Unraveling the Capacitive Charge Storage Mechanism of Nitrogen-Doped Porous Carbons by EQCM and ssNMR

Spatially synthesized fluorine-modified graphene improves double times higher capacitance than theoretical capacitance of graphene in alkaline medium

The practically low energy density limits the large-scale application of graphene in supercapacitors. Here, we propose a space-confined method for the preparation of fluorine-modified graphene (FG) by using fluorine-containing groups (PF6- or BF4-) as co-intercalated ions and reactants. The semi-ionic C-F bonds in FG contribute a brilliant capacitive performance in both acidic and alkaline electrolytes. Particularly, in alkaline medium, the FG electrode exhibited an ultrahigh specific capacitance (1210 F g-1), surpassing 2 orders of the theoretical capacitance value of graphene. Meanwhile, the FG-assembled symmetrical supercapacitor device (FG-SSD) possesses ultrahigh energy density (418.7 Wh kg-1) and power density (2 kW kg-1) in acidic medium, highlighting the practical application of supercapacitors. Theoretical calculations revealed an increased electrochemical double layer capacitance and amplified the electrochemical window of FG-SSD. This work demonstrates a spatially confined method for the preparation of functional graphene and its spectacular potential for supercapacitor-related electronics.

π-Conjugated Microporous Hydrocarbon Electrodes for High-Capacity and High-Voltage Lithium-Ion Capacitors

Carbon-based cathodes are widely utilized in lithium-ion capacitors due to their superior cycle stability, safety, and tolerance to overcharging compared to oxide-based cathodes. However, the limited capacity of carbon cathodes, primarily governed by the electric double-layer capacitance mechanism, constrains their energy storage potential. Conventional strategies like increasing surface area and pore volume have provided marginal improvements, while heteroatom doping has been restricted by low working voltage and compromised conductivity. To overcome these limitations, a novel class of π-conjugated microporous hydrocarbons (CMHs) is developed using sub-graphitic polycyclic aromatic hydrocarbons (PAH) as building blocks. These materials PPe, PPy, and PAn feature carbon-like large π-conjugated surfaces, abundant oxygen-free edge C(sp2)-H sites, and well-defined microporous structures, facilitating anion adsorption and ion transport. Among them, PPe demonstrates exceptional performance with a high voltage of 3.13 V vs Li+/Li, a remarkable capacity of 241 mAh g-1 2.5 times of commercial activated carbon (YP50), and exceptional rate performance (up to 50 A g-1), far surpassing all other reported LIC cathode materials. These findings provide a fundamental design strategy for carbon-based cathodes in LICs that highlighting the role of π-conjugation and edge chemistry in electrochemical performance, paving the way for next-generation high-capacity, high-voltage energy storage devices.

Elucidating Relay Catalysis on Copper Clusters With Satellite Single Atoms for Enhanced Urea Electrosynthesis

Relay catalysis represents significant efficacy in alleviating competition among different reactants during coupling reactions. However, a comprehensive understanding of the reaction mechanism underlying relay catalysis for the urea electrosynthesis remains challenging. Herein, we have developed a catalyst (CuAC-CuSA@NC) comprising Cu atomic clusters (CuAC) with satellite Cu─N4 single atoms (CuSA) sites on the nitrogen-doped porous interconnected carbon skeleton (NC), enabling elucidation of a relay catalysis process for co-reduction of CO2 and NO3 -. The designed CuAC-CuSA@NC catalyst exhibits an approximately threefold higher urea yield rate compared to that of CuSA@NC at -1.3 V versus RHE. Ex-situ experimental results and in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy analysis reveal a formation sequence between the *NH2 and *NH2CO species on CuAC-CuSA@NC with increasing reduction potential. The combination of theoretical calculations further elucidates that the relay catalysis pathway involves "CuAC" sites facilitating the conversion of *NO3 to *NOx, followed by a hydrogenation process to form *NH2 with *H from water dissociation promoted by "CuSA" sites, which subsequently couples with *CO2 to produce urea. This work provides novel insights into the investigation of coupling reactions, but not limit to, urea synthesis.

