Integrated hierarchical porous lignin-based carbon electrode for boosting membrane-free capacitive deionization areal adsorption capacity.

The development of high value-added lignin-based functional porous carbon electrodes with excellent properties from sustainable industry lignin powder remains a challenge. This work aims to create robust, binder-free, conductive additives-free, and current collector-free monolithic porous carbon electrodes using industrial lignin powder for membrane-free capacitive deionization (CDI). The material exhibits high mechanical strength, hierarchical porosity structure, large uniform size, and thickness of just a few millimetres (<2.6 mm). In a three-electrode supercapacitor system, the areal specific capacitance of CLCA300-3-1.0 reaches 5.03-1.02 F cm-2 when the scan rate between 1 and 20 mV s-1 in 1 M NaCl solution. As CDI electrodes, the charge efficiency of CLCA300-3-1.0 at different voltages of 1.2 V, 1.4 V and 1.6 V is 0.53, 0.72 and 0.71, respectively. The energy consumption of CLCA280-3-1.0, CLCA300-3-1.0 and CLCA320-3-1.0 tested at 1.2 V are 3.27, 3.40 and 3.25 Wh m-3, respectively. In addition, with thickness increasing to 1.5 mm, the developed CLCA300-3-1.5 electrode exhibits an areal adsorption capacity of 0.46 mg cm-2, and relative highly capacity retention of 84.78 % after 70 cycles. The impressive desalination performance is attributed to the well-designed hierarchical porosity, superhydrophilicity and robust monolithic structure.

Construction of self-supporting ultra-micropores lignin-based carbon nanofibers with high areal desalination capacity.

Lignin is a renewable biomacromolecule that can be used as precursors for carbon materials. In this work, highly flexible lignin-based carbon nanofibers with abundant ultra-micropores are constructed via electrospinning, oxidative stabilization and carbonization. The results indicate that replacing PAN with 80 % lignin is feasible in regulating ultra-micropores. The synthesized L4P1-CNFs possess many attractive properties (e.g., pore size distribution, electrochemical and deionization property) compared with that produced from other non-renewable precursors or more-complexed processes. It shows excellent electrochemical double-layer capacitance in 6 M KOH (233 to 162 F g-1 at 0.5 to 5 A g-1) and 1 M NaCl (158 to 82 F g-1 at 0.5 to 5 A g-1) electrolytes. Upon assembling into CDI cells, the average salt adsorption rate could reach 1.79 mg g-1 min-1 at 1.2 V and 3.32 mg g-1 min-1 at 2 V in 500 mg L-1. Benefiting from the excellent flexibility, we innovatively stack four layers of L4P1-CNFs to improve the areal electrosorption capacity to 0.0817 mg cm-2 at 500 mg L-1, significantly higher than that of traditional carbon-based electrodes. The good desalination property makes lignin-based carbon nanofibers ideal for practical, low-cost capacitive deionization applications.

Simple, additive-free, extra pressure-free process to direct convert lignin into carbon foams.

To achieve lignin valorization, we reported a simple method to direct covert lignin into carbon foam materials in this work. Unlike multiple steps required to fabricate traditional carbon foams from most of other precursors (often non-renewable), the approach herein required solely heating for carbon production. We found that the intrinsic features of lignin render the formation of lignin block meanwhile generate the porous structure under the invented heating course. Three key factors including glass transition temperature, crosslinking ability, and thermal stability of lignin were identified to determine the successful fabrication of lignin foam (i.e., precursor of carbon foam). Upon tuning the heating profile or fractionating the lignin, lignin foam with different morphologies and properties were obtained. After carbonization, the selected lignin-derived carbon foams possessed well porous structures with bulk densities of 0.52 or 0.62 g cm-3, superior integrity with strength properties of around 10 MPa, BET surface areas of 143.29 or 325.86 m2 g-1, and many other attractive properties. This work is expected to stimulate further seek of lignin valorization in carbon foam production.

Lignin-based carbon nanofibe rs: Morphologies, properties, and features as substrates for pseudocapacitor electrodes.

