Energy Storage Technologies Research Articles

A voltage-decoupled Zn-Br2 flow battery for large-scale energy storage

The flow battery represents a highly promising energy storage technology for the large-scale utilization of environmentally friendly renewable energy sources. However, the increasing discharge power of rechargeable battery results in a higher charge voltage due to its coupling relationship in charge-discharge processes, intensifying the burden of renewable energy power systems. Herein, we proposed a voltage-decoupled Na+-conducting Zn-Br2 flow battery (Ud-Na-ZBFB). Within a pH-regulation strategy, both neutral Zn/Zn2+ and alkaline Zn/Zn(OH)42− negative redox couples are integrated into one device, so as to increase discharge voltage a 0.5 V theoretical increase while remains a low charge voltage. The proof-of-concept Ud-Na-ZBFB demonstrates an unprecedented voltage characteristic, achieving a discharge voltage of up to 2.18 V while maintaining a remarkably low charge voltage of 1.78 V at a current density of 20 mA cm−2. Benefiting from the high discharge voltage, the peak power density of Ud-Na-ZBFB reaches 580 mW cm−2, nearly twice higher than the traditional ZBFB. Besides, the Ud-Na-ZBFB cycling operates for 45 h with excellent stability and resilience. With the “cycle-to-stage” operational mode, battery state of Ud-Na-ZBFB can be completely recovered after a long-term operation stage with several cycles, which electrolyte utilization efficiency of one stage is up to 41 %. This work offers a brand-new utilization pattern for high-power rechargeable battery that possesses a great potential in energy storage application scenes.

Life Cycle of LiFePO4 Batteries: Production, Recycling, and Market Trends.

Significant attention has focused on olivine-structured LiFePO4 (LFP) as a promising cathode active material (CAM) for lithium-ion batteries. This iron-based compound offers advantages over commonly used Co and Ni due to its lower toxicity abundance, and cost-effectiveness. Despite its current commercial use in energy storage technology, there remains a need for cost-effective production methods to create electrochemically active LiFePO4. Consequently, there is ongoing interest in developing innovative approaches for LiFePO4 production. While LFP batteries exhibit significant thermal stability, cycling performance, and environmental benefits, their growing adoption has increased battery disposal rates. Improper disposal practices for waste LFP batteries result in environmental degradation and the depletion of valuable resources. This review comprehensively examines diverse synthesis approaches for generating LFP powders, encompassing conventional methodologies alongside novel procedures. Furthermore, it conducts an in-depth assessment of the methodologies employed in recycling waste LFP batteries. Moreover, it emphasizes the importance of LFP cathode recycling and investigates pretreatment techniques to enhance understanding. Additionally, it provides valuable insights into the recycling process of used LFP batteries, aiming to raise awareness regarding the market for retired LFP batteries and advocate for the enduring sustainability of lithium-ion batteries.

Anionic Solvation Transition at Low Temperatures for Reversible Anodes in Lithium-Oxygen Batteries.

Li-O2 batteries provide a novel technology for electric energy storage due to their high energy density. However, the strong solvent coordination with Li+ at low temperatures impacts their performance and triggers irreversible interfacial reactions on the Li anode. Herein, cyclopentyl methyl ether (CME) is incorporated in a dimethoxyethane (DME)-based electrolyte to realize an anionic solvation transition at low temperatures in Li-O2 batteries. CME featuring a single O coordination site substitutes highly solvating DME in the first solvation sheath, and it induces more anion coordination to Li+ across the room- and low-temperature ranges. The low residence time of CME (66 ps at 25 °C, 382 ps at -40 °C.) in the solvation structures leads to the fast exchange of coordinated CME molecules with Li+ in comparison with DME and facilitates Li+ desolvation at low temperatures. The simultaneously generated inorganic-rich solid electrolyte interphase promotes Li+ transport to improve Li deposition and suppress Li dendrite formation. These enable the Li-O2 battery to present a good cycling stability of 110 cycles with a fixed capacity of 1000 mA h g-1 at -40 °C. This work paves the way for designing novel electrolytes in low-temperature batteries.

