Graphene nano-walls (GNWs) are promising materials that can be used as an electrode in\nelectrochemical devices. We have grown GNWs by inductively-coupled plasma-enhanced chemical\nvapor deposition on stainless steel (AISI304) substrate. In order to enhance the super-capacitive\nproperties of the electrodes, we have deposited a thin layer of MnO2 by electrodeposition method.\nWe studied the effect of annealing temperature on the electrochemical properties of the samples\nbetween 70 Degree C and 600 Degree C. Best performance for supercapacitor applications was obtained after\nannealing at 70 Degree C with a specific capacitance of 104 F g^-1 at 150 mV s^-1 and a cycling stability of\nmore than 14k cycles with excellent coulombic efficiency and 73% capacitance retention.\nElectrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge/discharge\nmeasurements reveal fast proton diffusion (1.3 * 10^-13 cm2â?¢s^-1) and surface redox reaction after\nannealing at 70 Degree C.
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