Valorization of biodigestor plant waste in electrodes for supercapacitors and microbial fuel cells

Synthesis of Sustainable Lignin Precursors for Hierarchical Porous Carbons and Their Efficient Performance in Energy Storage Applications

Lignin-derived porous carbons have great potential for energy storage applications. However, their traditional synthesis requires highly corrosive activating agents in order to produce porous structures. In this work, an environmentally friendly and unique method has been developed for preparing lignin-based 3D spherical porous carbons (LSPCs). Dropwise injection of a lignin solution containing PVA sacrificial templates into liquid nitrogen produces tiny spheres that are lyophilized and carbonized to produce LSPCs. Most of the synthesized samples possess excellent specific surface areas (426.6-790.5 m2/g) along with hierarchical micro- and mesoporous morphologies. When tested in supercapacitor applications, LSPC-28 demonstrates a superior specific capacitance of 102.3 F/g at 0.5 A/g, excellent rate capability with 70.3% capacitance retention at 20 A/g, and a commendable energy density of 2.1 Wh/kg at 250 W/kg. These materials (LSPC-46) also show promising performance as an anode material in sodium-ion batteries with high reversible capacity (110 mAh g-1 at 100 mA g-1), high Coulombic efficiency, and excellent cycling stability. This novel and green technique is anticipated to facilitate the scalability of lignin-based porous carbons and open a range of research opportunities for energy storage applications.

Giving New Life to Waste Cigarette Butts: Transformation into Platinum Group Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Acid, Neutral and Alkaline Environment

Following the core theme of a circular economy, a novel strategy to upcycle cigarette butt waste into platinum group metal (PGM)-free metal nitrogen carbon (M-N-C) electrocatalysts for oxygen reduction reaction (ORR) is presented. The experimental route was composed of (i) the transformation of the powdered cigarette butts into carbonaceous char via pyrolysis at 450 °C, 600 °C, 750 °C and 900 °C, (ii) the porosity activation with KOH and (iii) the functionalization of the activated chars with iron (II) phthalocyanine (FePc). The electrochemical outcomes obtained by the rotating disk electrode (RRDE) technique revealed that the sample pyrolyzed at 450 °C (i.e., cig_450) outperformed the other counterparts with its highest onset (Eon) and half-wave potentials (E1/2) and demonstrated nearly tetra-electronic ORR in acidic, neutral and alkaline electrolytes, all resulting from the optimal surface chemistry and textural properties.

Fe, N, S co-doped cellulose paper carbon fibers as an air-cathode catalyst for microbial fuel cells

The heteroatoms and transition metal co-doped carbon-based catalysts are an important way to improve the catalytic activity of oxygen reduction reaction (ORR). Herein, we reported a facile method to obtain iron, nitrogen, and sulfur co-doped cellulose paper carbon fibers as catalysts (Fe-N-S/CFs) for ORR in microbial fuel cells (MFCs) with the adsorption recovery of Congo red molecules from dye wastewater. The thermal treatment promoted the etching of carbon surface by ferric ions, resulting in increased surface roughness for forming the defective carbon structure. The rich active species and defective carbon formed on the etched surface to enhance the electroactive surface area and effective sites. Fe-N-S/CFs catalysts achieved high half-wave potential due to the synergy effect between chemical components and defect structures. The assembled single-chamber air cathode MFC gained a high maximum power density of 1773 ± 40 mW m^-2 versus Pt/C MFC of 1325 ± 94 mW m^-2. This work provides a strategy for recovering dye molecules from wastewater to prepare non-precious metal catalysts for enhancing ORR activity.

Biomass Hierarchical Porous Carbonized Typha angustifolia Prepared by Green Pore-Making Technology for Energy Storage

The cost-effective biomass-derived carbon with high electrochemical performance is highly desirable for the sustainable development of advanced energy storage devices. In this manuscript, Typha angustifolia with a large output and loose porous characteristics was selected as the raw material of biomass. In the synthesis process, KHCO₃, which is more environmentally friendly, is used as a pore-forming agent, and the low-cost, easy-to-clean fluxing agent NaCl is used to assist the pore-forming process. Based on the analysis of thermogravimetric-infrared test results, the calcination procedure of porous carbon was designed reasonably, so that the functions of the pore-forming agent and fluxing agent could be fully exerted. Its high electrochemical performance is attributed to combined contributions from high surface area and hierarchical porous structures. The as-prepared carbon also showed an outstanding capacitance of 317.2 F/g at a current density of 1 A g^-1 and a high capacitance retention of over 97.83% after 5000 cycles at a current density of 4 A g^-1. This work provides an outstanding renewable candidate and a feasible route design strategy for the fabrication of high-performance electrodes.

Hardwood Kraft lignin-derived carbon microfibers with enhanced electrochemical performance

It is of great challenge to prepare lignin-derived carbon microfibers with suitable graphite crystallites due to the volatilization of incorporated polymers. In this work, we proposed a simple method for the construction of graphite crystallites based on the regulation of the hydrogen-bonding interaction between hardwood Kraft lignin (HKL) and poly(m-phenylene isophthalamide) (PMIA). The strong hydrogen-bonding interaction demonstrated by the results of TG, FTIR, XPS, Raman and XRD increased the graphite crystal size and perfected the crystal structure of HKL-based carbon microfibers, which further enhanced the electrochemical performance of HKL/PMIA-based carbon microfibers electrodes, especially for the increase of capacitance and cycle performance and the decrease of charge transfer resistance. The specific capacitance, energy density and power density of P2H2-based (HKL/PMIA = 1:1) carbon microfibers electrode were up to 190.8 F g^-1, 34.4 Wh kg^-1 and 540 W kg^-1 at a current density of 0.5 A g^-1, respectively, which were comparable to or even higher than those of lignin composites-based carbon fibers electrodes. This work reveals the relationship between hydrogen-bonding interaction and crystalline structure, which can be further considered in the preparation of lignin-based carbon fibers electrodes.

Lignin-Based/Polypyrrole Carbon Nanofiber Electrode With Enhanced Electrochemical Properties by Electrospun Method

Tailoring the structure and properties of lignin is an important step toward electrochemical applications. In this study, lignin/polypyrrole (PPy) composite electrode films with microporous and mesoporous structures were designed effectively by electrostatic spinning, carbonization, and in situ polymerization methods. The lignin can not only reduce the cost of carbon fiber but also increase the specific surface area of composite films due to the removal of carbonyl and phenolic functional groups of lignin during carbonization. Besides, the compact three-dimensional (3D) conductive network structures were constructed with PPy particles densely coated on the lignin nanofibers, which was helpful to improve the conductivity and fast electron transfer during the charging and discharging processes. The synthesized lignin carbon fibers/PPy anode materials had good electrochemical performance in 1 M H2SO4 electrolyte. The results showed that, at a current density of 1 A g−1, the lignin carbon nanofibers/PPy (LCNFs/PPy) had a larger specific capacitance of 213.7 F g−1 than carbon nanofibers (CNFs), lignin carbon nanofibers (LCNFs), and lignin/PPy fiber (LPAN/PPy). In addition, the specific surface area of LCNFs/PPy reached 872.60 m2 g−1 and the average pore size decreased to 2.50 nm after being coated by PPy. Therefore, the independent non-binder and self-supporting conductive film is expected to be a promising electrode material for supercapacitors with high performance.