Thermodynamic analysis and optimization of the TI-PTES based on ORC/OFC with zeotropic mixture working fluids

Thermal Integrated Pumped Thermal Energy Storage (TI-PTES) is a promising technology for large-scale energy storage attributed to the advantages of geographical independence, high efficiency, low cost, and easy coupling with other systems. Little research has been dedicated to TI-PTES based on the organic flash cycle (OFC). This study established thermodynamic analysis of the TI-PTES based on the organic Rankine cycle (ORC) and OFC. The effects of system configurations and key parameters are explored. A multi-objective optimization is introduced to optimize the ORC-TI-PTES, and the P2P efficiency of 57.18 %, exergy efficiency of 37.47 %, and ESD of 4.4 kWh/m3 are achieved. The potential application of zeotropic mixture working fluids in the OFC-TI-PTES is investigated. The DOFC-TI-PTES with [R365mfc(60 wt%) + R1234ze(Z)] shows the best performance among the four OFC configurations. The achieved P2P efficiency and exergy efficiency are 46.66 % and 29.18 %, lower than the ORC-TI-PTES. However, the DOFC-TI-PTES provides an ESD of 11.487 kWh/m3, which is significantly higher than that of the ORC-TI-PTES. ORC-TI-PTES is suitable for energy storage applications that prioritize high thermal and exergy efficiencies, whereas OFC-TI-PTES is suitable for scenarios requiring high ESD.

Computational screening of transition metal atom doped ZnS and ZnSe nanostructures as promising bifunctional oxygen electrocatalysts.

The design of bifunctional oxygen electrocatalysts showing high catalytic performance for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great significance for developing new renewable energy storage and conversion technologies. Herein, based on the first principles calculations, we systematically explored the electrocatalytic activity of a series of transition metal atom (Fe, Co, Ni, Cu, Pd and Pt)-doped ZnS and ZnSe nanostructures for OER and ORR. The calculated results revealed that Ni- and Pt-doped ZnS and ZnSe nanostructures exhibit promising electrocatalytic performance for both OER and ORR in comparison to the pristine ZnS and ZnSe nanostructures. Especially, the OER/ORR overpotentials of Ni-doped ZnS and ZnSe nanostructures are estimated to be 0.28/0.30 and 0.31/0.31 V, respectively, disclosing their great potential as bifunctional oxygen electrocatalysts. Moreover, it is found that Ni-doped ZnS and ZnSe nanostructures for OER and ORR are on the top of the volcano plots, evincing promising catalytic performance. Our results provide theoretical insights into a feasible strategy to synthesize highly efficient ZnS- and ZnSe-based bifunctional oxygen electrocatalysts in the future.

Hybrid Core-Shell TiCN@SiO2 Nanoparticles in Percolation-Based Polyvinylidene Fluoride Dielectrics for Improved High-Voltage Capacitive Energy Storage.

Solid-state polymer dielectrics offer an exceptional dielectric breakdown, but require an enhanced energy density to be competitive with alternative electrolyte-based energy storage technologies. Therefore, this research introduces conductive titanium carbonitride (TiCN) nanoparticles in a polyvinylidene fluoride (PVDF) matrix to obtain flexible percolation-based nanodielectrics by ultrasonication-based suspension processing and hot pressing. Well-dispersed TiCN nanoparticles in PVDF were obtained for a wide range of filler volume fractions, and an exceptional peak in the dielectric constant equal to 1130 (0.1 Hz) and 29 (10 kHz) was observed near the percolation threshold (9.2 vol %). The enhanced dielectric constant was ascribed to massive interfacial polarization occurring, resulting from Maxwell-Wagner-Sillars (MWS) polarization and a nanocapacitor mechanism that are dominant at low and high frequencies, respectively. An improvement by 30% in the energy density (0.042 Wh kg-1) compared with the neat PVDF matrix was achieved for the PVDF/TiCN nanodielectrics. The first successful uniform deposition of a nanometer-thin (3 nm) silica (SiO2) shell via the Stöber process on TiCN nanoparticles significantly suppressed the dielectric losses near percolation for the PVDF/TiCN@SiO2 nanodielectrics by more than 1 order of magnitude while offering dielectric constants of 34 (0.1 Hz) and 10 (10 kHz). This study demonstrates the potential of hybrid (core-shell) percolation-based dielectrics for an improved capacitive dielectric performance by an integrated dielectric characterization approach that simultaneously optimizes the dielectric constant, loss tangent, breakdown strength, and energy density.