Redefining closed pores in carbons by solvation structures for enhanced sodium storage

Closed pores are widely accepted as the critical structure for hard carbon negative electrodes in sodium-ion batteries. However, the lack of a clear definition and design principle of closed pores leads to the undesirable electrochemical performance of hard carbon negative electrodes. Herein, we reveal how the evolution of pore mouth sizes determines the solvation structure and thereby redefine the closed pores. The precise and uniform control of the pore mouth sizes is achieved by using carbon molecular sieves as a model material. We show when the pore mouth is inaccessible to N2 but accessible to CO2 molecular probes, only a portion of solvent shells is removed before entering the pores and contact ion pairs dominate inside pores. When the pore mouth is inaccessible to CO2 molecular probes, namely smaller than 0.35 nm, solvent shells are mostly sieved and dominated anion aggregates produce a thin and inorganic NaF-rich solid electrolyte interphase inside pores. Closed pores are accordingly redefined, and initial coulombic efficiency, cycling and low-temperature performance are largely improved. Furthermore, we show that intrinsic defects inside the redefined closed pores are effectively shielded from the interfacial passivation and contribute to the increased low-potential plateau capacity.

Enhanced electro-catalysis for methanol oxidation reaction performance by edge defects of ordered mesoporous carbon

Heteroatom-doped carbon materials are widely used to improve the electrocatalytic oxidation of methanol; however, the underlying mechanisms driving this enhancement remain poorly understood. A major challenge lies in developing non-doped carbon supports with tunable intrinsic defect types tailored for metal-based catalysts. In this study, we synthesize a series of ordered mesoporous carbon (OMC) supports with adjustable edge defect densities by varying roasting temperatures and employing a zinc (Zn) evaporation strategy to systematically investigate the impact of edge defects on methanol oxidation reaction (MOR) performance. Theoretical calculations and structural characterizations confirm that the electron metal-support interaction (EMSI) between OMC edge defects and palladium nanoparticles (Pd NPs) effectively modulates the electronic structure of Pd NPs. This modulation not only enhances overall reaction activity and selectivity for the non-CO pathway but also strengthens the anchoring of Pd NPs, leading to superior activity and stability of the Pd/OMC-Zn0.55 catalyst in methanol electrocatalytic oxidation. Notably, after rigorously excluding the influence of various physicochemical properties of the carbon supports, the crucial role of edge defects in improving MOR performance is established. This work provides essential insights into the controlled synthesis of carbon-based catalysts with edge defects and introduces promising strategies for the development of high-performance anode catalysts for direct methanol fuel cells.

Hierarchical Carbon-Based Electrocatalyst with Functional Separation Properties for Efficient pH Universal Nitrate Reduction

The electrocatalytic reduction of nitrate (eNO3 -RR) to ammonia (NH3) across varying pH is of great significance for the treatment of practical wastewater containing nitrate. However, developing highly active and stable catalysts that function effectively in a wide pH range remains a formidable challenge. Herein, a hierarchical carbon-based metal-free electrocatalyst (C-MFEC) of winged carbon coaxial nanocables (W-CCNs, in situ generated graphene nanosheets and outside carbon layer with abundant topological defects from pristine carbon nanotubes, CNTs), is prepared through moderate oxidation of CNTs and the subsequent introduction of topological defects. The W-CCNs feature functional separation properties, with an inner core of pristine CNTs that facilitates efficient charge transfer, while the outer shell is composed of in situ generated graphene nanosheets and carbon layers enriched with topological defects characterized by distinct carbon atom configurations, which play a crucial role in promoting the adsorption of NO3 -, the dissociation of water, and the N─H bond formation. This innovative design enables the C-MFEC to exhibit outstanding performance for eNO3 -RR, operating efficiently with the NH3 yield rates of 49.5, 75.3, and 88.1 g h-1 gcat. -1 in acidic, neutral, and alkaline media, respectively. Such performance metrics not only outshine C-MFECs but also rival or surpass those of certain metal-based catalysts.

