Performance and Economic Analysis of Organosolv Softwood and Herbaceous Lignins to Activated Carbons as Electrode Materials in Supercapacitors

Abstract

In this work, yellow pine (YP, softwood) and switchgrass (SG, grass) lignins were extracted as a coproduct of an organosolv γ-valerolactone (GVL) biorefinery that also produces biofuels and furfural. The extracted lignins were converted to carbon precursors for synthesizing porous activated carbon electrodes for high energy-density supercapacitors. This research details the impact of lignin composition on the derived porous structures and electrochemical properties of activated carbons. Lignin precursors with various syringyl (S) to guaiacyl (G) contents were characterized using 31P nuclear magnetic resonance (NMR) and two-dimensional 1H‒13C NMR. A two-step activation process, using steam and carbon dioxide as the activating agents, enabled the formation of porous carbons structures with high surface area. The capacitive behavior of supercapacitors was systematically characterized by cyclic voltammetry, charge-discharge cycling, and electrochemical impedance spectroscopy. The specific capacitance of YP and SG capacitors reached 367 and 221 F g−1, respectively. Both types of capacitors demonstrated remarkably stable capacitance (capacitance retention >90%) along with excellent Coulombic efficiency (>99%) over 10,000 cycles. Compared to SG electrode, the better electrochemical performance achieved with YP electrodes was mainly due to shorter diffusion path, improved ionic mobility, and increased active surface area. The inexpensive lignin-based porous electrodes synthesized in this work can be used for various electrochemical devices for improved performance, decreased cost, and enhanced durability. This work also demonstrates that the selection of feedstock and appropriate processing conditions can tailor the structure of carbon composites for targeted applications. Techno-economic analysis indicates that YP and SG activated carbons can be produced at a minimum selling price of $8,493 and $6,670 per ton, respectively, which is competitive with the commercially available supercapacitor-grade activated carbons.

Analysis of Single-Step Pretreatments for Lignocellulosic Platform Isolation as the Basis of Biorefinery Design

“…Pretreatments such as organosolv involve solvents that increase the energy requirements and operating costs of the process, decreasing its economic viability. The economic feasibility of organosolv schemes has been widely reported for lignin extraction at the pilot scale [ 69 ]. The kraft and alkaline processes are used at the industrial scale for removing lignin from woody biomass for pulp and paper production.…”

“…Although dilute acid pretreatment has been widely discussed in biotechnological applications, its implementation at the industrial scale has been slowed down. These delays are largely due to the generation and accumulation of inhibitory compounds and the high corrosion of processing units and piping [ 69 ]. Therefore, TRL must be analyzed from an operational and design perspective with techno-energetic and economic considerations.…”

High performance bio-supercapacitor electrodes composed of graphitized hemicellulose porous carbon spheres

“…Therefore, research on electrode materials has been a hot topic ( Walters et al, 2021 ; Yu et al, 2021 ). Currently, porous carbon spheres are excellent candidates for electrode materials due to their physical morphology, chemical resistance, and well-developed porous structures ( Veerakumar et al, 2020 ; Song et al, 2021 ; Liu et al, 2022 ; Yu et al, 2022 ). The regular spherical shape reduces the resistance of electrolyte diffusion, and the space between the spheres makes the electrode accessible to the electrolyte ( Chen et al, 2014 ; Oschatz et al, 2015 ; Mutuma et al, 2019 ).…”

“…Recently, a growing body of research has focused on cheap and renewable biomass resources as supercapacitive electrolytic feedstocks ( Vijayakumar et al, 2019 ; Zhang et al, 2019 ; Xu et al, 2020 ; Peng et al, 2022 ). A multitude of low molecular weight carbohydrates such as lignin, chitosan, glucose, fructose, sucrose, xylose, have been explored to produce PCSs by mild hydrothermolysis ( Saha et al, 2014 ; Xu et al, 2018 ; Gao et al, 2021 ; Hwang et al, 2022 ; Yu et al, 2022 ). But a paucity of studies has reported preparation of porous carbon spheres directly from high molecular weight carbohydrates such as cellulose and hemicelluloses ( Wang and Shi, 2015 ; Hwang et al, 2022 ).…”