Cation desolvation-induced capacitance enhancement in reduced graphene oxide (rGO)

Dual-function lignin monomers enable high-performance graphene electrodes via interface confinement and proton transfer enhancement

Graphene oxide (GO)-based energy storage faces dual bottlenecks: unsustainable reduction methods and sluggish proton transfer kinetics. Here, we introduce a groundbreaking green strategy using lignin-derived vanillyl alcohol (VA) as a dual-function monomer tosimultaneouslyaddress these challenges. By thermally annealing GO/VA films at mild temperatures (<100 °C), VA triggers an interface-confined reduction of GO while self-polymerizing into redox-active oligomers (P-VA) that intercalate between graphene layers. This dual role-reducing agent and proton highway enables a 3D conductive network with minimized graphene restacking, abundant redox sites, and rapid H+ transport pathways. Density Functional Theory (DFT) reveals how P-VA optimizes proton dynamics, while the resulting rGO-P-VA4-T90 electrode achieves a record volumetric capacitance of 311.1F/cm3 (777.8F/cm2) and retains 87.8 % capacity after 10,000 cycles. Flexible solid-state supercapacitors deliver 94.2 μWh/cm2 energy density at 63.8 μW/cm2, rivaling state-of-the-art devices. This work redefines sustainable graphene engineering, merging biomass valorization with high-performance energy storage in a scalable, eco-friendly paradigm.

Prefilled and Concerted Ion Transport Mechanism in Hierarchical Porous Carbons for Ultra-Fast Energy Storage

Hierarchical porous structures have been extensively reported for their efficiency in achieving fast charging and high energy density in electrochemical capacitors. However, the microscopic dynamic mechanism through which hierarchical pores enhance ion transport and storage remains unclear. Here, we synthesize hierarchical mesopore-micropore carbons with varying mesopore contents of approximately 5 nm in size using a tunable "structure inheritance" strategy for comparative investigation. Advanced constant potential method molecular dynamics simulations and nuclear magnetic resonance spectroscopy are combined with electrochemical analyses to systematically investigate ion behaviors in the hierarchical- and microporous-dominant structures under the driving forces of both constant and cyclic voltages. The results indicate that a prefilled and concerted transport mode is responsible for the enhanced ion transport and storage in the hierarchical mesopore-micropore carbons. Notably, hierarchical pores exhibit a significant fast-charging enhancement, with at least a 50% reduction in response time, across various electrolytes, including aqueous, organic, water-in-salt, and ionic-liquid electrolytes. In all four tested electrolytes, the maximum power density of a typical hierarchical porous carbon is several times that of the microporous carbon. This work provides insights into how hierarchical structures improve ion transport and may promote the development of more efficient electrochemical energy storage materials and devices.

Understanding Multi-Stage Charge Storage on Nanoporous Carbons in Zn-Ion Hybrid Capacitors

Zn-ion hybrid capacitors (ZIHCs) are promising high-power energy storage devices. However, the underlying charge storage mechanisms, especially the influence of proton storage, remain poorly understood. Herein, the model porous carbons are synthesized having similar specific surface areas (SSAs) and surface chemistry but different pore sizes. They highlight the role of supermicropores and small mesopores (0.86-4 nm) enabling a high capacity of 198 mAh g-1 (capacitance of 446 F g-1), while larger mesopores (4-13 nm) significantly enhance cycling stability, exceeding 0.6 million cycles. Electrochemical studies, including EQCM analysis, reveal a 4-stage charge-storage process under cathodic polarization, comprising adsorption and desolvation of hydrated Zn2+ ions, followed by water reduction, catalyzed by Zn2+, and formation of Had. The rising pH leads to the formation of insoluble zinc hydroxysulfate hydrates (ZHS). Depending on the pore architecture, the precipitation of ZHS has different effects on the overall stability of cycling. The study overall: (i) presents a simplified method for pore control in carbon synthesis; (ii) discuss the effect of pore size on charge storage and cycling stability in respect of ZHS formation; (iii) sheds light on the charge storage mechanism indicating the important contribution of cation effect known from electrocatalysis on faradaic charge storage mechanism.

