Ultrafast Porous Carbon Activation Promises High-Energy Density Supercapacitors

Acid-modified biomass-based N-doped O-rich hierarchical porous carbon as a high-performance electrode for supercapacitors

In contemporary society, the conversion and efficient utilization of waste biomass and its derivatives are of great significance. Carbonized wood (CW) is an easily accessible and cost-effective green resource, but it has limitations as an electrode material due to its low specific surface area, limited active sites and poor conductivity. Therefore, it is crucial to improve the performance of biomass-based materials by using activation, heteroatom doping and modification methods to enhance the specific surface area and active sites. In this study, we developed acid-modified urea-doped activated carbonized wood (AUACW) with a three-dimensional (3D) porous structure and porosity, achieving a high specific surface area of 1321.3 m2 g-1. In addition, the degree of graphitization (ID/IG = 1.0) provides good conductivity and a large number of active sites, which are conducive to charge transfer and ion diffusion. The increase of nitrogen and oxygen elements enhances the surface wettability of the material and provides additional pseudocapacitance. The specific capacitance of AUACW reaches 435.84 F g-1 at 0.8 A g-1 with a 93.6% capacitance retention after 10 000 cycles in a 1 M KOH electrolyte. More attractively, a symmetrical supercapacitor (SSC) based on AUACW delivers an energy density of 22.61 W h kg-1 at a power density of 533.26 W kg-1. This work demonstrates the promising potential of utilizing waste biomass to develop green and valuable carbon materials for supercapacitors.

Advancements in Manganese-Based Cathode for Sustainable Energy Utilization

Manganese-based compounds, especially manganese oxides, are one of the most exceptional electrode materials. Specifically, manganese oxides have gained significant interest owing to their unique crystal structures, high theoretical capacity, abundant natural availability and eco-friendly nature. However, as transition metal semiconductors, manganese oxide possess low electrical conductivity, limited rate capacity, and suboptical cycle stability. Thus, combining manganese oxides with carbon or other metallic materials can significantly improve their electrochemical performance. These composites increase active sites and conductivity, thereby improving electrode reaction kinetics, cycle stability, and lifespan of supercapacitors (SCs) and batteries. This paper reviews the latest applications of Mn-based cathodes in SCs and advanced batteries. Moreover, the energy storage mechanisms were also proposed. In this review, the development prospects and challenges for advanced energy storage applications of Mn-based cathodes are summarized.

Precise Tuning of Hollow and Pore Size of Bimetallic MOFs Derivate to Construct High-Performance Nanoscale Materials for Supercapacitors and Sodium-Ion Batteries

Precise control of pore volume and size of carbon nanoscale materials is crucial for achieving high capacity and rate performances of charge/discharge. In this paper, starting from the unique mechanism of the role of In, Zn combination, and carboxyl functional groups in the formation of the lumen and pore size, the composition of InZn-MIL-68 is regulated to precisely tune the diameter and wall pore size of the hollow carbon tubes. The hollow carbon nanotubes (CNT) with high-capacity storage and fast exchange of Na+ ions and charges are prepared. The CNT possess ultra-high specific capacitance and ultra-long cycle life and also offer several times higher Na+ ion storage capacity and rate performance than the existing CNTs. Density functional theory calculations and tests reveal that these superior characteristics are attributed to the spacious hollow structure, which provides sufficient space for Na+ storage and the tube wall's distinctive porosity of tube wall as well as open ends for facilitating Na+ rapid desorption. It is believed that precise control of sub-nanopore volume and pore size by tuning the composition of the carbon materials derived from bimetallic metal-organic frameworks (MOFs) will establish the basis for the future development of high-energy density and high-power density supercapacitors and batteries.

Study of Zinc Diffusion Based on S, N-Codoped Honeycomb Carbon Cathodes for High-Performance Zinc-Ion Capacitors

