A Molecular Foaming and Activation Strategy to Porous N-Doped Carbon Foams for Supercapacitors and CO2 Capture

Assembly-foaming synthesis of hierarchically porous nitrogen-doped carbon supported single-atom iron catalysts for efficient oxygen reduction

High-performance electrocatalysts are highly concerned in oxygen reduction reaction (ORR) related energy applications. However, facile synthesis of hierarchically porous structures with highly exposed active sites and improved mass transfer is challenging. Herein, we develop a novel assembly-foaming strategy for synthesizing hierarchically porous nitrogen-doped carbon supported single-atom iron catalysts. Incorporation of a Fe3+/histidine complex into the block copolymer F127/resol assembly system not only enables an assembly-foaming process forming hierarchical pores, but also promotes the creation of abundant nitrogen-coordinated single-atom Fe (FeNX) sites on well-graphitized carbon skeletons. The obtained materials possess interconnected macropores (1.5-11.5 µm), large mesopores (5-30 nm) and rich micropores, high surface areas (534-970 m2 g-1), large pore volumes (0.68-1.04 cm3 g-1) and rich FeNX sites. The optimized sample exhibits a superior ORR activity (onset potential 1.03 V and half-wave potential 0.89 V) to the commercial 20 wt% Pt/C catalyst, a high kinetic current density and excellent stability and methanol tolerance.The prominent performance stems from the coeffects of the hierarchical pore structure and the rich accessible FeNX sites. The significance of the pore structure is revealed by the positive linear relationship between the double-layer capacitances of the obtained materials and their ORR activities.

Encapsulating Sulfur into a Gel-Derived Nitrogen-Doped Mesoporous and Microporous Carbon Sponge for High-Performance Lithium-Sulfur Batteries

The practical application of Li-S batteries (LSBs) has long been impeded by the inefficient utilization of sulfur and slow kinetics. Utilizing conductive carbonaceous frameworks as a host scaffold presents an efficient and cost-effective approach to enhance sulfur utilization for redox reactions in LSBs. However, the interaction of pure carbon materials with lithium polysulfide intermediates (LiPSs) is limited to weak van der Waals forces. Hence, the development of an economical method for synthesizing heteroatom-doped carbon materials for sulfur fixation is of paramount importance. In this study, we introduce a hierarchical porous nitrogen-doped carbon sponge (NPCS) with an exceptionally high BET surface area of 3182.2 m2 g-1, achieved through a facile template-assisted polymerization method. The incorporation of inorganic salts, free radical polymerization, and deuteric freeze-drying techniques facilitates the formation of hierarchical pores within the NPCS. After sulfur fixation, the resulting S/NPCS electrode demonstrates remarkable electrochemical performance in LSBs. Specifically, it achieves an 80% sulfur utilization rate, maintains a high reversible specific capacity of 400 mA h g-1 even after 600 cycles at a demanding current density of 5.0 A g-1, and exhibits superior rate capability. It is believed that this work will inspire the rational design of cost-effective carbon-based electrodes for high-performance LSBs.

Recent Breakthroughs in Supercapacitors Boosted by Macrocycles

Supercapacitors are essential for electrochemical energy storage because of their high-power density, good cycle stability, fast charging and discharging rates, and low maintenance cost. Macrocycles, including cucurbiturils, calixarene, and cyclodextrins, are cage-like organic compounds (with a nanocavity that contains O and N heteroatoms) with unique potential in supercapacitors. Here, we review the applications of macrocycles in supercapacitor systems, and we illustrate the merits of organic macrocycles in electrodes and electrolytes for improving the electrochemical double-layer capacitors and pseudocapacitance via supramolecular strategies. Then, the observed relationships between electrochemical performance and macrocyclic structures are introduced. This comprehensive review describes recent progress on macrocycle-block supercapacitors for researchers.

Modulation of electromagnetic wave absorption via porosity in Pechini-derived carbon guided by a random network model

It is well established that porosity in carbon materials can benefit electromagnetic wave absorption by providing stronger interfacial polarization, better impedance matching, multiple reflections, and lower density, but an in-depth assessment is still lacking on this issue. The random network model describes the dielectric behavior of a conduction-loss absorber-matrix mixture with two parameters related to the volume fraction and conductivity, respectively. In this work, the porosity in carbon materials was tuned by a simple, green, and low-cost Pechini method, and the mechanism of how porosity affects EM wave absorption was investigated quantitatively based on the model. It was discovered that porosity was crucial for the formation of a random network, and a higher specific pore volume led to a larger volume fraction parameter and a lower conductivity parameter. Guided by the high throughput parameter sweeping based on the model, the Pechini-derived porous carbon could achieve an effective absorption bandwidth of 6.2 GHz at 2.2 mm. This study further verifies the random network model, unveiling the implication and influencing factors of the parameters, and opens a new path to optimize the electromagnetic wave absorption performance of conduction-loss materials.