Unveiling the neglected role of oxygen doping in nitrogen-doped carbon for enhanced capacitive deionization performance

Nitrogen-doped carbons (NCs) have demonstrated notable advantages for application in capacitive deionization (CDI). However, the potential roles of different nitrogen configurations in the CDI process, especially how the neglected oxygen doping synergistically works, remain unclear. In this work, we systematically addressed these critical issues and revealed the significant role of trace oxygen doping in enhancing the desalination performance of NC electrodes. By introducing oxygen into nitrogen-doped carbon nanosheets (ONC-S), using guanine as the precursor, we obtained abundant pyridinic and pyrrolic nitrogen configurations. This design aims to synergistically enhance the charge distribution, wettability, and ion diffusion of the target electrodes. Compared with commercial activated carbon and other state-of-the-art materials, our ONC-S electrode demonstrates superior specific capacitance, excellent cycling stability, and enhanced desalination efficiency. These findings highlight the synergistic effects of trace oxygen doping and the nitrogen configuration, offering valuable insights into the mechanisms driving the improved CDI performance.

Accelerating Ion Desolvation via Bioinspired Ion Channel Design in Nonconcentrated Aqueous Electrolytes

In aqueous-based electrochemical energy storage devices, uncontrolled hydrolysis of water at the electrochemical interfaces limits the application of such aqueous batteries or supercapacitors in business. The "water-in-salt" design is a valid strategy to broaden the electrochemical stability window in aqueous electrolytes, but drawbacks such as high manufacturing cost, high electrolyte viscosity, etc., also hinder its development. Here, inspired by biological ion channels in cell membranes, we propose an effective approach to engineer the electrode surface, inducing the desolvation of hydrated ions at the electrochemical interface and inhibiting water decomposition in nonconcentrated electrolytes. The biological engineering strategy enables the induction of controlled desolvation and accelerates the transportation of hydrated ions, e.g., potassium. The subnanometer design (0.8 nm) forces the hydrated potassium ions to shed their solvation shell with a hydration number of only 0.3, while the electrostatic interactions between the pore groups and the potassium ions facilitate their transport. The Zn||Zn cells demonstrate a stable cycling lifespan of over 1000 h at 1 mA cm-2/10 mAh cm-2. This work sheds new light on regulating the electrochemical interfaces in low-concentration aqueous electrolytes for designing aqueous-based energy storage devices.

Advanced characterization of confined electrochemical interfaces in electrochemical capacitors

The advancement of high-performance fast-charging materials has significantly propelled progress in electrochemical capacitors (ECs). Electrochemical capacitors store charges at the nanoscale electrode material-electrolyte interface, where the charge storage and transport mechanisms are mediated by factors such as nanoconfinement, local electrode structure, surface properties and non-electrostatic ion-electrode interactions. This Review offers a comprehensive exploration of probing the confined electrochemical interface using advanced characterization techniques. Unlike classical two-dimensional (2D) planar interfaces, partial desolvation and image charges play crucial roles in effective charge storage under nanoconfinement in porous materials. This Review also highlights the potential of zero charge as a key design principle driving nanoscale ion fluxes and carbon-electrolyte interactions in materials such as 2D and three-dimensional (3D) porous carbons. These considerations are crucial for developing efficient and rapid energy storage solutions for a wide range of applications.

Fundamental Insights into the Direct Electron Transfer Mechanism on Ag Atomic Cluster

