Heteroatom-doped and graphitization-enhanced lignin-derived hierarchically porous carbon via facile assembly of lignin-Fe coordination for high-voltage symmetric supercapacitors

Lignin-derived carbon materials are widely used as electrode materials for supercapacitors. However, the electrochemical performance of these materials is limited by the surface chemistry and pore structure characteristics. Herein, a novel and sustainable strategy was proposed to prepare heteroatom-doped lignin-derived carbon material (Fe-NLC) with well-developed pore size distributions and enhanced graphitization structure via a facile lignin-Fe coordination method followed by carbonization. During carbonization, Fe3+ in lignin-metal complexes evolve into nanoparticles, which act as templates to introduce porous structures in carbon materials. Also, the lignin-Fe coordination structure endows the material with a higher graphitization during carbonization, thereby improving the structural properties of the carbon materials. Due to the removal of Fe3O4 template, the obtained Fe-NLC possessed reasonable pore distribution and nitrigen/oxygen (N/O) functional groups, which can improve the wettability of materials and introduce pseudocapacitance. Accordingly, Fe-NLC possesses a notable specific capacitance of 264 F/g at 0.5 A/g. Furthermore, a symmetric supercapacitor Fe-NLC//Fe-NLC with a high voltage window (1.8 V) was constructed. The symmetric supercapacitor exhibits a maximum energy density of 15.97 Wh/kg at 450 W/kg, demonstrating well application prospects. This paper proposes a novel approach for preparing carbon materials via lignin-metal coordination to provide an alternative way to explore sustainable and low-cost energy storage materials.

Oxygen-enriched pitch-derived hierarchically porous carbon toward boosted zinc-ion storage performance

The lack of cathode materials with satisfactory Zn2+ storage capability substantially hinders the realization of high-performance aqueous zinc-ion hybrid capacitors (ZHCs). Herein, we propose a facile KMnO4 template-assisted KOH activation strategy to prepare a novel oxygen-enriched hierarchically porous carbon (HPC-1-4). This strategy efficiently converts coal tar pitch (CTP) into a well-tuned carbon material with a large specific surface area of 3019 m2 g-1 and a high oxygen content of 9.20 at%, which is conducive to providing rich active sites, rapid charge transport, and appreciable pseudocapacitance for Zn-ion storage. Thus, the as-fabricated HPC-1-4-based aqueous ZHC exhibits prominent performance, including a high gravimetric capacity (206.7 mAh g-1 at 0.25 A g-1), a remarkable energy density (153.4 Wh kg-1 at 184.2 W kg-1), and an impressive power output (15240 W kg-1 at 63.5 Wh kg-1). In-depth ex-situ characterizations indicate that the excellent electrochemical properties of ZHCs are due to the synergistic effect of the Zn2+ adsorption mechanism and reversible chemisorption. In addition, the assembled quasi-solid-state device demonstrates excellent electrochemical stability of up to 100% capacity retention over 50000 cycles, accompanied with a desirable energy density of 115.6 Wh kg-1. The facile preparation method of converting CTP into carbonaceous functional materials has advanced the development of efficient and eco-friendly energy storage technologies.

Baking-inspired pore regulation strategy towards a hierarchically porous carbon for ultra-high efficiency cationic/anionic dyes adsorption

Converting waste resource into porous carbon toward contaminant capturing is a crucial strategy for realizing "treating waste with waste". Inspired by bread baking process, the soybean meal activated carbon (SAC) with multimodal pore structures was developed via thermally remodeling the pores of waste soybean meal. The obtained SAC-3-800 has ultra-high specific surface area (3536.952 m2/g), as well as a hierarchically porous structure. SAC-3-800 exhibits extremely high adsorption capacity for methylene blue (MB) (3015.59 mg/g), methyl orange (MO) (6486.30 mg/g), and mixed dyes (8475.09 mg/g). The hierarchically porous structure enabled fast adsorption kinetics of SAC-3-800 for MB and MO (∼30 min). Additionally, SAC-3-800 shows excellent dynamic adsorption and regeneration performance, exhibiting great potential for industrial applications. This work showcases a feasible method for synthesizing hierarchically porous carbon with outstanding adsorption performance that can simultaneously achieve efficient treatment of dye-wastewater and value-added utilization of waste resources.

