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

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)).

Automated summary

The freeze-dried N-HRGO films fabricated by a freeze casting method exhibit excellent electrochemical performance due to their cross-coupled porous ion diffusion networks, abundant pore structures for promoting ion diffusion, and nitrogen sites enhancing specific capacitance, resulting in a high specific capacitance of 528 F g(-1) and a high energy density of 14.0 Wh kg(-1) with excellent cycle life (89.3% capacity retention after 5000 cycles at 2 A g(-1)) when assembled into a symmetrical supercapacitor.