The main challenge for the development of a high efficiency supercapacitor is the electrode material. Developing electrode materials with high specific electrical capacitance and low electrical resistance enables an increase in the energy accumulated in the device. In addition, it is expected that the electrode material presents a simple procedure for preparation having low production cost and being environmentally friendly. This work is based on the deposition of silver nanoparticles on activated carbon felt (Ag@ACF) as a supercapacitor electrode. The samples were characterized by field emission gun scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and textural analysis. Supercapacitor behavior was evaluated by galvanostatic charge-discharge curves, cyclic voltammetry and electrochemical impedance spectroscopy using a symmetrical two-electrode Swagelok type cell, and three different aqueous solution electrolytes: 2 M H 2 SO 4 , 6 M KOH and 1 M Na 2 SO 4. Ag@ACF presented a high specific capacitance in KOH, about 170 F g-1 , which makes it an interesting material for supercapacitor electrodes and it showed good specific electrical capacitance, low resistance and high cyclability.

In this study, activated biochar was produced using pilot-scale technologies of fast pyrolysis and activation to create desirable morphology, surface chemistry, and adsorptive properties for application in supercapacitors. First, residues from white birch were converted into biochar by fast pyrolysis (~ 450 °C). Then, physical (using CO2) or chemical (using KOH) activation was carried out in a homemade pilot-scale furnace at 900 °C. These synthesized materials presented distinct porosity structures: micro-/mesoporous (CO2 material) and highly microporous (KOH material), reaching surface areas of up to 1700 m 2 g-1. Electrochemical results showed that KOH-activated biochar had higher specific electrical capacitance in both acidic and neutral electrolytes with a maximum specific capacitance value of 350 and 118 F g-1 at 1 A g-1 , respectively; while, for CO2activated biochar, the maximum obtained values were 204 and 14 F g-1. The greater proportion of oxygenated and nitrogenated functional groups on the surface of the KOH activated biochar, along with its high surface area (with wider porosity), improved its performance as a supercapacitor electrode. Specifically, the low proportion of ultramicropores was determinant for its better electrochemical behavior, especially in the neutral electrolyte. Indeed, these results are similar to those found in the literature on the electrical capacitance of carbonaceous materials synthesized in a small-scale furnace. Thus, the chemical-activated biochar made from wood residues in pilot-scale furnaces is a promising material for use as electrodes for supercapacitors.

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