Capacitors with zinc ions, with excellent stabilities, low cost, and high energy density, are expected to be promising energy storage devices. However, the development of zinc-ion capacitors is quietly restricted by low specific capacity and cycling stability. Herein, to overcome these limitations, honeycomb-structured S, N-codoped carbon (SNPC) is constructed by one-pot calcination of waste corn bracts and thiourea. The honeycomb structure of SNPC is demonstrated to provide abundant active sites that can enhance the extron/ion transport, conductivity for high power export, and ion adsorption capacity in energy storage applications, leading to a higher electrochemical performance achieved. The electrolytes of zinc salt have also been studied. It reveals that the SNPC electrode presents the best electrochemical performance in a 2 M ZnSO4 and 0.5 M ZnCl2 electrolyte mixture because in the electrolyte mixture, Cl- can replace the existing bound water in the solvation structure to form an anion-type water-free solvation structure ZnCl42-. The SNPC-800 electrode with a highly improved surface area (∼909.0 m2 g-1) is proved to be more suitable as the electrode than other materials. Aqueous zinc-ion capacitors (ZICs) have been assembled by the honeycomb-structured SNPC-800 as the cathode, which can achieve a relatively wide working voltage range of 0.1-1.8 V. The SNPC-800 ZICs exhibit a superior specific capacity of 179.1 mA h g-1 at 0.1 A g-1. The energy density of SNPC-800 ZICs reaches an impressive value of 89.6 Wh kg-1 at 53.8 W kg-1, and it sustains 28.3 Wh kg-1 at 1997.6 W kg-1. In addition, there is 99.8% capacity retention in the SNPC-800 ZICs over 5000 cycles. The absorption energy in SPNC is much higher than that in undoped CPC, as confirmed by density functional theory, which reveals that introducing of heteroatoms (S, N) has a comparatively active advantage at increasing the Zn-ion storage capacity. This work proposes a practical strategy for the effective recycling of waste biomass materials into honeycomb carbon electrode materials. Moreover, the honeycomb carbon-based ZICs with excellent electrochemical performance and long-term cycling stability possess great potential to be a superior cathode in practical applications.

Bimetallic-MOF Derived Carbon with Single Pt Anchored C4 Atomic Group Constructing Super Fuel Cell with Ultrahigh Power Density And Self-Change Ability

Pursuing high power density with low platinum catalysts loading is a huge challenge for developing high-performance fuel cells (FCs). Herein, a new super fuel cell (SFC) is proposed with ultrahigh output power via specific electric double-layer capacitance (EDLC) + oxygen reduction reaction (ORR) parallel discharge, which is achieved using the newly prepared catalyst, single-atomic platinum on bimetallic metal-organic framework (MOF)-derived hollow porous carbon nanorods (PtSA /HPCNR). The PtSA-1.74 /HPCNR-based SFC has a 3.4-time higher transient specific power density and 13.3-time longer discharge time with unique in situ self-charge and energy storage ability than 20% Pt/C-based FCs. X-ray absorption fine structure, aberration-corrected high-angle annular dark-field scanning transmission electron microscope, and density functional theory calculations demonstrate that the synergistic effect of Pt single-atoms anchored on carbon defects significantly boosts its electron transfer, ORR catalytic activity, durability, and rate performance, realizing rapid " ORR+EDLC" parallel discharge mechanism to overcome the sluggish ORR process of traditional FCs. The promising SFC leads to a new pathway to boost the power density of FCs with extra-low Pt loading.

Poly (Ionic Liquid)-Metal Organic Framework-Derived Nanoporous Carbon Membranes: Facile Fabrication and Ultrahigh Areal Capacitance

With the rapid development of energy storage technology, the operation of portable and wearable devices is inseparable from high energy density power supplies. However, the demand for high performance supercapacitors in movable smart electronics is still restrained by their insufficient areal capacitance and limited power/energy densities. In addition, some electroactive materials, including metal oxides, conductive polymers, graphene, porous carbons, etc., are inevitable to use extra adhesives for the preparation of electrode materials. In this work, integrated hierarchical graphitic porous carbon membranes used as the electrodes without adhesives are successfully synthesized, via pyrolyzing poly(ionic liquid)s (PILs)-metal organic frameworks (MOFs) composite membranes. The asymmetric supercapacitor is assembled by the carbonized PIL-MOF composite membrane and PILs-derived porous carbon membrane, and exhibits significant areal capacitance with remarkable power and energy densities. In the two-electrode system, the areal capacitance can reach 9.5 F cm-2 with an energy density of 1.91 mWh cm-2 . In the fabricated all-solid-state supercapacitors, the areal capacitance and energy density achieved 3.2 F cm-2 and 0.65 mWh cm-2 , respectively, exceeding most reported ones. Therefore, the integrated carbon membrane electrodes with high areal capacitance reveal great potential in miniaturized devices, and further show a wider application scope through regulating PILs.