A lignin-derived N-doped carbon-supported iron-based nanocomposite as high-efficiency oxygen reduction reaction electrocatalyst

Fuel cells are a promising renewable energy technology that depend heavily on noble metal Pt-based catalysts, particularly for the oxygen reduction reaction (ORR). The discovery of new, efficient non-precious metal ORR catalysts is critical for the continued development of cost-effective, high-performance fuel cells. The synthesized carbon material showed excellent electrocatalytic activity for the ORR, with half-wave potential (E1/2) and limiting current density (JL) of 0.88 V and 5.10 mA·cm-2 in alkaline electrolyte, respectively. The material has a Tafel slope of (65 mV dec-1), which is close to commercial Pt/C catalysts (60 mV dec-1). Moreover, the prepared materials exhibited excellent performance when assembled as cathodes for zinc-air batteries. The power density reached 110.02 mW cm-2 and the theoretical specific capacity was 801.21 mAh g-1, which was higher than that of the Pt/C catalyst (751.19 mAh g-1). In this study, with the assistance of Mg5(CO3)4(OH)2·4H2O, we introduce an innovative approach to synthesize advanced carbon materials, achieving precise control over the material's structure and properties. This research bridges a crucial gap in material science, with potential applications in renewable energy technologies, particularly in enhancing catalysts for fuel cells.

Smartphone-based electrochemical sensor for cost-effective, rapid and on site detection of chlorogenic acid in herbs using biomass-derived hierarchically porous carbon synthesized by a soft-hard dual template method

To achieve excellent germplasm resource screening and ensure the quality control of herbal tea raw material, it is important to establish a cost-effective, rapid, and on site quantitative detection method for their bioactive constituents. We developed a smartphone-operated sensor for electrochemical detection of chlorogenic acid (CGA) using hierarchically porous carbon (DSiFPC), synthesized through a soft-hard dual template strategy with tannin acid as a carbon source, silica colloid as a hard template, and Pluronic F127 as a soft template. The DSiFPC modified glassy carbon electrode sensor showed excellent electrocatalytic ability towards CGA, with a wide linear range of 0.03-1 μM and a low limit of detection of 6.2 nM. It was successfully applied for detecting CGA in dried flowers of Lonicera japonica. Furthermore, a portable sensor utilizing a DSiFPC modified screen-printed electrode was employed for on site detection of CGA in fresh Eucommia ulmoides leaves, yielding satisfactory recoveries.

Coexisting Fe single atoms and nanoparticles on hierarchically porous carbon for high-efficiency oxygen reduction reaction and Zn-air batteries

Fe single-atom catalysts still suffer from unsatisfactory intrinsic activity and durability for oxygen reduction reaction (ORR). Herein, the coexisting Fe single atoms and nanoparticles on hierarchically porous carbon (denoted as Fe-FeN-C) are prepared via a Zn5(OH)6(CO3)2-assisted pyrolysis strategy. Theoretical calculation reveals that the Fe nanoparticles can optimize the electronic structures and d-band center of Fe active center, hence reducing the reaction energy barrier for enhancing intrinsic activity. The Zn5(OH)6(CO3)2 self-sacrificial template not only can promote the formation of Fe single atoms, but also contributes to the construction of microporous/mesoporous/macroporous structures. Therefore, the obtained Fe-FeN-C exhibits impressive ORR activity with a half-wave potential of 0.921 V, which far exceeds Pt/C. With Fe-FeN-C as the cathode catalyst, the assembled Zn-air batteries delivered a maximum power density of 206 mW cm-2 and a long-cycle life over 400 h.