The nonradical oxidation pathway for pollutant degradation in Fenton-like catalysis is favorable for water treatment due to the high reaction rate and superior environmental robustness. However, precise regulation of such reactions is still restricted by our poor knowledge of underlying mechanisms, especially the correlation between metal site conformation of metal atom clusters and pollutant degradation behaviors. Herein, we investigated the electron transfer and pollutant oxidation mechanisms of atomic-level exposed Ag atom clusters (AgAC) loaded on specifically crafted nitrogen-doped porous carbon (NPC). The AgAC triggered a direct electron transfer (DET) between the terminal oxygen (Oα) of surface-activated peroxodisulfate and the electron-donating substituents-containing contaminants (EDTO-DET), rendering it 11-38 times higher degradation rate than the reported carbon-supported metal catalysts system with various single-atom active centers. Heterocyclic substituents and electron-donating groups were more conducive to degradation via the EDTO-DET system, while contaminants with high electron-absorbing capacity preferred the radical pathway. Notably, the system achieved 79.5% chemical oxygen demand (COD) removal for the treatment of actual pharmaceutical wastewater containing 1053 mg/L COD within 30 min. Our study provides valuable new insights into the Fenton-like reactions of metal atom cluster catalysts and lays an important basis for revolutionizing advanced oxidation water purification technologies.

Electrostatically Designing Materials and Interfaces

Collective electrostatic effects arise from the superposition of electrostatic potentials of periodically arranged (di)polar entities and are known to crucially impact the electronic structures of hybrid interfaces. Here, it is discussed, how they can be used outside the beaten paths of materials design for realizing systems with advanced and sometimes unprecedented properties. The versatility of the approach is demonstrated by applying electrostatic design not only to metal-organic interfaces and adsorbed (complex) monolayers, but also to inter-layer interfaces in van der Waals heterostructures, to polar metal-organic frameworks (MOFs), and to the cylindrical pores of covalent organic frameworks (COFs). The presented design ideas are straightforward to simulate and especially for metal-organic interfaces also their experimental implementation has been amply demonstrated. For van der Waals heterostructures, the needed building blocks are available, while the required assembly approaches are just being developed. Conversely, for MOFs the necessary growth techniques exist, but more work on advanced linker molecules is required. Finally, COF structures exist that contain pores decorated with polar groups, but the electrostatic impact of these groups has been largely ignored so far. All this suggest that the dawn of the age of electrostatic design is currently experienced with potential breakthroughs lying ahead.

Real Time Tracking of Nanoconfined Water-Assisted Ion Transfer in Functionalized Graphene Derivatives Supercapacitor Electrodes

Water molecules confined in nanoscale spaces of 2D graphene layers have fascinated researchers worldwide for the past several years, especially in the context of energy storage applications. The water molecules exchanged along with ions during the electrochemical process can aid in wetting and stabilizing the layered materials resulting in an anomalous enhancement in the performance of supercapacitor electrodes. Engineering of 2D carbon electrode materials with various functionalities (oxygen (─O), fluorine (─F), nitrile (─C≡N), carboxylic (─COOH), carbonyl (─C═O), nitrogen (─N)) can alter the ion/water organization in graphene derivatives, and eventually their inherent ion storage ability. Thus, in the current study, a comparative set of functionalized graphene derivatives-fluorine-doped cyanographene (G-F-CN), cyanographene (G-CN), graphene acid (G-COOH), oxidized graphene acid (G-COOH (O)) and nitrogen superdoped graphene (G-N) is systematically evaluated toward charge storage in various aqueous-based electrolyte systems. Differences in functionalization on graphene derivatives influence the electrochemical properties, and the real-time mass exchange during the electrochemical process is monitored by electrochemical quartz crystal microbalance (EQCM). Electrogravimetric assessment revealed that oxidized 2D acid derivatives (G-COOH (O)) are shown to exhibit high ion storage performance along with maximum water transfer during the electrochemical process. The complex understanding of the processes gained during supercapacitor electrode charging in aqueous electrolytes paves the way toward the rational utilization of graphene derivatives in forefront energy storage applications.