Recent Advances in Porous Carbon Materials as Electrodes for Supercapacitors

Porous carbon materials have demonstrated exceptional performance in various energy and environment-related applications. Recently, research on supercapacitors has been steadily increasing, and porous carbon materials have emerged as the most significant electrode material for supercapacitors. Nonetheless, the high cost and potential for environmental pollution associated with the preparation process of porous carbon materials remain significant issues. This paper presents an overview of common methods for preparing porous carbon materials, including the carbon-activation method, hard-templating method, soft-templating method, sacrificial-templating method, and self-templating method. Additionally, we also review several emerging methods for the preparation of porous carbon materials, such as copolymer pyrolysis, carbohydrate self-activation, and laser scribing. We then categorise porous carbons based on their pore sizes and the presence or absence of heteroatom doping. Finally, we provide an overview of recent applications of porous carbon materials as electrodes for supercapacitors.

Rational design of dense microporous carbon derived from coal tar pitch towards high mass loading supercapacitors

The compact carbon materials with huge specific surface area (SSA) and proper pore structure are highly desirable towards high-performance supercapacitors at the cell level. However, to well balance of porosity and density is still an on-going task. Herein, a universal and facile strategy of pre-oxidation-carbonization-activation is employed to prepare the dense microporous carbons from coal tar pitch. The optimized sample POCA800 not only possesses a well-developed porous structure with the SSA of 2142 m² g^-1 and total pore volume (V_t) of 1.540 cm³ g^-1, but also exhibits a high packing density of 0.58 g cm^-3 and proper graphitization. Owing to these advantages, POCA800 electrode at areal mass loading of 10 mg cm^-2 shows a high specific capacitance of 300.8 F g^-1 (174.5 F cm^-3) at 0.5 A g^-1 and good rate performance. The POCA800 based symmetrical supercapacitor with a total mass loading of 20 mg cm^-2 displays a large energy density of 8.07 Wh kg^-1 at 125 W kg^-1 and remarkable cycling durability. It is revealed that the prepared density microporous carbons are promising for practical applications.

Superfast Mass Transport of Na/K Via Mesochannels for Dendrite-Free Metal Batteries

Fast ion diffusion in anode hosts enabling uniform distribution of Li/Na/K is essential for achieving dendrite-free alkali-metal batteries. Common strategies, e.g. expanding the interlayer spacing of anode materials, can enhance bulk diffusion of Li but are less efficient for Na and K due to their larger ionic radius. Herein, a universal strategy to drastically improve the mass-transport efficiency of Na/K by introducing open mesochannels in carbon hosts is proposed. Such pore engineering can increase the accessible surface area by one order of magnitude, thus remarkably accelerating surface diffusion, as visualized by in situ transmission electron microscopy. In particular, once the mesochannels are filled by the Na/K metals, they become the superfast channels for mass transport via the mechanism of interfacial diffusion. Thus-modified carbon hosts enable Na/K filling in their inner cavities and uniform deposition across the whole electrodes with fast kinetics. The resulting Na-metal anodes can exhibit stable dendrite-free cycling with outstanding rate performance at a high current density of up to 30 mA cm^-2 . This work presents an inspiring attempt to address the sluggish transport issue of Na/K, as well as valuable insights into the mass-transport mechanism in porous anodes for high-performance alkali-metal storage.

Dual-Silica Template-Mediated Synthesis of Nitrogen-Doped Mesoporous Carbon Nanotubes for Supercapacitor Applications

1D carbon nanotubes have been widely applied in many fields, such as catalysis, sensing and energy storage. However, the long tunnel-like pores and relatively low specific surface area of carbon nanotubes often restrict their performance in certain applications. Herein, a dual-silica template-mediated method to prepare nitrogen-doped mesoporous carbon nanotubes (NMCTs) through co-depositing polydopamine (both carbon and nitrogen precursors) and silica nanoparticles (the porogen for mesopore formation) on a silica nanowire template is proposed. The obtained NMCTs have a hierarchical pore structure of large open mesopores and tubular macropores, a high specific surface area (1037 m² g^-1 ), and homogeneous nitrogen doping. The NMCT-45 (prepared at an interval time of 45 min) shows excellent performance in supercapacitor applications with a high capacitance (373.6 F g^-1 at 1.0 A g-¹ ), excellent rate capability, high energy density (11.6 W h kg^-1 at a power density of 313 W kg^-1 ), and outstanding cycling stability (98.2% capacity retention after 10 000 cycles at 10 A g^-1 ). Owing to the unique tubular morphology, hierarchical porosity and homogeneous N-doping, the NMCT also has tremendous potential in electrochemical catalysis and sensing applications.