Fluorinated ester additive to regulate nucleation behavior and interfacial chemistry of room temperature sodium-sulfur batteries

Room temperature sodium-sulfur (RT Na-S) batteries are considered as advanced energy storage technology due to their low cost and high theoretical energy density. However, challenges such as the growth of sodium dendrite and dissolution of sodium polysulfides significantly hinder the electrochemical performance. Herein, we developed a propylene carbonate (PC)-based electrolyte with Methyl 2-Fluoroisobutyrate (MFB) as an additive. The ester group in the MFB additive is capable of participating in and reconfiguring the coordination of their Na+ solvated structures, thereby lowering the desolvation barrier and regulating the Na anode’s interfacial reaction and nucleation behavior. The polar C−F bond at the other end helps to reduce the lowest unoccupied molecular orbital (LUMO) energy of the MFB additive, enabling the preferential decomposition of MFB to form the F-rich inorganic phase strong polar solid electrolyte interphase (SEI), contributing to the inhibition of Na dendrite growth, the accumulation of dead Na. In addition, NaF-riched cathode electrolyte interphase (CEI) was also observed on sulfur-based cathode, which can effectively inhibited the shuttle effect. Consequently, the developed RT Na-S battery exhibit excellent electrochemical performance.

Synergistic Enhancements of Zn-ZIF with Nano Zinc Oxide for Hydrogen adsorption, energy storage, and photocatalytic technologies

Creating the porous Zinc-Zeolitic Imidazolate Framework (Zn-ZIF) using a solvothermal technique addresses the need for advanced materials with distinctive properties and cost-effectiveness in modern applications. The PXRD, SEM, UV-DRS, TEM, and TGA/DTG are used to characterize different concentrations of Zn-ZIF. Zn-ZIF's crystalline structure and phase purity have been verified by PXRD. Using diffuse reflectance spectra, the Kubelka-Monk function determined the band gaps of the Zn-ZIF samples, and scanning electron microscopy revealed a more porous structure. At 77 K and 1 bar, the Zn-ZIF solution with a 2:1 ratio had the highest hydrogen storage capacity (1.71 wt%). The electrochemical behavior of several Zn-ZIF electrodes in a 6 M KOH electrolyte was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments. The Zn-ZIF electrode with a 2:1 ratio exhibits a low charge transfer resistance and a high proton diffusion coefficient (D) of 1.687 × 10−4 cm2 s−1. The characteristics of the 2:1 synthesized Zn-ZIF electrode as a supercapacitor were investigated. Our analysis of the generated Zn-ZIF material's specific capacitance values after 2000 cycles revealed an impressive retention rate of nearly 89 %, with values of 296.6 Fg-1. In addition, we examined the photocatalytic activities of the as-synthesized material by exposing it to ultraviolet light and seeing how it degraded organic dyes such as Cango-Red (CR) dye. With a photocatalytic efficacy of 95.06 % for CR dye, Zn-ZIF (2:1 ratio) is the most effective. These findings should provide new knowledge for researchers interested in developing novel Zn-ZIF materials for photocatalytic, energy storage, and hydrogen storage applications.

Tailoring Sb-F doped ZnO nanoparticles for dual-functionality: Photocatalytic and supercapacitor applications

In the present work, pure zinc oxide nanoparticles (ZnO NPs), antimony doped ZnO nanoparticles (Sb-ZnO NPs), fluorine doped ZnO nanoparticles (F-ZnO NPs), and antimony and fluorine co-doped ZnO nanoparticles (Sb/F-ZnO NPs) with various dopant concentrations are synthesized by co-precipitation method. The optical, structural, morphological, photocatalytic, and electrochemical activities of ZnO nanostructures by the influence of Sb and F doping were investigated. XRD showed crystallite size decreased with increasing Sb/F content, while BET showed 64.25 m2/g surface area for ZnO-5 %Sb-10 %F. SEM and TEM images suggesting Sb/F doping changed the ZnO morphology from spherical to bricks-built and nanorod-built flower structures. XPS verified Sb (+3) and F (−1) oxidation states, while absorption spectroscopy showed increased energy bandgap with 5 % Sb and 10 % F doping in ZnO. The photocatalytic activity for mixture of congo red, rhodamine B, and methylene blue are closer to real polluted water. All the samples exhibited good photocatalytic activity for the methylene blue with degradation efficiency reaching to 99 %. At a constant current density of 1 A/g, symmetric supercapacitors utilizing Sb/F-ZnO electrodes exhibited a specific capacitance of 762 Fg−1, underscoring their superior electrochemical performance and potential for advancing energy storage technologies. Further, physiochemical and electrochemical properties of ZnO can be perfectly tuned by the optimal setting for co-doping in ZnO up to 5 % Sb and 10 % F by the co-precipitation approach.

Moisture-Stable CsSnBr2Cl Halide Perovskite: Electrochemical Insights in Aqueous Environments.

