ABSTRACT To design nanostructured electrodes capable of sustaining both high energy and power in sodium‐ion supercapacitors, we present a mechanistically defined synthesis strategy that couples interfacial nano‐pitting of carbon frameworks with in situ sulfate‐substituted crystallization of Na 2.85 V 2 (PO 4 ) 2.85 (SO 4 ) 0.15 (NVPS) nanodots. By integrating phosphate–sulfate ultracentrifugation pretreatment with brief thermal annealing, NVPS nanodots (5 nm) are homogeneously dispersed and tightly anchored along multi‐walled carbon nanotube (MWCNT) networks. Mechanistic analysis revealed that a bifunctional role of Na 2 SO 4 : it induces localized sodification‐assisted etching that forms ≈5 nm nanopits serving as confined nucleation cavities, while sulfate species participate in NVPS crystallization within these domains. Concurrent redeposition of sodified carbon fragments during ultracentrifugation further reinforces interfacial stability, producing nanodots electronically bridged and mechanically stabilized by the carbon matrix. The resulting NVPS/MWCNT composites exhibit exceptional rate capability, delivering 97 mAh g −1 (83% of the theoretical capacity) at 1000C, corresponding to a full charge–discharge cycle of 3.6 s. This ultrafast behavior originates from the formation of robust, strongly coupled nanodot–carbon junctions that facilitate rapid electron transport and sodium‐ion intercalation. This sulfate‐directed nano‐pitting approach provides a generalizable and scalable route to engineer high‐density nanodot/carbon hybrid architectures that bridge the gap between battery‐type and capacitor‐type storage.

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.

Electrophoretic Deposition (EPD) of 8 mol% yttria-stabilized zirconia from a propanol-based suspension were used for the preparation of thick deposits for thermal barrier coating high temperature applications. This work determined a single-layer thickness (for a deposit) near 35 +/- 10 & micro;m, achieved by adapting selected EPD parameters such as applied voltage and waveform, deposit time, suspension concentration, and additives. A multilayer deposition approach followed by a single thermal treatment generated a TBC of total thickness of 200 +/- 20 & micro;m. Slow TGO growth at the HX-NiCrAlY / TBC interface as well as coating thermal resistance and thermal shock longevity were demonstrated. This research represents a step forward in developing EPD-based thermal barrier coatings, a technique compatible with complex geometries.

Surface engineering of carbon electrodes can play a critical role in mitigating interfacial polarization and improving charge-transfer kinetics in aqueous organic redox flow batteries (AORFBs), yet the mechanistic understanding of electrode/electrolyte interactions remains limited. We demonstrate a rational approach to tune the interfacial electrochemical reactivity of graphite felt electrodes through grafting of diazonium salts bearing negatively charged functional groups. The modified surfaces exhibit enhanced hydrophilicity and increased electrochemical capacitance. The impact of surface charge on electron-transfer behavior was systematically investigated using both negatively and positively charged redox probes, revealing a strong dependence of electrochemical activity on electrostatic interactions. While grafted layers partially hindered the ferro/ferricyanide couple, they maintained the reversibility of the [Ru(NH3)6]3+/2+ system, confirming the charge-selective nature of the modified interfaces. When tested in neutral aqueous electrolytes containing nitroxide-based redox mediators, electrodes functionalized with sulfonate groups exhibited improved redox reversibility and reduced polarization. Flow battery tests using 4-OH-TEMPO electrolytes demonstrated up to 15% greater capacity and reduced polarization losses compared to pristine electrodes, particularly at high current densities. These findings establish diazonium chemistry as a versatile and controllable route to tailor electrode/electrolyte interactions in RFBs. Controlled diazonium grafting enhances graphite felt interfaces in AORFB.Surface charge modulates redox kinetics selectively.Grafted felts show improved hydrophilicity and capacitance.Up to 15% higher capacity in nitroxide-based flow cells.

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.

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.

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

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.

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.