Versatile potassium vanadium fluorophosphate (KVPO4F) composites as Dual-Function cathode and anode materials for Potassium-Ion hybrid capacitors

Potassium-based energy storage has emerged as a promising alternative for advanced energy storage systems, driven by the abundance of potassium, fast ion migration, and low standard electrode potential. Hybrid capacitors, which combine the desirable characteristics of batteries and supercapacitors, offer a compelling solution for efficient energy storage. In this study, we present the development of versatile composite materials, specifically potassium vanadium fluorophosphate (KVPO4F) composites, utilizing a sol-gel method. These composites enable tunable potassium storage and charge transport kinetics within regulated voltage windows, serving as both cathode and anode materials. The anode composite, composed of KVPO4F and hierarchical porous carbon (HPC), exhibited exceptional stability over 400 cycles within a low-voltage window. On the other hand, the cathode composite, consisting of battery-like KVPO4F and physisorption activated carbon (AC), demonstrated great potential as a cathode material, striking a balance between specific energy and cycle life within a regulated high-voltage window. By integrating KVPO4F/C as the anode and KVPO4F/AC as the cathode, we successfully created potassium-ion hybrid capacitors (PIHCs) that showcased an impressive capacity retention of 83% after 10,000 cycles within a high voltage window of 0.5-4.3 V. Furthermore, to explore the application of these materials in miniaturized energy storage, we fabricated potassium-ion micro hybrid capacitors (PIMHCs) with interdigitated electrodes. These devices exhibited a high areal energy density of 18.8 μWh cm-2 at a power density of 111.6 μW cm-2, indicating their potential for compact energy storage systems. The results of this study demonstrate the versatility and efficacy of the developed KVPO4F composite materials, highlighting their potential for future advancements in potassium-based energy storage technologies.

Novel metal-lignin assembly strategy for one-pot fabrication of lignin-derived heteroatom-doped hierarchically porous carbon and its application in high-performance supercapacitor

The conversion of renewable lignin with low-cost and high carbon content properties into porous carbon materials for supercapacitor applications has caught considerable interest. Herein, two dimensional lignin-derived carbon nanosheets (N-LHPC) with hierarchically porous structures were facilely synthesized via a novel metal-lignin assembly strategy and their performances for supercapacitor applications were investigated. During the carbonization process, the uniformly distributed Zn facilitates the coordinating development of micropores structure and the generated MgO embedded in the carbon matrix acts as a template to produce mesoporous structure after acid washing. Moreover, the melamine addition promotes the development of mesopores by formation of lamellae structure and realizes the N doping in the carbon materials. Therefore, the obtained N-LHPC presents an excellent specific capacitance of 235.75 F/g at 0.5 A/g owing to its hierarchical pore structure as well as the N/O functional groups. Moreover, at the power density of 450 W/kg, the N-LHPC achieves a maximum energy density of 14.75 Wh/kg, showing great application potential in energy storage. The metal-lignin assembly strategy followed by N-doping proposed in this paper provides N-LHPC materials with hierarchical nanostructure, good electron/ion transfer properties, and abundant pseudocapacitive active species, which improve the capacitance performances of the N-LHPC.

Magnesium lignosulfonate-derived N, S co-doped 3D flower-like hierarchically porous carbon as an advanced metal-free electrocatalyst towards oxygen reduction reaction

The development of metal-free electrocatalytic materials that are economical, friendly to the environment, and efficiency towards the oxygen reduction reaction (ORR) is of significant interest. Hence, this paper synthesizes nitrogen and sulfur co-doped three-dimensional magnesium lignosulfonate (MLS-derived) flower-like hierarchical porous carbon (NSLPC) materials by a simple and green method. The synthesized NSLPC uses magnesium lignosulfonate as the sulfur source and carbon precursor, melamine as nitrogen source, MgO as hard template, and ZnCl₂ as the activator. We also investigated the effect of the ratio of MgO to ZnCl₂ on the catalyst performance. When the ratio of MgO to ZnCl₂ is 10:0.5, NSLPC-1005 possesses the highest ORR activity with an enormous surface area (1752.54 m² g^-1), abundant active sites, and a hierarchical porous network structure. In alkaline media, NSLPC-1005 has an initial potential of 0.97 V, as well as an excellent half-potential of 0.86 V (vs. Hg/HgO), and an ultimate current density of 5.35 mA cm^-2. It exhibits attractive ORR performance as well as outstanding cyclic stability that are comparable to commercial Pt/C electrocatalysts. This research developed an effective approach to synthesize metal-free carbon materials with high activity and long-term durability as electrocatalysts, which have a promising application in sustainable energy conversion technology.

