Free-standing, layered graphene monoliths for long-life supercapacitor

Fabricating free-standing film/paper or 3D material without additive binder is of great importance to maintain its original architectures and properties. Here, we for the first time introduce a simple, facile approach to fabricate a free-standing, layered N-doping reduced graphene oxide (NRGO) monolith for supercapacitor, firstly mixing graphene oxide (GO) with urea, and lastly taking a short-term flame bath. It is found that urea is a key sacrificial grasper, which can effectively prevent reduced GO (RGO) sheets from being peeled off in flame bath. Moreover, 3.5-7.0 at.% of N elements are successfully introduced into RGO skeleton. These structural characteristics are translated into high specific capacitance (323.7 F g(-1) at 1 A g(-1), higher than RGO powder (252.1 F g(-1))), ultra-high coulombic efficiency (125% at 1 A g(-1)) and superior cycle performance with a 9.2% improvement in specific capacitance after 50,000 cycles at 30 A g(-1). Relatively, only 69.3% of the specific capacitance for RGO powder remains after 10,000 cycles at 30 A g(-1). Compared with RGO powder, NRGO shows obviously improvement in coulombic efficiency, energy efficiency, and especially in cycle stability. Thus, this layered NRGO not only shows a high energy storage capacity, but also successfully solves the stability problem in the long-term charge/discharge cycle. This provides a novel clue for designing long-life graphene-based electrode materials for supercapacitor.