Unraveling the Capacitive Behaviors in Nanoconfined Ionophilic Carbon Pores

Intensifying the synergy between confined carbon nanopores and ionic liquids (ILs) and a deep comprehension of the ion behavior is required for enhancing the capacitive storage performance. Despite many theoretical insights on the storage mechanism, experimental verification has remained lacking due to the intricate nature of pore texture. Here, a compressed micropore-rich carbon framework (CMCF) with tailored monolayer and bilayer confinement pores is synthesized, which exhibits a compatible ionophilic interface to accommodate the IL [EMIM][BF4]. By deploying in situ Raman spectroscopy, in situ Fourier-transform infrared spectroscopy, and solid-state nuclear magnetic resonance, the effect of the pore textures on ions storage behaviors is elucidated. A voltage-induced ion gradient filling process in these ionophilic pores is proposed, in which ion exchange and co-ion desorption dominate the charge storage process. Moreover, it is established that the monolayer confinement of ions enhances the capacity, and bilayer confinement facilitates the charging dynamics. This work may guide the design of nanoconfinement carbon for high-energy-density supercapacitors and deepen the understanding of the charge storage mechanism in ionophilic pores.

Plasma Engineering of Co4N/CoN Heterostructure for Boosting Supercapacitor Performance

Supercapacitor electrode materials play a decisive role in charge storage and significantly affect the cost and capacitive performance of the final device. Engineering of the heterostructure of metal-organic framework (MOF)-derived transition metal nitrides (TMNs) can be conducive to excellent electrochemical performance owing to the synergistic effect, optimized charge transport/mass transfer properties, and high electrical conductivity. In this study, a Co4N/CoN heterostructure was incorporated into a nitrogen-doped support by radio-frequency (RF) plasma after simple pyrolysis of Co-based formate frameworks (Co-MFFs), with the framework structure well retained. Plasma engineering can effectively increase the ratio of Co4N in the Co4N/CoN heterostructure, accelerating the electron transfer rate and resulting in a rough surface due to the reduction effect of high-energy electrons and the etching effect of ions. Benefiting from the plasma modification, the obtained electrode material Co4N/CoN@C-P exhibits a high specific capacitance of 346.2 F·g-1 at a current density of 1 A·g-1, approximately 1.7 times that of CoN/Co4N@C prepared by pyrolysis. The specific capacitance of Co4N/CoN@C-P reaches 335.6 F·g-1 at 10 A·g-1, approximately 96.9% of that at 1 A·g-1, indicating remarkable rate capability. Additionally, the capacitance retention remains at 100% even after 1000 cycles, suggesting excellent cycling stability. The rational design and plasma engineering of the TMN heterostructures at the nanoscale are responsible for the excellent electrochemical performance of this novel composite material.

Enhancing Interfacial Capacitance by Boron Doping in Vertically Porous Carbon Toward High-Performance AC Filtering Electrochemical Capacitors

Electrochemical capacitors (ECs) show great perspective in alternate current (AC) filtering once they simultaneously reach ultra-fast response and high capacitance density. Nevertheless, the structure-design criteria of the two key properties are often mutually incompatible in electrode construction. Herein, it is proposed that combining vertically oriented porous carbon with enhanced interfacial capacitance (Ci) can efficiently solve this issue. Theoretically, the density function theory calculation shows that the Ci of a carbon electrode can be enhanced by boron doping due to the corresponding compact induced charge layer. Experimentally, the vertical-oriented boron-doped graphene nanowalls (BGNWs) electrodes, whose Ci is enhanced from 4.20 to 10.16 µF cm-2 upon boron doping, are prepared on a large scale (480 cm2) using a hot-filament chemical vapor deposition technique (HFCVD). Owing to the high Ci and vertically oriented porous structure, BGNWs-based EC has a high capacitance density of 996 µF cm-2 with a phase angle of - 79.4° at 120 Hz in aqueous electrolyte and a high energy density of 1953 µFV2 cm-2 in organic electrolyte. As a result, the EC is capable of smoothing 120 Hz ripples for 60 Hz AC filtering. These results provide enlightening insights on designing high-performance ECs for high-frequency applications.

