Corn stover‐derived porous carbon for asymmetric supercapacitors

Abstract

In this investigation, hydrothermal liquefaction‐derived hydrochar from pulverized corn stover (avg. particle size 1.12 mm and ash content 6.75 wt%) is chemically activated with aqueous KOH in the presence of Pluronic F127 surfactant and thermally treated further up to 800°C to generate porous carbon (POC) with higher specific surface area and porosity. POC obtained under different processing conditions is thoroughly characterized by Brunauer‐Emmett‐Teller surface area analyzer, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Metallic impurity present in POC is characterized by inductively coupled plasma mass spectrometry. Higher specific surface area POC is observed with the use of the surfactant during the activation process. Fully characterized POC is used with (Mn, Ti)‐mixed oxide electrode to fabricate asymmetric supercapacitor (ASC). Specific capacitance of ASC is measured by cyclic voltammetry (CV) technique using Gamry G‐300 potentiostat/galvanostat/ZRA. CV plots are obtained with different voltage scan rates whereas galvanostatic charge‐discharge plots are studied by varying the current density. Renewable corn stover‐derived POC prepared using Pluronic F127/KOH activation method is found to be highly suitable as an electrode material because of higher capacitance and electrochemical stability over 100 charging‐discharging cycles.

Hybrid Mesoporous Carbon/Copper Ferrite Electrode for Asymmetric Supercapacitors

“…The average pore size of POC@Cu-ferrite was observed as 4.5 nm. It is to be noted that the average pore size for POC was 3.8 nm, which was reported elsewhere [ 40 ]. The mesoporous structure of POC@Cu-ferrite can facilitate the redox reactions in ASC and improve the ion diffusivity across the electrode/electrolyte interface [ 45 ].…”

“…Specific surface area (SSA) of the Cu-ferrite and POC@Cu-ferrite from the BET isotherms was determined as 4.7 m 2 /g and 1068 m 2 /g, respectively. SSA of the POC material alone was 1607 m 2 /g; additional details can be found elsewhere [ 40 ]. The pore volume was determined as 0.00068 cm 3 /g, 0.86 cm 3 /g, and 0.72 cm 3 /g for the Cu-ferrite, POC, and POC@Cu-ferrite materials, respectively.…”

“…The stability analysis further shows a capacitance retention of 89% and 64% at 0.02 A/g over 100 cycles for ASC-2 and ASC-3, respectively, which indicates a superior cyclic stability for the POC@Cu-ferrite-based ASC. Due to the monolithic nature of the electrode, packaging of ASC, and the drying issue associated with aqueous electrolyte, stability study beyond 100 cycles was not feasible [ 40 ]. At higher current densities, Faradaic reactions between the ASC electrode and electrolyte become sluggish, causing a reduction in specific capacitance [ 58 ].…”

“…Finally, it was dried at 60 °C in a conventional oven. Additional details about POC preparation can be found elsewhere [ 28 , 30 , 31 , 32 , 36 , 37 , 38 , 39 , 40 ].…”

“…The working electrode along with a Ag/AgCl reference electrode and a Pt wire counter electrode were used in a typical 3-cell setup to determine the electrochemical performance. Additional details can be found elsewhere [ 31 , 40 ].…”