A sustainable approach to produce activated carbons from pecan nutshell waste for environmentally friendly supercapacitors

Activated carbons are key electrode materials for supercapacitors (SCs) widely used in commercial devices. Here we investigate the preparation of activated solar carbons (ASCs) from pecan nutshell waste for their use as electrode materials for SCs. The ASCs are prepared using a sustainable process where concentrated solar energy is used as heat source for the one-step carbonization/chemical activation using H3PO4. From physical characterization we observed that our prepared ASCs are amorphous carbons, which have well-developed microporous surface of different features related with a pretreatment of pecan nutshell. The ASCs are electrochemically evaluated by cyclic voltammetry in four aqueous electrolytes using a three-electrode system, obtaining capacitances at 5 mVs(-1) of 150 and 129 Fg(-1) in acidic (0.5 M H2SO4) and environmentally-friendly neutral (1 M CH3COONa) electrolytes, respectively. Finally, we assembled asymmetric carbon-carbon SC cells showing excellent performance compared to a commercial activated carbon, with capacitances around 30 Fg(-1) at 0.5 A g(-1) with only -10% of capacitance loss after 5000 cycles, reveling a high stability, and a widest voltage window with the 1 M CH3COONa electrolyte. Our study provides a novel sustainable approach to use agricultural waste biomass to produce useful electrode materials for energy storage devices using concentrated solar energy. (C) 2019 Elsevier Ltd. All rights reserved.