Surface-Assisted Selective Air Oxidation of Phosphines Adsorbed on Activated Carbon

Trialkyl- and triarylphosphines readily adsorb onto the surface of porous activated carbon (AC) even in the absence of solvents through van der Waals interactions between the lone electron pair and the AC surface. This process has been proven by solid-state NMR techniques. Subsequently, it is demonstrated that the AC enables the fast and selective oxidation of adsorbed phosphines to phosphine oxides at ambient temperature in air. In solution, trialkylphosphines are oxidized to a variety of P(V) species when exposed to the atmosphere, while neat or dissolved triarylphosphines cannot be oxidized with air. When the trialkyl- and triarylphosphines PnBu3 (1), PEt3, (2), PnOct3 (3), PMetBu2 (4), PCy3 (5), and PPh3 (6) are adsorbed in a mono- or submonolayer on the surface of AC, in the absence of a solvent and at ambient temperature, they are quantitatively oxidized to the adsorbed phosphine oxides, 1ox-6ox, once air is admitted. No formation of any unwanted P(V) side products or water adducts is observed. The phosphine oxides can then be recovered in good yields by washing them off of the AC. The oxidation is likely facilitated by a radical activation of molecular oxygen due to delocalized electrons on the aromatic surface coating of AC, as proven by ESR. This easy and inexpensive oxidation method renders hydrogen peroxide or other oxidizers unnecessary and is broadly applicable to sterically hindered and even to air-stable triarylphosphines. Phosphines adsorbed at lower surface coverages on AC oxidize at a faster rate. All oxidation reactions were monitored by solution- and solid-state NMR spectroscopy.

Understanding Electrolyte Ion Size Effects on the Performance of Conducting Metal-Organic Framework Supercapacitors

Layered metal-organic frameworks (MOFs) have emerged as promising materials for next-generation supercapacitors. Understanding how and why electrolyte ion size impacts electrochemical performance is crucial for developing improved MOF-based devices. To address this, we investigate the energy storage performance of Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with a series of 1 M tetraalkylammonium tetrafluoroborate (TAABF4) electrolytes with different cation sizes. Three-electrode experiments show that Cu3(HHTP)2 exhibits an asymmetric charging response with all ion sizes, with higher energy storage upon positive charging and a greater charging asymmetry with larger TAA+ cations. The results further show that smaller TAA+ cations demonstrate superior capacitive performances upon both positive and negative charging compared to larger TAA+ cations. To gain further insights, electrochemical quartz crystal microbalance measurements were performed to probe ion electrosorption during charging and discharging. These reveal that Cu3(HHTP)2 has a cation-dominated charging mechanism, but interestingly indicate that the solvent also participates in the charging process with larger cations. Overall, the results of this study suggest that larger TAA+ cations saturate the pores of the Cu3(HHTP)2-based electrodes. This leads to more asymmetric charging behavior and forces solvent molecules to play a role in the charge storage mechanism. These findings significantly enhance our understanding of ion electrosorption in layered MOFs, and they will guide the design of improved MOF-based supercapacitors.

Toward Ultrahigh-Rate Energy Storage of 3000 mV s-1 in Hollow Carbon: From Methodology to Surface-to-Bulk Synergy Insights

Despite great efforts on economical and functionalized carbon materials, their scalable applications are still restricted by the unsatisfying energy storage capability under high-rate conditions. Herein, theoretical and methodological insights for surface-to-bulk engineering of multi-heteroatom-doped hollow porous carbon (HDPC), with subtly designed Zn(OH)F nanoarrays as the template are presented. This fine-tuned HDPC delivers an ultrahigh-rate energy storage capability even at a scan rate of 3000 mV s-1 (fully charged within 0.34 s). It preserves a superior capacitance of 234 F g-1 at a super-large current density of 100 A g-1 and showcases an ultralong cycling life without capacitance decay after 50 000 cycles. Through dynamic and theoretical analysis, the key role of in situ surface-modified heteroatoms and defects in decreasing the K+-adsorption/diffusion energy barrier is clarified, which cooperates with the porous conductive highways toward enhanced surface-to-bulk activity and kinetics. In situ Raman aids in visualizing the reversibly dynamic adsorption/releasing of the electrolyte ions on the tailored carbon structure during the charge/discharge process. The potential of the design concept is further evidenced by the enhanced performances in water-in-salt electrolytes. This surface-to-bulk nanotechnology opens the path for developing high-performance energy materials to better meet the practical requirements in the future.