Engineering HOF-Based Mixed-Matrix Membranes for Efficient CO2 Separation

Hydrogen-bonded organic frameworks (HOFs) have emerged as a new class of crystalline porous materials, and their application in membrane technology needs to be explored. Herein, for the first time, we demonstrated the utilization of HOF-based mixed-matrix membrane for CO2 separation. HOF-21, a unique metallo-hydrogen-bonded organic framework material, was designed and processed into nanofillers via amine modulator, uniformly dispersing with Pebax polymer. Featured with the mix-bonded framework, HOF-21 possessed moderate pore size of 0.35 nm and displayed excellent stability under humid feed gas. The chemical functions of multiple binding sites and continuous hydrogen-bonded network jointly facilitated the mass transport of CO2. The resulting HOF-21 mixed-matrix membrane exhibited a permeability above 750 Barrer, a selectivity of ~ 40 for CO2/CH4 and ~ 60 for CO2/N2, surpassing the 2008 Robeson upper bound. This work enlarges the family of mixed-matrix membranes and lays the foundation for HOF membrane development.

Progress in the use of organic potassium salts for the synthesis of porous carbon nanomaterials: microstructure engineering for advanced supercapacitors

Porous carbon nanomaterials (PCNs) are widely applied in energy storage devices. Traditionally, PCNs were mainly synthesized by activation and templating methods, which are time-consuming, tedious, corrosive and relatively high cost. Therefore, the development of easier and greener methods to produce PCNs is of great significance. Recently, organic potassium salts (OPSs) emerged as versatile reagents for synthesizing PCNs. The OPS-based synthesis of PCNs can avoid the use of large amounts of corrosive chemical agents. Potassium carbonate generated in situ from the decomposition of OPSs could serve as both a green activation agent and a water-removable template to produce nanopores. Potassium oxide and potassium formed at higher temperature could generate additional porosity, contributing to a highly porous architecture. The carbon-rich organic moiety could function as a carbon precursor and chemical blowing agent. This review aims to elucidate the multifunctionality of OPSs in the synthesis of PCNs and the capacitive performance of the corresponding PCNs. To this end, recent progress on the capacitive performance of PCNs synthesized from OPSs is summarized. This review provides constructive viewpoints for the cost-effective and green synthesis of PCNs with the aid of OPSs for application in supercapacitors.

Regulating the Electron Localization of Metallic Bismuth for Boosting CO2 Electroreduction

Electrochemical reduction of CO2 to formate is economically attractive but improving the reaction selectivity and activity remains challenging. Herein, we introduce boron (B) atoms to modify the local electronic structure of bismuth with positive valence sites for boosting conversion of CO2 into formate with high activity and selectivity in a wide potential window. By combining experimental and computational investigations, our study indicates that B dopant differentiates the proton participations of rate-determining steps in CO2 reduction and in the competing hydrogen evolution. By comparing the experimental observations with the density functional theory, the dominant mechanistic pathway of B promoted formate generation and the B concentration modulated effects on the catalytic property of Bi are unravelled. This comprehensive study offers deep mechanistic insights into the reaction pathway at an atomic and molecular level and provides an effective strategy for the rational design of highly active and selective electrocatalysts for efficient CO2 conversion.

Constructing highly porous carbon materials from porous organic polymers for superior CO2 adsorption and separation

The increase in atmospheric carbon dioxide (CO₂) concentration has led to numerous problems related to our living environment, seeking an efficient carbon capture and storage (CCS) strategy associated with low energy consumption and expenditures is highly desirable. Here, we demonstrate a facile approach to synthesize a series of highly porous carbon materials derived from porous organic polymers synthesized from three low-cost isomers of triphenyl using chemical activation with KOH at different temperatures. Compared with the precursor porous organic polymers, the porosity of the prepared porous carbon materials is significantly enhanced with surface areas as high as 3367 m² g^-1 and pore volumes up to 1.224 cm³ g^-1. Notably, such porous carbon materials deliver an exceptionally high CO₂ adsorption capacity of 7.78 mmol g^-1 at 273 K and 1 bar, a value that is superior to most of the previously reported adsorbents. In addition, these porous organic polymers and derived porous carbon materials exhibit high CO₂/N₂ selectivity at ambient conditions. Therefore, the facile construction of highly porous carbon materials from porous organic polymers may offer an efficient strategy for CO₂ adsorption and separation and further mitigates greenhouse effect.