Clarifying the relationship between ion desolvation, ion-electrode interactions, and charge storage capacity during ion intercalation in host electrode materials is crucial for advancing fast and efficient energy storage systems. However, the absence of direct evidence for ion desolvation and lack of detailed understanding of the interactions between surface terminations and intercalated cations (Li ions)/solvents hinder the exploration of their effects on energy storage mechanisms. In this paper, we study the intercalation of Li ions from a non-aqueous electrolyte in two-dimensional metal carbides Ti3C2 MXenes with different surface chemistries: HF-Ti3C2 (F-, OH- and O-terminated) and MS-Ti3C2 (O- and Cl-terminated) MXenes. We are able to visualize the full ion desolvation and solvents-ions co-intercalation in the interlayers of MS-MXene and HF-MXene, respectively at the atomic scale. The combination of several techniques and characterization tools reveal that the complete ion desolvation in Cl- and O-terminated MS-Ti3C2 MXenes is associated with the formation of a dense solid electrolyte interface layer, resulting in improved charge storage capacity. The O-rich surface terminations of MS-MXenes are found to be responsible for the efficient Li ions storage. These findings shed lights on identifying the critical role of non-electrostatic ion-electrode interactions and ion desolvation in designing high-performance energy storage devices.

Now that fast action is needed to mitigate the effects of climate change, developing new technologies to reduce worldwide carbon footprint is critical. Sodium ion capacitors can be a key enabler for widespread transport electrification or massive adoption of renewable technologies. However, a years‐long journey needs to be made from the first proof‐of‐concept report to a degree of maturity for technology transfer to the market. To shorten this path, this work gathers all the stakeholders involved in the technical development of the sodium ion capacitor technology, covering the whole value chain from academics (TRL 1‐3) and research centers (TRL3‐5) to companies and end‐users (TRL 6‐9). A 360‐degree perspective is given on how to focus the research and technology development of sodium ion capacitors, or related electrochemical energy storage technologies, from understanding underlying operation mechanisms to setting up end‐user specifications and industrial requirements for materials and processes. This is done not only in terms of performance metrics, but mainly considering relevant practical parameters, i.e., processability, scalability, and cost, leading up to the final sustainability evaluation of the whole of the technology by Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) analysis, which is of utmost importance for society and policymakers.

Confining ionic liquids (ILs) within porous materials offers various opportunities in terms of applications (energy storage, filtration etc), yet precise control of the interaction between the ionic liquid and the matrix remains challenging. Here, we investigate the influence of precursor reaction time during the synthesis of an ionogel coating formed through hybrid sol-gel chemistry, for further use as an electrochemical interface for energy storage applications. Our study reveals significant dependencies of ionic transport properties evaluated by electrochemical impedance spectroscopy on reaction time. By using kinetic monitoring by NMR and SAXS of the precursor during their transformation, we show that the emergence of size controlled nanodomains within the sol can be linked to an enhancement of the interface transport properties. These findings provide valuable insights into the design and optimization of ionogel-based systems for advanced applications in energy storage and membrane technology.

The change in the resistance of the electrode during the polarisation of an electrochemical system, without any contribution from other counterparts of the system, can provide valuable information about various key processes at the material level. Here, we report about the electrochemical characterizations of two-dimensionnal metal carbide materials (Ti3C2 MXenes) using a novel in-plane impedance analysis technique that allows the continuous tracking of the change in the electronic and ionic percolation in the plane of the electrode during the polarisation. The study focuses on the variation of resistance, the formation of the solid electrolyte interphase (SEI), and the intercalation mechanisms during Li-ion intercalation, in different organic electrolytes. Key findings revealed that the effect of the morphology and surface terminations of MXene on the in-plane electronic percolation network of the electrode, which is affected by the SEI layer formation during the first cycle. This study emphasises the significance of surface terminations and synthesis methods of MXenes on their electrochemical performance and, beyond these model materials, shows the opportunities offered by the operando in-plane impedance technique to track the change in the electronic properties of battery electrodes during polarisation. (c) 2025 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, https://creativecommons.org/ licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.

The rising demand for energy storage calls for technological advancements to address the growing needs. In this context, sodium-ion (Na-ion) batteries have emerged as a potential complementary technology to lithium-ion batteries (Li-ion). Among other materials, Na3V2(PO4)2F3 (NVPF) is a promising cathode for Na-ion batteries due to its high operating voltage and good energy density. In order to further characterize the (dis)charge behavior of NVPF, the electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) was employed to track both the frequency and dissipation loss changes at the electrode/electrolyte interface. The electrode composite preparation proved to be crucial for extending the potential window to both Na3V2(PO4)2F3/Na2V2(PO4)2F3 and Na2V2(PO4)2F3/Na1V2(PO4)2F3 domains. Composites prepared with rawNVPF powder (1-20 μm particles) and polyvinylidene fluoride (PVDF) binder (raw-NVPF:PVDF) exhibited large dissipation changes during (dis)charging, attributed to the soft viscoelastic nature of the binder and substantial hydrodynamic interaction caused by the large particles. On the other hand, composites prepared by sieved NVPF particles (<1 μm particles) with sodium carboxymethyl cellulose (NaCMC) binder (sieved-NVPF:NaCMC) showed rigid properties, enabling an extended and more accurate gravimetric analysis. This allowed for the determination of a linear charge-to-mass relationship for the full potential window of NVPF, reflecting the potential independent insertion/deinsertion of bare Na ions (23 g·mol-1). Additionally, reversible dissipative changes were observed for the Na3V2(PO4)2F3/Na2V2(PO4)2F3 transition, with no further dissipative changes observed during the Na2V2(PO4)2F3/Na1V2(PO4)2F3 process.