Proton-selective coating enables fast-kinetics high-mass-loading cathodes for sustainable zinc batteries

The pressing demand for sustainable energy storage solutions has spurred the burgeoning development of aqueous zinc batteries. However, kinetics-sluggish Zn2+ as the dominant charge carriers in cathodes leads to suboptimal charge-storage capacity and durability of aqueous zinc batteries. Here, we discover that an ultrathin two-dimensional polyimine membrane, featured by dual ion-transport nanochannels and rich proton-conduction groups, facilitates rapid and selective proton passing. Subsequently, a distinctive electrochemistry transition shifting from sluggish Zn2+-dominated to fast-kinetics H+-dominated Faradic reactions is achieved for high-mass-loading cathodes by using the polyimine membrane as an interfacial coating. Notably, the NaV3O8·1.5H2O cathode (10 mg cm-2) with this interfacial coating exhibits an ultrahigh areal capacity of 4.5 mAh cm-2 and a state-of-the-art energy density of 33.8 Wh m-2, along with apparently enhanced cycling stability. Additionally, we showcase the applicability of the interfacial proton-selective coating to different cathodes and aqueous electrolytes, validating its universality for developing reliable aqueous batteries.

A Ferricyanide Anion-Philic Interface Induced by Boron Species within Carbon Framework for Efficient Charge Storage in Supercapacitors

Carbon materials with hierarchical porous structures hold great potential for redox electrolyte-enhanced supercapacitors. However, restricted by the intrinsic inert and nonpolar characteristics of carbon, the energy barrier of anchoring redox electrolytes on the pore walls is relatively high. As such, the redox process at the interface less occurs, and the rate of mass transfer is impaired, further leading to a poor electrochemical performance. Here, a ferricyanide anion-philic interface made of in situ inserted boron species into carbon rings is constructed for enhanced charge storage in supercapacitors. Profiting from the unique component-driven effects, the polar anchoring sites on the pore wall can be built to grasp the charged redox ferricyanide anion from the bulk electrolyte and promote the redox process; the dynamics process is fastened correspondingly. Especially, the boron atoms in BC2O and BCO2 units with higher positive natural bond orbital values in the carbon skeleton are pinpointed as intrinsic active sites to bind the negatively charged nitrogen atoms in the ferricyanide anion via electrostatic interaction, confirmed by density functional theoretical calculations. This will suppress the shuttle and diffusion effects of the ferricyanide anion from the surface of the electrode to the bulk electrolyte. Finally, the well-designed PC-3 with high content of BC2O and BCO2 units can reach 1099 F g-1 at 2 mV s-1, which is a more than 2-fold increase over boron-free units of carbon (428 F g-1). The work offers a novel version for designing high-performance carbon materials with unique yet reaction species-philic effects.

Optimization of Electrode Materials Using Nanocarboxylic Polystyrene Promotes Accumulation for Chromium in Zea mays from Water and Soil Contamination

Chromium is a multivalent metal with great development in the energy storage field because it can effectively improve the electrochemical performance of the material. However, chromium(VI) is soluble in water and toxic, which causes serious metal pollution in the environment. In addition, nanoplastics are difficult to degrade and easy to accumulate, which is an urgent environmental problem to be solved. Therefore, we choose Zea mays to absorb chromium ions, nanopolystyrene, nanocarboxylic polystyrene, and their complexes, which can coordinate and decompose with various polymers in Z. mays, and produce coordination, conjugation, mixed valence, and adjacent group effects. Due to the above effects, the UV-vis spectrum of the material is blueshifted; the X-ray photoelectron spectroscopy peaks of Cr 2p have a chemical shift; the pore structure is optimized; the graphitization degree is improved; the content of N, O, and Cr in the material increases; and the elements are evenly distributed. The series of optimization processes makes the electrodes exhibit excellent electrochemical performance in both supercapacitors and lithium-ion batteries. At 0.5 A·g-1, the specific capacitance of the electrode reaches 490 F·g-1. After 10,000 cycles, its specific capacitance remains at 429.3 F·g-1, and the Coulombic efficiency is 89.9%. In lithium-ion batteries, the initial discharging capacity of the electrode is 1071.7 mAh·g-1 at 0.05 A·g-1. After 5000 cycles, its specific capacity can still reach 242 mAh·g-1 at 0.2 A·g-1, and the Coulombic efficiency is above 95%.

