Millisecond spray drying enables overcoming the immiscibility gap in solid-solution, forming a supersaturated metastable phase of Li 3 VO 4 –Li 2 MoO 4 for high-power Li-ion storage.

Sodium-ion batteries are considered a promising and sustainable energy-storage technology, yet achieving competitive energy density requires electrode materials with high reversible capacity. Here, we introduce a chemical vapor deposition strategy that allows the growth of uniform, electronically continuous carbon coatings onto highly porous carbon substrates for use as high-capacity negative electrodes. This coating narrows and partially seals the open pore network, suppresses surface reactivity, and establishes nanoconfined domains that allow sodium to be stored in a more compact manner. This restructuring significantly enhances sodium storage performance, delivering total reversible capacities exceeding 500 mAh g-1 together with an unprecedented 420 mAh g-1 reversible plateau capacity. By enabling control over heteroatom composition, confinement, and electronic structure, this approach not only addresses the challenge of designing uniform and electronically continuous carbon coatings on highly porous substrates but also establishes a general route for designing functional carbon films for advanced electrodes, catalysts, and interfaces with tunable electronic properties.

Doping pseudocapacitive transition metal oxides with metal cations has been demonstrated to enhance the electrochemical performance of the resulting electrode materials, particularly in terms of capacitance, rate capability, and cycling stability. In this study, a straightforward synthetic approach was employed to prepare Cu 2+ -modified birnessite δ -MnO 2 powders, where the composition was systematically varied by adjusting the concentration of CuSO 4 solution and the treatment temperature. The electrochemical behavior of these materials in various aqueous electrolytes was found to be highly dependent on the synthesis conditions. Optimal parameters—specifically, a CuSO 4 concentration of 1 M and a treatment temperature of 50 °C—yielded the material with the highest Cu 2+ loading, exhibiting a capacitance of 127 F g −1 at 0.5 A g −1 in a 6 M KOH electrolyte. Furthermore, this electrode material achieved a capacitance of 151 F g −1 at 2 A g −1 and 106 F g −1 at 10 A g −1 in a 1 M Na 2 SO 4 electrolyte, corresponding to a remarkable rate retention of 73%. The observed enhancement in electrochemical performance was attributed to the increased morphological opening induced by Cu 2+ treatment. When paired with activated carbon as the negative electrode in a full-cell configuration, the asymmetric supercapacitor delivered an energy density of 22 Wh kg −1 at a power density of 450 W kg −1 , significantly surpassing the performance of devices based on pristine δ -MnO 2 . These findings underscore the efficacy of Cu 2+ incorporation in MnO 2 -based materials for supercapacitive energy storage applications.

Herein, p-type delafossite CuCrO2 catalysts were synthesized at various calcination temperatures (900, 1000, 1100, and 1200 degrees C), then characterized and evaluated for hydrogen production through photocatalytic methods, with an optimization of the reaction medium. Their textural and structural characteristics were assessed using various physicochemical methods, including XRD, BET, SEM-EDS, and XPS. Optical and electrochemical properties were also evaluated by UV-visible spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and capacitance-potential measurements (Mott-Schottky analysis). It was shown that calcination temperature has a significant effect on these structural, textural, optical, and electrochemical properties, as well as on the materials' reactivity. The 3-R delafossite CuCrO2 structure was obtained starting from 900 degrees C, with crystallite sizes almost independent of calcination temperature. Electrochemical studies confirmed the p-type nature of all samples. Optical, physical, and photoelectrochemical parameters were correlated to construct the energy diagram for evaluating the CuCrO2 delafossite's ability to produce H2. In a neutral medium (Na2SO4), the best activity was attributed to the preparation calcined at 1200 degrees C (CC1200) attributed to its structural and electrochemical stability, while in a basic medium (NaOH), the catalyst calcined at 1100 degrees C (CC1100) produced the highest amount of H2, combining a small crystallite size and a bandgap conducive to efficient light absorption.

