Microwave-Assisted Hydrothermal Preparation of Corn Straw Hydrochar as Supercapacitor Electrode Materials

Abstract

In this work, we propose the microwave-assisted hydrothermal activation method to synthesize supercapacitor electrode materials from corn straw under a small amount of the potassium catalyst (30 wt %), which can meet the environmental protection and low-cost requirement. With the extension of radiation time from 40 to 100 min, the pore structure of hydrochar expands from the micropore to hierarchical pore, and the microstructure evolves from an amorphous structure to graphene-like sheets. Microwave-assisted hydrothermal activation can control the synergistic development of hierarchical pore and graphene-like sheets of hydrochar under the condition of using a lesser amount of the catalyst. The as-obtained HTC-40/70/100 shows an excellent graphitization degree and the developed hierarchical pores. By comparing the electrochemical performance of the symmetrical capacitor devices composed of corn straw hydrochar and pyrochar in organic electrolytes, we have found that the hydrochar is suitable for organic system symmetric capacitance, and the pore structure and graphitization degree are closely related to the transmission of ions and electrons in the electrolyte. Therefore, HTC-100 with a high specific surface area (1781 m 2 /g) and highly ordered microstructure has the best electrochemical performance.

Synthetic Methodologies and Energy Storage/Conversion Applications of Porous Carbon Nanosheets: A Systematic Review

“…Liu et al utilized the microwave-assisted hydrothermal method to fabricate PCNS from corn straw using 30 wt % KOH microwave irradiated at 1000 W and 2450 MHz for different time intervals (40, 70, and 100 min) where the extended irradiation leads to hierarchical pores. The obtained 2D PCNS possessed excellent graphitization degrees and high SSAs of up to 1781 m 2 g –1 . Chen et al synthesized ultrathin graphene sheets (2–10 atomic layers) with interlayer spacings of 0.3362 nm through hydrothermal and graphitization processes utilizing wheat straw as a precursor .…”

“…On the basis of the pore diameter, they can be classified into microporous (pore size < 2 nm), mesoporous (2 nm < pore size < 50 nm), and/or macroporous (pore size > 50 nm) carbons . Their applicability in the above-mentioned fields is not only due to their superior chemical and physical properties like high thermal and electrical conductivity, good chemical stability, and low density but also due to the ease of availability. , However, the porous carbons, which are prepared by the carbonization of polymer or biomass precursors and the following activation always have complicated and uncontrollable porous structure, resulting in low surface utilization and very large mass transfer resistance.…”

Recent advancement of biomass-derived porous carbon based materials for energy and environmental remediation applications

“…The authors have suggested that the microwave irradiation not only increases the rate of the hydrolysis reaction, which is signicant for the depolymerization and rearrangement of the precursor carbon skeleton, but also offers a graphitization effect by facilitating the motion of the catalyst (potassium; 30 wt%) in between the carbon layers. 161 Likewise, P, N-rich agricultural (rapeseed) and antibiotic (lincomycin) residual feedstocks were used for the preparation of hydrochars via microwave-assisted HTC method for environmental applications. 162 The advantages of HTC process over pyrolysis include improved energy consumption, minimized toxic wastes generation, higher yield ($30-60 wt%), retention of surface hydroxyl and carboxylic functional groups and doping of heteroatoms.…”

Innovative and Economically Beneficial Use of Corn and Corn Products in Electrochemical Energy Storage Applications

“…Liu et al proposed a microwave-aided hydrothermal activation method to fabricate supercapacitor electrode materials using corn stover with the presence of potassiumbased catalyst. 22 Dried corn stover and potassium hydroxide powders in a weight ratio of 2:1 are put in a hydrothermal tank and mixed with deionized water, as shown in Figure 5a. The reaction tank is put into a microwave reactor, heated at 1000 W and 2450 MHz, and held for 40, 70, and 100 min, respectively.…”

“…(e–g) TEM images of the hydrochar sample made with radiation times of 40, 70, and 100 min, respectively. Adapted with permission from ref . Copyright 2020 American Chemical Society.…”