3D porous binary-heteroatom doped carbon nanosheet/electrochemically exfoliated graphene hybrids for high performance flexible solid-state supercapacitors

Abstract

Graphene is a promising electrode material for high-performance supercapacitors. However, its intrinsic large surface area is usually underutilized as a result of the unexpected re-stacking upon cycling. Here a novel N,S-codoped carbon nanosheet/electrochemically exfoliated graphene hybrid (denoted as CNS/EG) is prepared through a feasible electrochemical exfoliation process followed by a sol–gel method, and effective activation is further conducted to fabricate the activated CNS/EG (a-CNS/EG). The as-prepared a-CNS/EG with heteroatom doping characteristics and high accessible surface area (1532 m² g⁻¹) is used as an electrode material for supercapacitors, exhibiting remarkable specific capacitances of 341 and 200 F g⁻¹ at current densities of 0.1 and 10 A g⁻¹ in 6 mol L⁻¹ KOH electrolyte, respectively. Furthermore, the symmetric flexible solid-state supercapacitors assembled with the a-CNS/EG electrode and PVA/KOH gel electrolyte display a remarkable capacitance retention of 99% after 10 000 cycles at 3 A g⁻¹. The fascinating electrochemical performance is due to the distinctive structure of tiny carbon nanosheets uniformly distributed in electrochemically exfoliated graphene with N,S-codoping, which can effectively prevent the re-stacking and bring about the faradaic contribution. What's more, the large ion storage and rapid ion transfer resulting from the high surface area and hierarchical pore structure also play an important role in enhancing the electrical double layer capacitance.