Green, scalable and efficient synthesis methods are critical for advancing MXene research and practical applications. However, the production of delaminated MXenes still relies on complex multistep processes to achieve both selective etching and delamination. Here we propose a single-step strategy to directly transform MAX phases into delaminated MXenes using a deep eutectic solvent (DES) based on cobalt chloride/choline chloride (CoCl2 & centerdot;6H2O/ChCl). This system combines a redox process between Lewis acidic salts and A-site elements with an expansion effect from organic ligand decomposition, enabling integrated etching, delamination and surface functionalization. The DES-derived MXenes exhibit unique surface chemistry with -Cl, -O and -NHyR1-y terminations, delivering exceptional lithium-ion storage performance (451 mAh g-1 at 0.05 A g-1). Notably, this approach yields MXenes with positively charged surfaces, suppressing anionic polyiodide shuttling in zinc-iodine batteries. The resulting batteries retain 146 mAh g-1 capacity after over 60,000 cycles at 10 A g-1. This work provides an environmentally friendly and scalable route to delaminated MXenes, integrating structural control with interfacial engineering, and expands their versatility in energy storage and beyond.

Supercapacitors are energy storage devices characterized by fast charging capabilities. The discovery of enhanced capacitance in nanoporous carbons radically challenged the understanding of their charging mechanism, sparkling the development of in situ characterization methods and computational modeling techniques. However, the microscopic origin of this effect remains debated: The importance of pore size on the capacitance put forward in the seminal study was recently questioned in a work focusing on the carbon disorder. Here we close this debate by reconciling these apparently conflicting perspectives. We demonstrate that, at fixed disorder, capacitance does indeed increase with decreasing pore size. Our conclusions are enabled by molecular dynamics simulations methodological advances, that overcome long-standing limitations and yield quantitative agreement with electrochemical measurements. By bridging the gap between earlier observations and recent interpretations, our study provides a unified framework for understanding capacitance in nanoporous materials and offers guidelines for the design of nextgeneration supercapacitors.

Reduced graphene oxide (rGO) has been widely studied as active material for supercapacitor electrodes. However, rGO is generally derived from graphene oxide reduction, and the different reduction methods result in varying electrochemical performances. The aim of this work is to study these various rGOs and correlate their physico-chemical properties to their electrochemical performance in aqueous acidic electrolyte. Therefore, different rGOs have been prepared using i) chemical reduction involving hydrazine hydrate or ii) L-Ascorbic Acid and iii) hydrothermal reduction. We demonstrate that capacitance is governed by surface chemistry, notably carbonyl group content, which determines interfacial charge storage mechanisms. This study show that hydrazine-reduced rGO, although exhibiting the highest SSA, reduction degree, and conductivity, has the lowest carbonyl content and capacitance. The highest capacity is displayed by the rGO reduced hydrothermally, characterized by a low degree of reduction and the highest amount of carbonyl groups. This is in good agreement with the reactivity of these moieties in acidic media, giving rise to an increase of the pseudo-capacitance. The investigation of the storage mechanism using classical EQCM and advanced ac-electrogravimetric analysis showed multi-species involvement (H+, SO42-, HSO4- ions and free H2O molecules), and allowed their amount and flux dynamics to be extrapolated. The interfacial charge compensation mechanism is impacted by carbonyl content, as evidenced by significant H+ involvement and slower interfacial kinetics arising from additional faradaic processes. These results emphasize that, in acidic electrolyte, rGO surface chemistry governs electrochemical performance and behavior, and that surface redox reactions determine the nature of exchanged species.

Here we investigated the electrochemical performance of molybdenum nitride films as an efficient electrode for asymmetric micro-supercapacitors. Molybdenum nitride films were successfully deposited and optimized by reactive magnetron sputtering. On the one hand, the tuning of several deposition parameters (pressure, gas flow rates) allows obtaining molybdenum nitride electrode with high porosity and high electrical conductivity. On the other hand, Operando X-ray diffraction, operando Raman spectroscopy and operando X-ray absorption spectroscopy are combined to unveil the charge storage process in 1 M KOH aqueous electrolyte. These measurements clearly reveal the role of molybdenum oxide species in the pseudocapacitive mechanism at the oxide/electrolyte interface. High volumetric capacitance up to 624 F & sdot;cm-3 with excellent capacitance retention of 95 % over 20 000 cycles was achieved in 1 M KOH.