Emerging Issues and Opportunities of 2D Layered Transition Metal Dichalcogenide Architectures for Supercapacitors

Two-dimensional layered transition metal dichalcogenides (2D TMDs) have emerged as promising candidates for supercapacitor (SCs) owing to their tunable electronic properties, layered structures, and effective ion intercalation capabilities. Despite these advantages, challenges such as low electrical conductivity, the interlayer restacking, oxidation and structural collapse hinder their practical implementation. This review provides a comprehensive overview of recent advances in the development of 2D TMDs for SCs. We begin by outlining the charge storage mechanisms and design principles for SCs, followed by an in-depth discussion of the synthesis methods and the associated challenges in fabricating 2D TMD architectures. The subsequent sections explore their crystal structures and reaction mechanisms, illustrating their electrochemical potential in SCs. Furthermore, we highlight material modification strategies, including nanostructuring, defect engineering, phase control, and surface/interface modulation, which have been proposed to overcome existing challenges. Finally, we address critical issues and emerging opportunities for 2D TMDs to inspire the development of SC technologies.

Solvation-mediated adsorption mechanism of solvated lithium ions at a charged solid-liquid interface for electrochemical energy storage: atomic scale investigation and insights

Ion encapsulation by solvent molecules significantly impacts ion transport and the adsorption mechanism in energy storage devices. The aim of this investigation is to analyse the adsorption mechanisms associated with the solvation shell of lithium ions near the electrode/electrolyte interface during the charging process. Simulations using molecular dynamics (MD) are conducted for LiPF6 salt in PC solvent confined in between two flat carbon electrodes. The thermodynamic and physical properties of the simulation show excellent agreement with experimental values. Results indicate that the lithium ion forms a strong tetrahedral solvation structure with PC solvent molecules. Orientation analysis reveals that the polar ends of the solvent molecules in the lithium ion solvation structure are anchored to the positive electrode, which is caused by strong attractive interactions, particularly for high surface charge densities. Meanwhile, the solvation structure and solvent molecules undergo rotation close to the negative electrode at high surface charge densities. These aforementioned phenomena lead to solvation-mediated electrostatic interactions between solvated lithium ions and the electrodes. Finally, the differential capacitance for both positive and negative electrodes decreases under these solvation-mediated electrostatic interactions. This study provides a unique intuitive image of possible implications of the solvation structure on the charging performance of energy storage devices, along with perspectives on developing electrolytes with favorable orientations.

Ultra-Wide Voltage Aqueous Superbatteries Enabled by Iron and Zinc Zeolitic Frameworks

Extensive research on supercapacitor-battery hybrid devices has bridged the gap between conventional batteries and supercapacitors. However, several challenges persist, including limited capacitance in the negative potential range, restricted rate capability, and a narrow potential window (<1.23 V) in aqueous electrolytes. Drawing inspiration from the notable benefits of bottom-up synthesis, which allows tailoring of structure and functionality through the selection of molecular components, we successfully synthesized an Fe-incorporated zeolitic imidazolate framework-8 (composed of Zn nodes and 2-methylimidazole linkers). Subsequently, the metal-organic framework was hydrothermally composited with graphene oxide in the presence of urea to prepare a dual metal oxide/N-doped reduced graphene oxide (DMO-NrGO) nanocomposite. Benefiting from the high hydrogen evolution overpotential of zinc-based compounds and the promising negative potential range activity of iron-based species, the lower potential limit of the X-ray confirmed crystalline-amorphous heterophase DMO-NrGO nanocomposite extends up to -1.45 V. It exhibits a specific capacity (capacitance) of 119 mA h g-1 (378 F g-1) at 1.0 A g-1 in 3.0 M KOH. Interestingly, the symmetric DMO-NrGO based superbattery device demonstrates an ultrawide voltage window of 1.95 V, with a superior specific energy of 28 W h kg-1 and an outstanding specific power of 29 kW kg-1 at 3.0 A g-1. The outstanding electrochemical performance can be attributed to the heterophase structure of the nanocomposite, which accommodates more active sites, provides additional ion transport channels, reduces phase-transformation resistance, and facilitates smooth electron transfer between metal oxides and graphene. This innovative synthetic strategy opens opportunities for developing high-performance aqueous energy storage devices.

