the performance of reported Cu(OH) 2 SCs. This approach, combining materials design with an understanding of underlying mechanisms, not only expands the range of electrode materials but also provides valuable insights for the development of high‐capacity energy storage devices.