Highly Porous Carbon Aerogels for High-Performance Supercapacitor Electrodes

In recent years, porous carbon materials with high specific surface area and porosity have been developed to meet the commercial demands of supercapacitor applications. Carbon aerogels (CAs) with three-dimensional porous networks are promising materials for electrochemical energy storage applications. Physical activation using gaseous reagents provides controllable and eco-friendly processes due to homogeneous gas phase reaction and removal of unnecessary residue, whereas chemical activation produced wastes. In this work, we have prepared porous CAs activated by gaseous carbon dioxide, with efficient collisions between the carbon surface and the activating agent. Prepared CAs display botryoidal shapes resulting from aggregation of spherical carbon particles, whereas activated CAs (ACAs) display hollow space and irregular particles from activation reactions. ACAs have high specific surface areas (2503 m² g^-1) and large total pore volumes (1.604 cm³ g^-1), which are key factors for achieving a high electrical double-layer capacitance. The present ACAs achieved a specific gravimetric capacitance of up to 89.1 F g^-1 at a current density of 1 A g^-1, along with a high capacitance retention of 93.2% after 3000 cycles.

Reconfiguring the Electronic Structure of Heteroatom Doped Carbon Supported Bimetallic Oxide@Metal Sulfide Core-Shell Heterostructure via In Situ Nb Incorporation toward Extrinsic Pseudocapacitor

High-energy-density battery-type materials have sparked considerable interest as supercapacitors electrode; however, their sluggish charge kinetics limits utilization of redox-active sites, resulting in poor electrochemical performance. Here, the unique core-shell architecture of metal organic framework derived N-S codoped carbon@Co_x S_y micropetals decorated with Nb-incorporated cobalt molybdate nanosheets (Nb-CMO₄ @C_x S_y NC) is demonstrated. Coordination bonding across interfaces and π-π stacking interactions between CMO₄ @C_x S_y and N and, S-C can prevent volume expansion during cycling. Density functional theory analysis reveals that the excellent interlayer and the interparticle conductivity imparted by Nb doping in heteroatoms synergistically alter the electronic states and offer more accessible species, leading to increased electrical conductivity with lower band gaps. Consequently, the optimized electrode has a high specific capacity of 276.3 mAh g^-1 at 1 A g^-1 and retains 98.7% of its capacity after 10 000 charge-discharge cycles. A flexible quasi-solid-state SC with a layer-by-layer deposited reduced graphene oxide /Ti₃ C₂ T_X anode achieves a specific energy of 75.5 Wh kg^-1 (volumetric energy of 1.58 mWh cm^-3 ) at a specific power of 1.875 kWh kg^-1 with 96.2% capacity retention over 10 000 charge-discharge cycles.

Ultrafast Non-Equilibrium Synthesis of Cathode Materials for Li-Ion Batteries

The synthesis of cathode materials plays an important role in determining the production efficiency, cost, and performance of lithium-ion batteries. However, conventional synthesis methods always experience a slow heating rate and involve a complicated multistep reaction process and sluggish reaction dynamics, leading to high energy and long time consumption. Herein, a high-temperature shock (HTS) strategy is reported for the ultrafast synthesis of cathode materials in seconds. The HTS process experiences an ultrahigh heating rate, leading to a non-equilibrium reaction and fast reaction kinetics, and avoids high energy and long time consumption. Mainstream cathode materials (such as LiMn₂ O₄ , LiCoO₂ , LiFePO₄ , and Li-rich layered oxide/NiO heterostructured material) are successfully synthesized with pure phases, oxygen vacancies, ultrasmall particle sizes, and good electrochemical performance. The HTS process not only provides an efficient synthesis approach for cathode materials, but also can be extended beyond lithium-ion batteries.

Mango-Stone-Derived Nitrogen-Doped Porous Carbon for Supercapacitors

The preparation of N-doped porous carbon (NC-800) is presented via facile mango stone carbonization at 800 °C. The NC-800 material exhibits good cycle stability (the capacity retention is 97.8% after 5000 cycles) and high specific capacitance of 280 F/g at 1 A/g. Furthermore, the assembled symmetric device of NC-800//NCs-800 exhibits about 31.1 Wh/kg of energy density at 800 W/kg in a voltage range of 0-1.6 V. The results of the study suggest that NC-800 may be a promising energy storage material for practical application.