High mass loading MnO2/graphite felt electrode with marked stability over a wide potential window of 1.9 V for supercapacitor application

Herein, a facile method is employed to prepare a high mass loading (3.7 mg cm−2) MnO2/graphite felt (GF) to serve as a pseudocapacitive electrode type with a marked extended potential window of 1.9 V. MnO2 is electrochemically deposited on 3-D porous GF substrate via optimizing the bath concentration and deposition potential window. GF is in-situ modified concurrently with the electrodeposition of MnO2. Starting from a high positive potential, GF is modified via functionalization and making defects in its fibers. Moving toward lower potential, the amount of electrodeposited MnO2 is increased. Extending the potential window via moving toward more negative values, the loading amount of MnO2 is increased. Also, increasing the permanganate ions concentration, the degree of GF modification, and the loaded amount of MnO2 active material are increased. In-situ modification of GF is examined by SEM, EDX, XPS, Raman, and contact angle measurements. Interestingly, MnO2 forms a strong adhere uniform coat on the surface of the in situ modified GF resulting in high specific capacitance and extraordinary stability. Surprisingly, MnO2/GF displays a high specific capacitance of 832 mF cm−2 (226 F g−1) at a low current density of 1.4 mA cm−2 over a large potential window. Even though MnO2/GF operates in a large potential window, the specific capacitance was retained at 118 % at a current density of 14 mA cm−2 for 9000 cycles with excellent efficiency up to 98%. The excellent capacitive performance of MnO2/GF is attributed to the 3-D porous structure of GF with enhanced hydrophilicity, electronic conductivity, and strong adhering of MnO2 together with enhanced electrolyte accessibility to the underneath layers of MnO2 during cycling of the electrode over 9000 cycles.