With the rapid development of two-dimensional MXene materials, numerous preparation strategies have been proposed to enhance synthesis efficiency, mitigate environmental impact, and enable scalability for large-scale production. The compound etching approach, which relies on cationic oxidation of the A element of MAX phase precursors while anions typically adsorb onto MXene surfaces as functional groups, remains the main prevalent strategy. By contrast, synthesis methodologies utilizing elemental etching agents have been rarely reported. Here, we report a new elemental tellurium (Te)-based etching strategy for the preparation of MXene materials with tunable surface chemistry. By selectively removing the A-site element in MAX phases using Te, our approach avoids the use of toxic fluoride reagents and achieves tellurium-terminated surface groups that significantly enhance sodium storage performance. Experimental results show that Te-etched MXene delivers substantially higher capacities (exceeding 50% improvement over conventionally etched MXene) with superior rate capability, retaining high capacity at large current densities and demonstrating over 90% capacity retention after 1000 cycles. This innovative synthetic strategy provides new insight into controllable MXene preparation and performance optimization, while the as-obtained materials hold promises for high-performance sodium-ion batteries and other energy storage systems.

Battery-like organic materials including quinone-based electrodes with electrochemical activity have been extensively investigated for their use as electrode materials in energy storage devices due to their economic competitiveness and sustainable benefits. However, the intrinsic electrical insulating nature of organic quinones and their electrochemical reactivity limit power capability and stability upon charge/discharge cycling, respectively. Here, we report the preparation of a concentric layered architecture, MXene/Anthraquinone/Carbon Cloth (M/AQ/CC), by physisorption of anthraquinone onto the surface of carbon cloth via non-covalent pi-pi interactions, followed by dipping in exfoliated MXene suspension. The M/AQ/CC electrode, with a high mass loading (18.2 mg cm-2), delivered a capacity of 46 mAh g-1 (about 1 mAh cm-2 areal capacity or 6 mAh ml-1 volume) at 0.5 A g-1, with good rate performance and an enhanced cyclability over 5 k cycles. This simple preparation method can also be applied to incorporate MXene with a series of alternative organic redox carriers on freestanding carbon cloth, including thionin acetate and anthraquinone-2-sulfonate. The improvement in electrochemical performance highlights an efficient approach to store more charges via redox reactions from organic quinones pi-stacked at carbon surfaces, thanks to a protective MXene shield that stabilizes the Faradaic behavior of quinones over repetitive charge-discharge processes. The simplicity and versatility of this method should enable design of many advanced electrode materials based on MXene/quinones/carbon cloth for power devices.

Electric double-layer capacitors (EDLCs), or supercapacitors, are high-performance energy storage devices known for their superior power density, rapid charge-discharge capabilities, and long cycle life. The electrolyte composition, specifically the choice of solvent and salt, plays a critical role in determining the voltage range, energy efficiency, and cycle lifespan of EDLCs. This study explores the novel electrolyte spiro1,1'-bipyrolidinium tetrafluoroborate (SBPBF4), selected for its high solubility and outstanding electrochemical stability at elevated voltages. SBPBF4, with its unique cyclic structure among quaternary ammonium salts, offers advantages particularly suited for high-voltage applications. This study investigates SBPBF4 in low-viscosity solvents, namely acetonitrile (AN) and dimethyl carbonate (DMC), chosen for their complementary properties that could further enhance SBPBF4's performance. A central focus is on the electrolyte's impact on stability and gas generation in both symmetrical AC//AC and hybrid LTO//AC configurations. Findings indicate that SBPBF4 enhances float durability and minimizes gas generation, an effect attributed to the resistance of the SBP+ cation to Hofmann elimination. This resistance interrupts degradation cycles typically triggered by interactions between residual water and solvents, stabilizing the electrolyte and preventing reductive decomposition at the negative electrode surface. Understanding these mechanisms is essential for optimizing low-viscosity solvent-based electrolytes and ensuring reliable operation in EDLCs and hybrid supercapacitors.

Cation-disordered materials offer attractive potential for high-power energy storage by unlocking diversified ionic transport pathways, yet their practical realization remains challenging due to difficulties in stabilizing disorder. Here, we demonstrate spray-drying as a direct and scalable route to synthesize cation-disordered Li3VO4 without requiring postannealing or additional lithiation steps. By leveraging ultrafast solvent removal, this method induces flash crystallization in less than 1 s, kinetically "freezing" the metastable disordered phase. Structural analysis using synchrotron X-ray diffraction, Pair-Distribution Function analysis, and high-resolution Transmission Electron Microscopy reveals that ultrafast drying disrupts long-range cation ordering while preserving short-range periodicity, forming local cation-ordered domains within an average disordered structure. This nanoscale disorder, stabilized by antiphase domain boundaries, enhances lithium-ion diffusivity, delivering a high-power performance of 138 mAh g-1 at a 60C rate. By enabling precise control of cation disorder through drying kinetics, this study establishes spray-drying as a powerful and scalable platform for next-generation energy storage materials.