Recent Advances in Interface Engineering for Electrocatalytic CO2 Reduction Reaction

Electrocatalytic CO₂ reduction reaction (CO₂RR) can store and transform the intermittent renewable energy in the form of chemical energy for industrial production of chemicals and fuels, which can dramatically reduce CO₂ emission and contribute to carbon-neutral cycle. Efficient electrocatalytic reduction of chemically inert CO₂ is challenging from thermodynamic and kinetic points of view. Therefore, low-cost, highly efficient, and readily available electrocatalysts have been the focus for promoting the conversion of CO₂. Very recently, interface engineering has been considered as a highly effective strategy to modulate the electrocatalytic performance through electronic and/or structural modulation, regulations of electron/proton/mass/intermediates, and the control of local reactant concentration, thereby achieving desirable reaction pathway, inhibiting competing hydrogen generation, breaking binding-energy scaling relations of intermediates, and promoting CO₂ mass transfer. In this review, we aim to provide a comprehensive overview of current developments in interface engineering for CO₂RR from both a theoretical and experimental standpoint, involving interfaces between metal and metal, metal and metal oxide, metal and nonmetal, metal oxide and metal oxide, organic molecules and inorganic materials, electrode and electrolyte, molecular catalysts and electrode, etc. Finally, the opportunities and challenges of interface engineering for CO₂RR are proposed.

Sustainable Carbon Materials toward Emerging Applications

It is desirable for a sustainable society that the production and utilization of renewable materials are net-zero in terms of carbon emissions. Carbon materials with emerging applications in CO₂ utilization, renewable energy storage and conversion, and biomedicine have attracted much attention both academically and industrially. However, the preparation process of some new carbon materials suffers from energy consumption and environmental pollution issues. Therefore, the development of low-cost, scalable, industrially and economically attractive, sustainable carbon material preparation methods are required. In this regard, the use of biomass and its derivatives as a precursor of carbon materials is a major feature of sustainability. Recent advances in the synthetic strategy of sustainable carbon materials and their emerging applications are summarized in this short review. Emphasis is made on the discussion of the original intentions and various sustainable strategies for producing sustainable carbon materials. This review provides basic insights and significant guidelines for the further design of sustainable carbon materials and their emerging applications in catalysis and the biomedical field.

Oxidized-Polydopamine-Coated Graphene Anodes and N,P Codoped Porous Foam Structure Activated Carbon Cathodes for High-Energy-Density Lithium-Ion Capacitors

As a tradeoff between supercapacitors and batteries, lithium-ion capacitors (LICs) are designed to deliver high energy density, high power density, and long cycling stability. Owing to the different energy storage mechanisms of capacitor-type cathodes and battery-type anodes, engineering and fabricating LICs with excellent energy density and power density remains a challenge. Herein, to alleviate the mismatch between the anode and cathode, we ingeniously designed a graphene with oxidized-polydopamine coating (LG@DA1) and N,P codoped porous foam structure activated carbon (CPC750) as the battery-type anode and capacitor-type cathode, respectively. Using oxidized-polydopamine to stabilize the structure of graphene, increase layer spacing, and modify the surface chemical property, the LG@DA1 anode delivers a maximum capacity of 1100 mAh g^-1 as well as good cycling stability. With N,P codoping and a porous foam structure, the CPC750 cathode exhibits a large effective specific surface area and a high specific capacity of 87.5 mAh g^-1. In specific, the present LG@DA1//CPC750 LIC showcases a high energy density of 170.6 Wh kg^-1 and superior capacity retention of 93.5% after 2000 cycles. The success of the present LIC can be attributed to the structural stability design, surface chemistry regulation, and enhanced utilization of effective active sites of the anode and cathode; thus, this strategy can be applied to improve the performance of LICs.

More Sustainable Chemical Activation Strategies for the Production of Porous Carbons

The preparation of porous carbons attracts a great deal of attention given the importance of these materials in many emerging applications, such as hydrogen storage, CO₂ capture, and energy storage in supercapacitors and batteries. In particular, porous carbons produced by applying chemical activation methods are preferred because of the high pore development achieved. However, given the environmental risks associated with conventional activating agents such as KOH, the development of greener chemical activation methodologies is an important objective. This Review summarizes recent progress in the production of porous carbons by using more sustainable strategies based on chemical activation. The use of less-corrosive chemical agents as an alternative to KOH is thoroughly reviewed. In addition, progress achieved to date by using emerging self-activation methodologies applied to organic salts and biomass products is also discussed.