N-rich reduced graphene oxide film with cross-coupled porous networks as free-standing electrode for high performance supercapacitors

Abstract Graphene films suffer from poor electrochemical performance due to the undesirable ion diffusion inside its deep area and only electrical double layer absorption mechanism. Here, we proposed a freeze casting method for fabricating the N-rich holey reduced graphene oxide films (Freeze-dried N-HRGO) bearing cross-coupled porous ion diffusion networks. The H2O2 etching and modified vacuum filtration process generate abundant pore structures inside films, which act as ion diffusion path for promoting electrochemical performance. In addition, the N sites serve as pseudocapacitance contributor to react with electrolyte ions, which greatly enhance the specific capacitance. As a result, the freeze-dried N-HRGO films show a high specific capacitance of 528 F g−1 at a current density of 1 A g−1. When assembled into symmetrical supercapacitor, it delivers a high energy density of 14.0 Wh kg−1 and excellent cycle life (89.3% capacity retention after 5000 cycles at 2 A g−1).