Toward Ultrahigh-Rate Energy Storage of 3000 mV s-1 in Hollow Carbon: From Methodology to Surface-to-Bulk Synergy Insights

Despite great efforts on economical and functionalized carbon materials, their scalable applications are still restricted by the unsatisfying energy storage capability under high-rate conditions. Herein, theoretical and methodological insights for surface-to-bulk engineering of multi-heteroatom-doped hollow porous carbon (HDPC) is presented, with subtly designed Zn(OH)F nanoarrays as the template. This fine-tuned HDPC delivers an ultrahigh-rate energy storage capability even at a scan rate of 3000 mV s-1 (fully charged within 0.34 s). It preserves a superior capacitance of 234 F g-1 at a super-large current density of 100 A g-1 and showcases an ultralong cycling life without capacitance decay after 50 000 cycles. Through dynamic and theoretical analysis, the key role of in situ surface-modified heteroatoms and defects in decreasing the K+ -adsorption/diffusion energy barrier is clarified, which cooperates with the porous conductive highways toward enhanced surface-to-bulk activity and kinetics. In situ Raman further aids in visualizing the reversibly dynamic adsorption/releasing of the electrolyte ions on the tailored carbon structure during the charge/discharge process. The potential of the design concept is further evidenced by the enhanced performances in water-in-salt electrolytes. This surface-to-bulk nanotechnology opens the path for developing high-performance energy materials to better meet the practical requirements in future.

Microscopic Origin of Electrochemical Capacitance in Metal-Organic Frameworks

Electroconductive metal-organic frameworks (MOFs) have emerged as high-performance electrode materials for supercapacitors, but the fundamental understanding of the underlying chemical processes is limited. Here, the electrochemical interface of Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with an organic electrolyte is investigated using a multiscale quantum-mechanics/molecular-mechanics (QM/MM) procedure and experimental electrochemical measurements. Our simulations reproduce the observed capacitance values and reveals the polarization phenomena of the nanoporous framework. We find that excess charges mainly form on the organic ligand, and cation-dominated charging mechanisms give rise to greater capacitance. The spatially confined electric double-layer structure is further manipulated by changing the ligand from HHTP to HITP (HITP = 2,3,6,7,10,11-hexaiminotriphenylene). This minimal change to the electrode framework not only increases the capacitance but also increases the self-diffusion coefficients of in-pore electrolytes. The performance of MOF-based supercapacitors can be systematically controlled by modifying the ligating group.

Bioactive Ion-Based Switchable Supercapacitors

Switchable supercapacitors (SCs) enable a reversible electrically-driven uptake/release of bioactive ions by polarizing porous carbon electrodes. Herein we demonstrate the first example of a bioactive ion-based switchable supercapacitor. Based on choline chloride and porous carbons we unravel the mechanism of physisorption vs. electrosorption by nuclear magnetic resonance, Raman, and impedance spectroscopy. Weak physisorption facilitates electrically-driven electrolyte depletion enabling the controllable uptake/release of electrolyte ions. A new 4-terminal device is proposed, with a main capacitor and a detective capacitor for monitoring bioactive ion adsorption in situ. Ion-concentration control in printed choline-based switchable SCs realizes switching down to 8.3 % residual capacitance. The exploration of adsorption mechanisms in printable microdevices will open an avenue of manipulating bioactive ions for the application of drug delivery, neuromodulation, or neuromorphic devices.