MnO2 Nanoflowers Deposited on Graphene Paper as Electrode Materials for Supercapacitors

We recently reported a simple and cost-effective green method to produce free-standing, flexible, and highly conductive electrochemically exfoliated graphene paper (GrP) for a supercapacitor application. To improve the capacitance behavior of GrP, manganese dioxide (MnO 2 ) was electrochemically deposited on GrP with different number of MnO 2 cycles. After the electrochemical deposition process, MnO 2 nanoflowers were formed, which provide a fast transfer of electrolyte ions. After 10 cycles of electrodeposition, MnO 2 -coated GrP (GrP/10-MnO 2, which is the optimal composition) exhibited an excellent capacitive performance with a high specific capacitance of 385.2 F·g –1 at 1 mV·s –1 in 0.1 M Na 2 SO 4 electrolyte and outstanding capacitance retention after 5000 consecutive cycles. Taking advantage of both superior mechanical and capacitance behavior of GrP and GrP/10-MnO 2 electrodes, a flexible solid-state asymmetric supercapacitor (SASc) device was assembled using GrP/10-MnO 2 and GrP as positive and negative electrode, respectively. The fabricated SASc device exhibited not only high areal capacitances of 76.8 mF cm –2 at a current density of 0.05 mA cm –2 but also excellent cycling stability of 82.2% after 5000 consecutive galvanostatic charge/discharge cycles. This flexible supercapacitor can also deliver a high energy density of 6.14 mWh·cm –2 with a power density of 36 mW·cm –2 . This research represents a new direction for exploring the potential of free-standing GrP and its nanocomposites in flexible energy-storage systems.