Triple combination of natural microbial action, etching, and gas foaming to synthesize hierarchical porous carbon for efficient adsorption of VOCs

Fungi residue, vinasse, and biogas residue differ from general biomass waste due to natural microbial action. Microbial fermentation helps create natural channels for the permeation of activators and produces proteins for natural nitrogen doping. Inspired by these advantages on porous carbon synthesis, this study adopted dual activators of KOH and KHCO₃ to synthesize porous carbon with different pore ratios for efficient adsorption of volatile organic compounds (VOCs). The fungi residue possessed the least lignin due to the most severe microbial action, contributing to the best pore structures after activation. The etching effect from potassium compounds and gas foaming from the carbonate decomposition contributed to creating hierarchical porous carbon with ultra-high surface area, ca. 1536.8-2326.5 m²/g. However, KHCO₃ addition also caused nitrogen erosion, such that lower adsorption capacity was attained even with a higher surface area when the mass ratio of KOH/KHCO₃ decreased from 2.5:0.5 to 2:1. The maximum adsorption capacities of chlorobenzene (CB) and benzene (PhH) reached 594.0 and 394.3 mg/g, respectively. Pore structure variations after adsorption were evaluated by freeze treatment to discover the adsorption mechanism. The surface area after CB and PhH adsorption decreased 40.3% and 34.5%, respectively. Most of the mesopores might transform into micropores due to the mono/multilayer stacking of adsorbates. The VOC adsorption kinetics were simulated by the Pseudo-first- and -second-order models and Y-N model. This paper provides a new approach for high-value biomass waste utilization after microbial action to synthesize efficient adsorbents for VOCs.

Transforming polystyrene waste into 3D hierarchically porous carbon for high-performance supercapacitors

Polystyrene (PS) is usually discarded as a solid waste after a short lifespan. Thus the disposal of waste PS is an inevitably worldwide issue because of their stable and non-biodegradable nature. Herein, a facile method was proposed to carbonize PS waste into novel three-dimensional (3D) hierarchically porous carbon using Fe₂O₃ particles as both catalyst and template. Furthermore, KOH activation was applied to generate microporous and mesopores on the wall of macropores. As a result, the obtained 3D hierarchically porous carbon exhibits a high specific capacitance of 284.1 F g^-1 at 0.5 A g^-1 and good rate performance of 198 F g^-1 at 20 A g^-1 in a three-electrode device. Moreover, the assembled symmetrical capacitor displays a high energy density of 19.2 W h kg^-1 at the power density of 200.7 W kg^-1 in aqueous electrolyte. Therefore, the present research develops a sustainable way to recycle waste plastics into 3D hierarchically porous carbon for supercapacitors.

Designing transition metal alloy nanoparticles embedded hierarchically porous carbon nanosheets as high-efficiency electrocatalysts toward full water splitting

Developing high-efficiency catalysis electrodes towards both HER (hydrogen evolution reaction) and OER (oxygen evolution reaction) is critical to the popularity and practical application of devices for conversion and storage of clean and renewable hydrogen energy by overall water splitting. In this paper, a series of transition metal alloy nanoparticles embedded hierarchically porous carbon nanosheets (denoted as Fe_xCo_y@PCNSs) have been successfully designed and synthesized. After optimizing the metallic contents in Fe_xCo_y alloy, Fe₃Co₇@PCNSs displays superior water electrolysis performances compared to other control samples and previously reported non-noble metal catalysts. This advance is mainly due to the synergistic effect of increased carbon edges exposure, abundant accessible active sites, and improved electron/mass transport capability of 3D hierarchically porous architecture. More importantly, when Fe₃Co₇@PCNSs is applied as both cathode and anode in a two-electrode cell for carrying out the overall water splitting process, it just needs the corresponding cell voltages of 1.667 and 1.707 V to attain the 10 and 20 mA cm^-2 current densities respectively. The synthesis of Fe₃Co₇@PCNSs confirms the importance of Fe and Co elements in designing catalyst structures. The electrochemical measurements further display the key roles of structural features and metal alloy@C active sites for boosting water splitting performances.