Copper-Catalysed Electrochemical CO2 Methanation via the Alloying of Single Cobalt Atoms

The electrochemical reduction of carbon dioxide (CO2) to methane (CH4) presents a promising solution for mitigating CO2 emissions while producing valuable chemical feedstocks. Although single-atom catalysts have shown potential in selectively converting CO2 to CH4, their limited active sites often hinder the realization of high current densities, posing a selectivity-activity dilemma. In this study, we developed a single-atom cobalt (Co) doped copper catalyst (Co1Cu) that achieved a CH4 Faradaic efficiency exceeding 60 % with a partial current density of -482.7 mA cm-2. Mechanistic investigations revealed that the incorporation of single Co atoms enhances the activation and dissociation of H2O molecules, thereby lowering the energy barrier for the hydrogenation of *CO intermediates. In situ spectroscopic experiments and density functional theory simulations further demonstrated that the modulation of the *CO adsorption configuration, with stronger bridge-binding, favours deep reduction to CH4 over the C-C coupling or CO desorption pathways. Our findings underscore the potential of Co1Cu catalysts in overcoming the selectivity-activity trade-off, paving the way for efficient and scalable CO2-to-CH4 conversion technologies.

Strong Replaces Weak: Hydrogen Bond-Anchored Electrolyte Enabling Ultra-Stable and Wide-Temperature Aqueous Zinc-Ion Capacitors

Despite aqueous electrolytes offer a great opportunity for large-scale energy storage owing to their safety and cost-effectiveness, their practical application suffers from the parasitic side reactions and poor temperature adaptability stemming from weak hydrogen-bond (HB) network in free water. Here, we propose the guiding thought "strong replaces weak" to design hydrogen bond-anchored electrolyte by introducing sulfolane (SL) for disrupting the regular weak HB network and contributing to superior temperature tolerance. Judiciously combined experimental characterization and theoretical calculation confirm that SL can remodel the primary solvation shell of metal ions, customize stable electrode interface chemistry and restrain the side reactions. Consequently, symmetric supercapacitor constructed by activated carbon (AC) electrodes is able to fully work within a voltage range of 2.4 V and reach high capacitance retention of 89.8 % after 60000 cycles. Additionally, Zn anodes exhibit ultra-stable Zn plating/stripping behaviors and a wide temperature range (-20-60 °C), and zinc-ion capacitor (Zn//AC) also delivers an excellent cycling stability with capacity retention of 99.7 % after 55000 cycles, implying that the designed electrolyte has practical application potential in extreme environments. This work proposes a novel critical solvation strategy that paves the route for the construction of ultra-stable and wide-temperature aqueous 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.

Effect of Interfacial Electric Field on 2D Metal/Graphene Electrocatalysts for CO2 Reduction Reaction

Understanding the influence of local electric fields on electrochemical reactions is crucial for designing highly selective electrocatalysts for CO2 reduction reactions (CO2RR). In this study, we provide a theoretical investigation of the effect of the local electric field induced by the negative-biased electrode and cations in the electrolyte on the energetics and reaction kinetics of CO2RR on 2D hybrid metal/graphene electrocatalysts. Our findings reveal that the electronic structures of the CO2 molecule undergo substantial modification, resulting in the increased adsorption energy of CO2 on metal/graphene structures, thus reducing the initial barrier of the CO2RR mechanism. This field-assisted CO2RR mechanism promotes CO production while suppressing HCOOH production. Our findings highlight the potential of manipulating electric fields to tailor the pathways of CO2RR, providing new avenues designing selective electrocatalysts.