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 Zn 2+ ions, followed by water reduction, catalyzed by Zn 2+ , and formation of H ad . 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.

MXenes are a versatile family of 2D materials with promising energy storage capabilities arising from their high electronic and ionic conductivity, large surface area, and potential for reversible surface redox processes. 1,2 Ti 3 C 2 T x MXene (T being =O, –OH, –Cl or –F terminations) exhibits distinct electrochemical behavior depending on the nature of the electrolyte. On one hand, in acidic electrolyte, Ti 3 C 2 T x displays pseudocapacitive behavior based on the Ti as redox center, involving proton exchange between the electrolyte and its surface terminations. 3,4 In contrast, it shows purely capacitive behavior in neutral to basic solutions, as well as in organic or ionic liquid electrolytes. 5,6 Furthermore, an intriguing behavior has been reported in LiCl water-in-salt (WIS) concentrated electrolyte, with the apparition of reversible surface-controlled redox-like behavior during Li + intercalation/deintercalation. 7,8 Using the combination of different operando techniques, including Electrochemical Quartz Crystal Microbalance (EQCM), Electrochemical Dilatometry (ECD) and in-plane resistance measurement, 9,10 we tracked the evolution of mass, thickness and electronic resistance of the Ti 3 C 2 T x MXene in both LiCl WIS and salt-in-water (SIW) diluted LiCl electrolytes to elucidate the charge storage mechanisms. Results show that different behaviours are observed in both cases, highlighting the key role of the MXene surface chemistry / electrolyte interactions. The study highlights the power of advanced operando techniques to further understand the charge/discharge storage mechanism of energy storage materials. A. VahidMohammadi, J. Rosen, and Y. Gogotsi, Science , 372 , eabf1581 (2021). Y. Gogotsi, Chem. Mater. , 35 , 8767–8770 (2023). C. Zhan et al., J. Phys. Chem. Lett. , 9 , 1223–1228 (2018). X. Mu et al., Adv. Funct. Mater. , 29 , 1902953 (2019). M. R. Lukatskaya et al., Science , 341 , 1502–1505 (2013). Z. Lin et al., Electrochemistry Communications , 72 , 50–53 (2016). X. Wang et al., ACS Nano , 15 , 15274–15284 (2021). D. Zhang, R. Wang, X. Wang, and Y. Gogotsi, Nat Energy , 8 , 567–576 (2023). V. Maurel et al., J. Electrochem. Soc. , 169 , 120510 (2022). A. Perju et al., J. Electrochem. Soc. , 171 , 110511 (2024). Figure 1

In this work, we aim to explore the synergetic influence of the functionalization of the carbon electrode and that of the electrolyte pH on the charge storage mechanism by utilizing the technique of EQCM (Electrochemical Quartz Crystal Microbalance). A comparative analysis has been carried out on YP50 and o-YP50 (carbon with oxygen functionalities), which revealed crucial differences in the evolution of ionic contribution to charge storage under varying pH. A progression from anionic to cationic mechanism was observed with an increase in pH, depending on the isoelectric point of the carbon under study. A combination of TPD-MS (Temperature Programmed Desorption Mass Spectrometry) and EQCM was used to probe pH-dependent surface transformations occurring on the functionalized and non-functionalized carbon electrode during electrochemical cycling. The electrolyte pH governs the protonation state of the surface functional groups, which influences the charge on the electrode and hence the mechanism of charge storage.

Transport of electrons and ions at carbon surfaces immersed in electrolytes is instrumental for a wide variety of membrane processes as well as energy storage in batteries and supercapacitors. Ion transport in a nanoporous electrode strongly depends on its electronic conductance and on the interfacial capacitance with the electrolyte. In this study, we use in-plane impedance spectroscopy to disentangle in-plane ionic and electronic transport on a single crystal graphene transistor covered by an ionic liquid droplet (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, EMI-TFSI). droplet. Due to the atomic thickness of graphene combined to the strong affinity of EMI+ for carbon, this transistor maximizes ion–electron couplings. Using gate- and temperature-dependent in-plane spectroscopy, we extract both the electronic and ionic conductance of the transistor on a wide range of charge carrier density and over several decades of electrolyte conductivity. We show that despite an exceptionally high capacitive coupling at the carbon–EMI-TFSI interface, the ionic and electronic transport pathways are decoupled at the micrometric scale, in agreement with predicted lengthscales involved in the electronic-ionic interfacial transport.