In this work, lignin-based carbon nanofibers (LCNFs) were for the first time served as substrate for in-situ electrodeposition of polyaniline (PANI) and tested as pseudocapacitor. Two LCNFs with different lignin ratios were designed to distinguish their morphology and structural properties. Next, PANI deposition mechanisms on both LCNFs were investigated and the electrochemical performance of the resulting LCNF/PANIs were evaluated. It was found although LCNF2 was composed of less uniform nanofibers due to more presence of lignin in precursor dope, it had higher tensile strength/modulus than LCNF1 (strength: 34.3MPa to 24.2 MPa; Modulus: 2.40 GPa to 1.45GPa) and was more cost-effective. Particularly, the beaded fibers on LCNF2 contributes to the deposition of PANI with higher specific mass capacitance (612.8 F g-1 to 547.0 F g-1). Upon assembling into solid-state supercapacitors, the Cm of LCNF2/PANI device was determined to be 229 F g-1 and the maximum energy density was 11.13Wh kg-1 at a power density of 0.08 kW kg-1. This work showed LCNF produced from renewable and low-cost lignin could be directly used as substrate for PANI deposition. Moreover, the composition in spinning dope played an important role in determining the performances of resulting pseudocapacitors.

Towards producing high-quality lignin-based carbon fibers: A review of crucial factors affecting lignin properties and conversion techniques.

The production of low-cost and high-quality carbon fibers (CFs) from biorenewable lignin precursors has been of worldwide interest for decades. Although numerous works have been reported and the proposed "1.72 GPa/172 GPa" target set by the Department of Energy (DOE) has been closely met in a few studies, most lignin-based CFs (LCFs) have poor strength properties compared to industrial PAN (polyacrylonitrile)-based CFs. The production of LCFs involves several steps, and the final quality of LCFs is governed by both lignin's properties and the manufacturing processes. Therefore, understanding the key factors of producing high quality LCF is of high importance. In this review, we firstly outlined several lignin's properties (e.g., impurities, thermal properties, molecular structure) that may play important role in determining its processability and suitability as carbon fiber precursor. Secondly, conversion strategies include spinning, stabilization and carbonization, and corresponding parameters influencing the final quality of LCF are comprehensively analyzed. Last, additional characterization methods are proposed as a means to facilitate analyzing of lignin and LCF. This review attempts to provide insights towards high-quality LCF production from both material and manufacturing aspects.

Lignin-derived 3D porous graphene on carbon cloth for flexible supercapacitors.

In this work, we reported a new method to fabricate flexible carbon-based supercapacitor electrodes derived from a commercialized and low-cost lignin. The fabrication process skips traditional stabilization/carbonization/activation for lignin-based carbon production. Also, the process reported here was green and facile, with minimum solvent use and no pretreatment required. Characterization of the lignin showed that it has common properties among all types of lignin. The lignin was impregnated on carbon cloth and then subjected to direct laser writing to form the desired electrodes (LLC). The results showed that lignin was successfully bonded to carbon cloth. The LLC has a good porous carbon structure with a high I G/I D ratio of 1.39, and a small interlayer spacing d 002 of 0.3436 nm, which are superior to most of the reported lignin-based carbons. Although not optimized, the fabricated LLC showed good supercapacitance behavior with an areal capacitance of 157.3 mF cm-2 at 0.1 mA cm-2. In addition, the superior flexibility of LLC makes it a promising electrode that can be used more widely in portable devices. Conceptually, this method can be generalized to all types of lignin and can define intriguing new research interests towards lignin applications.

Tunable Wettability of Biodegradable Multilayer Sandwich-Structured Electrospun Nanofibrous Membranes.

This research aims to develop multilayer sandwich-structured electrospun nanofiber (ENF) membranes using biodegradable polymers. Hydrophilic regenerated cellulose (RC) and hydrophobic poly (lactic acid) (PLA)-based novel multilayer sandwich-structures were created by electrospinning on various copper collectors, including copper foil and 30-mesh copper gauzes, to modify the surface roughness for tunable wettability. Different collectors yielded various sizes and morphologies of the fabricated ENFs with different levels of surface roughness. Bead-free thicker fibers were collected on foil collectors. The surface roughness of the fine fibers collected on mesh collectors contributed to an increase in hydrophobicity. An RC-based triple-layered structure showed a contact angle of 48.2°, which is comparable to the contact angle of the single-layer cellulosic fabrics (47.0°). The polar shift of RC membranes on the wetting envelope is indicative of the possibility of tuning the wetting behavior by creating multilayer structures. Wettability can be tuned by creating multilayer sandwich structures consisting of RC and PLA. This study provides an important insight into the manipulation of the wetting behavior of polymeric ENFs in multilayer structures for applications including chemical protective clothing.