MXenes are among the fastest-growing families of 2D materials, promising for high-rate, high-energy energy storage applications due to their high electronic and ionic conductivity, large surface area, and reversible surface redox ability. The Ti3C2Tx MXene shows a capacitive charge storage mechanism in diluted aqueous LiCl electrolyte while achieving abnormal redox-like features in the water-in-salt LiCl electrolyte. Herein, various operando techniques are used to investigate changes in resistance, mass, and electrode thickness of Ti3C2Tx during cycling in salt-in-water and water-in-salt LiCl electrolytes. Significant resistance variations due to interlayer space changes are recorded in the water-in-salt LiCl electrolyte. In both electrolytes, conductivity variations attributed to charge carrier density changes or varied inter-sheet electron hopping barriers are detected in the capacitive areas, where no thickness variations are observed. Overall, combining those operando techniques enhances the understanding of charge storage mechanisms and facilitates the development of MXene-based energy storage devices.

Sodium-ion batteries have emerged as a promising secondary battery system due to the abundance of sodium resources. One of the boosters for accelerating the practical application of sodium-ion batteries is the innovation in anode materials. This study focuses on developing a high-performance hard carbon anode material derived from hydroxymethylfurfural, produced from carbohydrates, using a straightforward thermal condensation method. The process results in a unique pseudo-graphitic material with abundant microporosity. Electrochemical evaluations demonstrate excellent sodium storage performance by maintaining the plateau capacity even at higher current densities. This translates to a promising energy density when coupled with the cathode material. However, we also discuss the influence of electrolyte composition on the performance of the hydroxymethylfurfural-derived hard carbon, emphasizing the critical role of electrolyte optimization for the development of efficient and sustainable carbonaceous anode materials for next-generation sodium-based batteries.

Metallic zinc holds promise as a cost-effective and scalable material for secondary energy storage applications. However, its inherent reversibility issues hinder its practical implementation. Among various strategies, interface engineering has emerged as a promising approach to enhance the reversibility of zinc anodes. Herein we introduce an innovative method involving the parallel deposition of poly(acrylic acid) (PAA) and zinc metal, creating a composite layer of polymer and zinc, denoted as Zn-PAA. This unique Zn-PAA layer deposition technique remarkably enhances interfacial behavior, ensuring superior cyclic stability in symmetric cells. Moreover, the Zn-PAA layer reduces polarization effects and effectively mitigates interface alterations during plating and stripping processes resulting in increased interface stability. This study highlights the potential of simultaneous electropolymerisation and zinc deposition as a promising strategy to coat and densify interface on zinc anode with intertangled matrix of zinc and polymer for improving the performance and stability of zinc anodes in batteries.

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.

Understanding the local electrochemical processes is of key importance for efficient energy storage applications, including electrochemical double layer capacitors. In this work, we studied the charge storage mechanism of a model material - reduced graphene oxide (rGO) - in aqueous electrolyte using the combination of cavity micro-electrode, operando electrochemical quartz crystal microbalance (EQCM) and operando electrochemical dilatometry (ECD) tools. We evidence two regions with different charge storage mechanisms, depending on the cation-carbon interaction. Notably, under high cathodic polarization (region II), we report an important capacitance increase in Zn 2+ containing electrolyte with minimum volume expansion, which is associated with Zn 2+ desolvation resulting from strong electrostatic Zn 2+ -rGO interactions. These results highlight the significant role of ion-electrode interaction strength and cation desolvation in modulating the charging mechanisms, offering potential pathways for optimized capacitive energy storage. As a broader perspective, understanding confined electrochemical systems and the coupling between chemical, electrochemical and transport processes in confinement may open tremendous opportunities for energy, catalysis or water treatment applications in the future.