Self-supported carbon monoliths offering hierarchically organized porosity have been synthesized while coupling a silica-monolith-based hard template and a butane-based (a nonreprotoxic alternative to phenolic resins) chemical vapor infiltration method. Final materials are obtained in a self-standing state and not as powder, thereby avoiding flowability. As such good mechanical properties are reached addressing 0.25 MPa of stress at break and 0.0015 MPa Young's modulus. Observations through TEM and HRTEM show that the carbon monoliths are made of interconnected carbonaceous multilamellar-concentric spheres, resulting in a three-dimensional porous network at a higher length scale. The high porosity (90% vol) of the final materials and the interconnected porous network are not detrimental to the monoliths' mechanical cohesion. This material also exhibits a good thermal stability in a nonreducing atmosphere, where 500 degrees C is necessary to combust the monolith carbonaceous backbone, revealing aside the material's excellent purity (heteroatoms' free). In that concern, both XRD and Raman investigations demonstrate that the carbonaceous network has a good graphitic nature. N2 BET physisorption investigations show that chemical vapor infiltration appears as a realistic method of generating a microporous carbonaceous self-standing material (0.28 cm3/g micropore volume) while offering 920 m2/g of specific surface area. Finally, cyclic voltammetry and electrical impedance measurements evidenced a stable and reasonable restituted capacity of 92 F/g after 1000 cycles.

This study develops a highly densified bronze‐type TiO₂ (TiO 2 (B)) anode to enhance the volumetric energy and power density of supercapacitors. By integrating ultracentrifugation with strategic carbon reduction via annealing, a TiO₂(B) anode with fluid‐like lubrication, high compressibility, and improved electrode density is synthesized. The annealing process facilitated a hierarchical nanoporous TiO₂(B) network while preventing agglomeration, achieving an electrode density of 2.24 g cm⁻ 3 , surpassing conventional values. The densified electrode exhibited an exceptional volumetric capacity of 400 mAh cm⁻ 3 , maintaining high‐rate performance at 120C. This approach effectively links mechanical and physicochemical properties to electrochemical performance, offering a scalable strategy for optimizing TiO₂(B) anodes. The findings highlight the potential of highly densified TiO₂(B) for hybrid supercapacitors, particularly in applications requiring maximum energy and power density within compact volumes. These advancements hold promise for electric mobility, portable electronics, and renewable energy storage, where efficiency and performance are critical. By demonstrating a method for achieving high‐density energy storage, this study provides a framework for next‐generation supercapacitor materials. Addressing the growing demands of modern technologies, this research advances high‐performance, space‐efficient energy storage solutions crucial for future energy applications

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 higher energy storage upon positive charging and an asymmetric charging response with all ion sizes, with a greater charging asymmetry with larger TAA+ cations. The results further show that smaller TAA+ cations demonstrate superior capacitive performance upon both positive and negative charging compared to larger TAA+ cations. To gain further insights, electrochemical quartz crystal microbalance (EQCM) measurements were performed to probe the ion electrosorption during charging. These reveal that Cu3(HHTP)2 has a cation-dominated charging mechanism, but interestingly indicate that the solvent also participates in the charging mechanism with larger cations. Overall, the results of this study suggest that larger TAA+ cations saturate the pores of the Cu3(HHTP)2-based electrodes, leading to more asymmetric charging and forcing solvent molecules to play a role in the charge storage mechanism. These findings significantly enhance our understanding of ion electrosorption in layered MOFs, and will guide the design of improved MOF-based supercapacitors.

Due to their high energy density, Li-ion batteries have become the preferred choice for consumer electronics, transportation, and other applications. Current collectors, which are needed for injecting/removing electrons into/from the active material, play a crucial role in the performance of these batteries, influencing capacity, rate capability, and long-term stability, but they receive much less attention. Over the years, there has been a trend of decreasing the thickness of the current collectors to enhance energy density by reducing the weight of the battery. This study focuses on substituting the conventional copper current collector with a thinner and lighter MXene film for high-mass-loading graphite anodes of Li-ion batteries. We also demonstrate the sustainability of our approach to the electrode design by recycling and reusing the MXene current collector after initial use. Our results show improved performances of electrodes using Ti3C2Tx MXene current collectors with reduced total electrode weight and thickness. The electrode-level gravimetric capacity increased by almost 130 mA h g-1, reflecting an 89% increase.