Investigating the effect of particle size distribution and complex exchange dynamics on NMR spectra of ions diffusing in disordered porous carbons through a mesoscopic model

Ion adsorption and dynamics in porous carbons are crucial for many technologies, such as energy storage and desalination. Nuclear magnetic resonance (NMR) spectroscopy is a key method to investigate such systems thanks to the possibility of distinguishing adsorbed (in-pore) and bulk (ex-pore) species in the spectra. However, the large variety of magnetic environments experienced by the ions adsorbed in the particles and the existence of dynamic exchange between the inside of the particles and the bulk renders the interpretation of the NMR experiments very complex. In this work, we optimise and apply a mesoscopic model to simulate NMR spectra of ions in systems where carbon particles of different sizes can be considered. We demonstrate that even for monodisperse systems, complex NMR spectra, with broad and narrow peaks, can be observed. We then show that the inclusion of polydispersity is essential to recover some experimentally observed features, such as the co-existence of peaks assigned to in-pore, exchange and bulk species. Indeed, the variety of exchange rates between in-pore and ex-pore environments, present in experiments but not taken into account in analytical models, is necessary to reproduce the complexity of experimental NMR spectra.

Tribovoltaic Effect Strengthened Microwave Catalytic Antibacterial Composite Hydrogel

Microwave (MW) therapy is an emerging therapy with high efficiency and deep penetration to combat the crisis of bacterial resistance. However, as the energy of MW is too low to induce electron transition, the mechanism of MW catalytic effect remains ambiguous. Herein, a cerium-based metal-organic framework (MOF) is fabricated and used in MW therapy. The MW-catalytic performance of CeTCPP is largely dependent on the ions in the liquid environment, and the electron transition is achieved through a "tribovoltaic effect" between water molecules and CeTCPP. By this way, CeTCPP can generate reactive oxygen species (ROS) in saline under pulsed MW irradiation, showing 99.9995 ± 0.0002% antibacterial ratio against Staphylococcus aureus (S. aureus) upon two cycles of MW irradiation. Bacterial metabolomics further demonstrates that the diffusion of ROS into bacteria led to the bacterial metabolic disorders. The bacteria are finally killed due to "amino acid starvation". In order to improve the applicability of CeTCPP, It is incorporated into alginate-based hydrogel, which maintains good MW catalytic antibacterial efficiency and also good biocompatibility. Therefore, this work provides a comprehensive instruction of using CeTCPP in MW therapy, from mechanism to application. This work also provides new perspectives for the design of antibacterial composite hydrogel.

Recent Advances in Revealing the Electrocatalytic Mechanism for Hydrogen Energy Conversion System

In light of the intensifying global energy crisis and the mounting demand for environmental protection, it is of vital importance to develop advanced hydrogen energy conversion systems. Electrolysis cells for hydrogen production and fuel cell devices for hydrogen utilization are indispensable in hydrogen energy conversion. As one of the electrolysis cells, water splitting involves two electrochemical reactions, hydrogen evolution reaction and oxygen evolution reaction. And oxygen reduction reaction coupled with hydrogen oxidation reaction, represent the core electrocatalytic reactions in fuel cell devices. However, the inherent complexity and the lack of a clear understanding of the structure-performance relationship of these electrocatalytic reactions, have posed significant challenges to the advancement of research in this field. In this work, the recent development in revealing the mechanism of electrocatalytic reactions in hydrogen energy conversion systems is reviewed, including in situ characterization and theoretical calculation. First, the working principles and applications of operando measurements in unveiling the reaction mechanism are systematically introduced. Then the application of theoretical calculations in the design of catalysts and the investigation of the reaction mechanism are discussed. Furthermore, the challenges and opportunities are also summarized and discussed for paving the development of hydrogen energy conversion systems.

The Polarity of Co-solvents Regulates the Charge Storage Mechanisms in Supercapacitors with Concentrated Electrolytes

Developing better energy storage devices depends on comprehending the underlying mechanisms involved in charge storage. With the continuous conception of new electrolytes, this task becomes progressively more urgent and complex. An example is the utilization of co-solvated concentrated solutions. While these show promising electrochemical responses, their dynamic properties (especially under confinement) and their relationships with performance are not fully understood. Here, we combined modified step potential electrochemical spectroscopy and quasielastic neutron scattering to investigate systems composed of activated mesoporous carbon (AMC) and concentrated solutions of lithium bis(trifluoromethanesulfonyl)imide in acetonitrile co-solvated with either toluene or acetone. We report that acetone does not impair surface-controlled mechanisms, contrary to the case with toluene, which competes with charged species to populate the AMC's pores without contributing to charge storage. In turn, toluene promotes a greater overall capacitance owing to Faradaic processes, which may be related to changes in the solvation structures under confinement.

