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 (MnO2) was electrochemically deposited on GrP with different number of MnO2 cycles. After the electrochemical deposition process, MnO2 nanoflowers were formed, which provide a fast transfer of electrolyte ions. After 10 cycles of electrodeposition, MnO2-coated GrP (GrP/10-MnO2, 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 Na2SO4 electrolyte and outstanding capacitance retention after 5000 consecutive cycles. Taking advantage of both superior mechanical and capacitance behavior of GrP and GrP/10-MnO2 electrodes, a flexible solid-state asymmetric supercapacitor (SASc) device was assembled using GrP/10-MnO2 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.