Graphitized Biocarbon Derived from Hydrothermally Liquefied Low-Ash Corn Stover

Abstract

Graphitized biocarbon can be utilized for energy-storage applications such as supercapacitors. The scientific community has geared its attention to obtain such value-added products from abundantly available and low-cost biomass feedstock agricultural residues such as corn stover. Lignocellulosic components embedded within the cell wall of biomass substrates can provide a fine template for enhanced ion storage, transport, and rate capabilities, desirable for electrochemical storage. Presented is the utilization of homogenized low-ash content corn stover milled and sieved to desired specifications, which underwent hydrothermal liquefaction in the presence of Ni-based catalytic salts at 275 °C. The hydrochar obtained using the solid residue extracted from the reaction slurry was washed to acid neutral. The materials were subjected to catalytic activation using ZnCl 2 followed by thermal annealing at 400 °C for morphological and pore size enhancement of the resulting biochar. Carbonization was performed on acid-neutralized hydrochar at 850 °C to further enhance pore structures and increase graphitization for improved conductivity. Catalytic materials exhibited a specific capacitance of 316 F g −1 and held a 100% retention beyond 10,000 cycles. The Brunauer−Emmett−Teller method, Raman spectroscopy, X-ray diffraction, cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy are discussed herein.

Corn stover‐derived porous carbon for asymmetric supercapacitors

“…The ESR values for CS‐POC‐8, CS‐POC‐9, and CS‐POC‐10 were observed as 2.3, 1.7, and 1.8 Ω, respectively. The lowest resistance in CS‐POC‐9 can be attributed to its highest surface area and hierarchical POC material, which improve the electron mobility within the material structure 53,79,80 …”

“…As a comparison, Yu et al 81 reported a specific capacitance of 384 F/g with energy density of 46 Wh/kg and power density of 1 kW/kg for the ASCs fabricated with carbon (derived from typha orientalis leaves) and carbon/MnO 2 electrode. Using various renewable feedstocks, other investigators prepared carbon materials and utilized for the supercapacitors, and their performance evaluations can be found in the literature 49‐53 …”

Sustainable hydrothermal carbon for advanced electrochemical energy storage

“…Similarly, Gupta's group developed a two-step route through the HTL of low-ash corn stover in the presence of Ni-based catalytic salts integrated with ZnCl 2 post-activation to synthesize graphitized biocarbon as an electrode material for SCs, satisfying the cleavage of remaining functional groups and improvement of graphitization. 291 The activated hydrochar presented a surface area of 753 m 2 g −1 and a pore volume of 0.27 cm 3 g −1 and its high graphitization showed a decent electrical conductivity. It was consistently stable during the more than 1000 cycles and exhibited a high specific capacitance of 316 F g −1 .…”

“…It was consistently stable during the more than 1000 cycles and exhibited a high specic capacitance of 316 F g −1 . 291 Furthermore, Phachwisoot et al proposed the catalytic hydrothermal processing of cassava rhizome coupled with ZnCl 2 and melamine co-activation to produce levulinic acid and porous N-doped activated hydrochar material for SC application (for details, see Fig. 8).…”

“…It was consistently stable during the more than 1000 cycles and exhibited a high specific capacitance of 316 F g −1 . 291…”