Interlayer Structure Manipulation of FeOCl/MXene with Soft/Hard Interface Design for Safe Water Production Using Dechlorination Battery Deionization

Suffering from the susceptibility to decomposition, the potential electrochemical application of FeOCl has greatly been hindered. The rational design of the soft-hard material interface can effectively address the challenge of stress concentration and thus decomposition that may occur in the electrodes during charging and discharging. Herein, interlayer structure manipulation of FeOCl/MXene using soft-hard interface design method were conducted for electrochemical dechlorination. FeOCl was encapsulated in Ti3C2Tx MXene nanosheets by electrostatic self-assembly layer by layer to form a soft-hard mechanical hierarchical structure, in which Ti3C2Tx was used as flexible buffer layers to relieve the huge volume change of FeOCl during Cl- intercalation/deintercalation and constructed a conductive network for fast charge transfer. The CDI dechlorination system of FeOCl/Ti3C2Tx delivered outstanding Cl- adsorption capacity (158.47 ± 6.98 mg g-1), rate (6.07 ± 0.35 mg g-1 min-1), and stability (over 94.49 % in 30 cycles), and achieved considerable energy recovery (21.14 ± 0.25 %). The superior dechlorination performance was proved to originate from the Fe2+/Fe3+ topochemical transformation and the deformation constraint effect of Ti3C2Tx on FeOCl. Our interfacial design strategy enables a hard-to-soft integration capacity, which can serve as a universal technology for solving the traditional problem of electrode volume expansion.

Hydrated cation-π interactions of π-electrons with hydrated Mg2+ and Ca2+ cations

Hydrated cation-π interactions at liquid-solid interfaces between hydrated cations and aromatic ring structures of carbon-based materials are pivotal in many material, biological, and chemical processes, and water serves as a crucial mediator in these interactions. However, a full understanding of the hydrated cation-π interactions between hydrated alkaline earth cations and aromatic ring structures, such as graphene remains elusive. Here, we present a molecular picture of hydrated cation-π interactions for Mg2+ and Ca2+ by using the density functional theory methods. Theoretical results show that the graphene sheet can distort the hydration shell of the hydrated Ca2+ to interact with Ca2+ directly, which is water-cation-π interactions. In contrast, the hydration shell of the hydrated Mg2+ is quite stable and the graphene sheet interacts with Mg2+ indirectly, mediated by water molecules, which is the cation-water-π interactions. These results lead to the anomalous order of adsorption energies for these alkaline earth cations, with hydrated Mg2+-π < hydrated Ca2+-π when the number of water molecules is large (n ≥ 6), contrary to the order observed for cation-π interactions in the absence of water molecules (n = 0). The behavior of hydrated alkaline earth cations adsorbed on a graphene surface is mainly attributed to the competition between the cation-π interactions and hydration effects. These findings provide valuable details of the structures and the adsorption energy of hydrated alkaline earth cations adsorbed onto the graphene surface.

Supramolecular metallic foams with ultrahigh specific strength and sustainable recyclability

Porous materials with ultrahigh specific strength are highly desirable for aerospace, automotive and construction applications. However, because of the harsh processing of metal foams and intrinsic low strength of polymer foams, both are difficult to meet the demand for scalable development of structural foams. Herein, we present a supramolecular metallic foam (SMF) enabled by core-shell nanostructured liquid metals connected with high-density metal-ligand coordination and hydrogen bonding interactions, which maintain fluid to avoid stress concentration during foam processing at subzero temperatures. The resulted SMFs exhibit ultrahigh specific strength of 489.68 kN m kg-1 (about 5 times and 56 times higher than aluminum foams and polyurethane foams) and specific modulus of 281.23 kN m kg-1 to withstand the repeated loading of a car, overturning the previous understanding of the difficulty to achieve ultrahigh mechanical properties in traditional polymeric or organic foams. More importantly, end-of-life SMFs can be reprocessed into value-added products (e.g., fibers and films) by facile water reprocessing due to the high-density interfacial supramolecular bonding. We envisage this work will not only pave the way for porous structural materials design but also show the sustainable solution to plastic environmental risks.