Direct Microwave Conversion from Lignin to Micro/Meso/Macroporous Carbon for High‐Performance Symmetric Supercapacitors

Lignin Derived Porous Carbons: Synthesis Methods and Supercapacitor Applications

Lignin, one of the renewable constituents in natural plant biomasses, holds great potential as a sustainable source of functional carbon materials. Tremendous research efforts have been made on lignin-derived carbon electrodes for rechargeable batteries. However, lignin is considered as one of the most promising carbon precursors for the development of high-performance, low-cost porous carbon electrode materials for supercapacitor applications. Yet, these efforts have not been reviewed in detail in the current literature. This review, therefore, offers a basis for the utilization of lignin as a pivotal precursor for the synthesis of porous carbons for use in supercapacitor electrode applications. Lignin chemistry, the synthesis process of lignin-derived porous carbons, and future directions for developing better porous carbon electrode materials from lignin are systematically reviewed. Technological hurdles and approaches that should be prioritized in future research are presented.

Lignocellulosic Biomass-Derived Carbon Electrodes for Flexible Supercapacitors: An Overview

With the increasing demand for high-performance electronic devices in smart textiles, various types of flexible/wearable electronic device (i.e., supercapacitors, batteries, fuel cells, etc.) have emerged regularly. As one of the most promising wearable devices, flexible supercapacitors from a variety of electrode materials have been developed. In particular, carbon materials from lignocellulosic biomass precursor have the characteristics of low cost, natural abundance, high specific surface area, excellent electrochemical stability, etc. Moreover, their chemical structures usually contain a large number of heteroatomic groups, which greatly contribute to the capacitive performance of the corresponding flexible supercapacitors. This review summarizes the working mechanism, configuration of flexible electrodes, conversion of lignocellulosic biomass-derived carbon electrodes, and their corresponding electrochemical properties in flexible/wearable supercapacitors. Technology challenges and future research trends will also be provided.

Lignocellulose-based free-standing hybrid electrode with natural vessels-retained, hierarchically pores-constructed and active materials-loaded for high-performance hybrid oxide supercapacitor

Lignocellulose including cellulose, lignin, and hemicellulose could be extracted from wood, and has been used to prepare carbon electrode. However, complicated extraction greatly increases preparation cost. To achieve maximum utilization of lignocellulose and avoid complicated extraction, wood with porous structure and good mechanical strength is used as carbon precursor. Additionally, chemical activation is commonly used to create micropores to provide high capacitance, but it brings in natural structure destruction, and generation of wastewater during pickling. Moreover, to achieve desirable energy density, multi-step strategy with long duration is required for loading active materials on carbonized lignocellulose (CL). Herein, a one-step method is developed to prepare a free-standing hybrid CL electrode (CLE) by using Lewis acid in three aspects: (1) as structure protection agent, (2) as activating agent, (3) as active materials donor, which bypasses pickling and further avoids the generation of wastewater. Additionally, natural vessels in wood can not only provide large space for active materials loading, but also act as rapid ions diffusion way, simultaneously confining active materials detachment. Benefiting from the synergistic effect of porous structure and Lewis acid, this work not only makes full utilization of lignocellulose, but also makes CLE exhibit excellent performance in hybrid oxide supercapacitor.

Pyrolysis of Biomass Impregnated With Ammonium Dihydrogen Phosphate for Polygeneration of Phenol and Supercapacitor Electrode Material

A new method was proposed for polygeneration of phenol and supercapacitor electrode material from pyrolysis of biomass impregnated with ammonium dihydrogen phosphate (NH₄H₂PO₄). The pyrolysis experiments were executed to demonstrate the product distributions under different NH₄H₂PO₄-to-poplar (PA-to-PL) ratios and pyrolysis temperatures in a lab-scale device. The results revealed that the phenol yield attained its optimal value of 4.57 wt% with a satisfactory selectivity of 20.09% at 500°C under PA-to-PL ratio of 0.6. The pyrolytic solid product obtained at this condition was then subjected to high temperature activation directly without additional activators to prepare N and P co-doped activated carbon (NPAC) as supercapacitor. The physicochemical analysis of NPAC showed that the N and P contents in NPAC reached 3.75 and 3.65 wt%, respectively. The electrochemical experiments executed in a three-electrode system indicated that the NPAC exhibited promising electrochemical performance with a satisfactory capacitance of 181.3 F g^-1 at 1 A g^-1.