In this investigation, moisture-stable CsSnBr2Cl nanoparticles were synthesized by incorporating Cl into CsSnBr3 halide perovskite using the hot injection method. Various analyses including XRD, XPS, UV-vis absorbance, photoluminescence, and Mott-Schottky have confirmed that the structural properties, chemical states, optical properties, and electronic band structure of CsSnBr2Cl nanoparticles remain intact even after 75 days of water immersion, thereby conclusively demonstrating their moisture stability. In a three-electrode system, the comparative electrochemical performance of pristine CsSnBr3 nanoparticles and moisture-stable Cl-incorporated CsSnBr2Cl nanoparticles was evaluated in various aqueous electrolytes, including HCl, Na2SO4, and KOH. The results indicate that the CsSnBr2Cl electrode material exhibits superior electrochemical properties, such as a larger integrated cyclic voltammetry (CV) area, a wider potential window, longer charge-discharge times, and lower impedance parameters compared to the pristine CsSnBr3 nanoparticles. The electrochemical performance of CsSnBr2Cl nanoparticles was evaluated for potential applications in batteries, supercapacitors, fuel cells, and water splitting, with a focus on reaction kinetics, charge storage mechanisms, and impedance parameters. The electrochemical properties of the nanoparticles were assessed using a three-electrode configuration across various 0.5 M aqueous electrolytes (HCl, Na2SO4, and KOH). In HCl, the nanoparticles demonstrated impressive charge storage capability, achieving a capacitance of 474 F g-1 at 1 A g-1, affirming their suitability for energy storage devices. In Na2SO4(aq.), the nanoparticles exhibited excellent stability for supercapacitors, operating up to 1.6 V without significant oxygen evolution. Notably, in KOH, they demonstrated potential as effective water-splitting electrodes. The practical applicability of the nanoparticles was evaluated using a symmetric two-electrode configuration with HCl and Na2SO4 electrolytes. The capacitance values were 117 F g-1 in HCl and 70 F g-1 in Na2SO4 at 1 A g-1. Notably, after 5000 GCD cycles in HCl(aq.), the nanoparticles retained 93% of their capacitance and maintained 91% Coulombic efficiency. They also demonstrated stable operation across a temperature range of 3 to 60 °C, achieving an energy density of 5.83 W h kg-1 at a power density of 600 W kg-1. This study emphasizes the considerable potential of CsSnBr2Cl nanoparticles in advancing electrochemical energy storage technologies and sets a solid foundation for future research and development in metal halide perovskites.

Small scale pool fires: The case of toluene

Industrial applications adopting toluene as a solvent have been largely extended in recent years, including solutions within the framework of the energy transition and energy storage technologies. The potential use of this flammable compound in a different set of operative conditions and compositions requires a comprehensive and complete knowledge of its fire behaviour and combustion kinetic. To this scope, an innovative experimental procedure applicable to liquid reactive systems was developed for this scope and implemented at different boundary conditions. More specifically, the specimen was exposed to air and heat fluxes between 7 and 50 kW/m2, at a constant sample surface of 0.01 m2, an initial sample thickness of 0.01 m, and a distance between the sample and the horizontally oriented conical-shaped heater of 0.025 m. Measurements were compared with data from the current literature, when available, demonstrating the robustness and validity of the adopted procedure. Although an increase in the external flux leads to growing mass burning rates (i.e., from 0.47 g/s to 0.85 g/s), negligible effects on the ignitability were observed. Conversely, a peak in the heat release rate at 35 kW/m2 was measured. The observed reduction at higher external heat fluxes was attributed to less effective combustion, demonstrating that the maximum expected heat flux cannot be considered as an aprioristic worst-case scenario for the evaluation of pool fires. The collected data were, then, further utilized to obtain insights on the formation of the main products, including soot tendency. Based on the collected data a simplified kinetic model suitable for the computational fluid dynamics was proposed to reproduce the chemistry of the system.

Surface Gradient Desodiation Chemistry in Layered Oxide Cathode Materials.

Sodium-ion batteries (SIBs) as a promising technology for large-scale energy storage have received unprecedented attention. However, the cathodes in SIBs generally suffer from detrimental cathode-electrolyte interfacial side reactions and structural degradation during cycling, which leads to severe capacity fade and voltage decay. Here, we have developed an ultra-stable Na0.72Ni0.20Co0.21Mn0.55Mg0.036O2 (NCM-CS-GMg) cathode material in which a Mg-free core is encapsulated by a shell with gradient distribution of Mg using coprecipitation method with Mg-hysteretic cascade feedstock followed by calcination. From the interior to outer surface of the shell, as the content of electrochemically inactive Mg gradually increases, the Na+ deintercalation amount gradually decreases after charged. Benefiting from this surface gradient desodiation, the surface transition metal (TM) ion migration from TM layers to Na layers is effectively inhibited, thus suppressing the layered-to-rock-salt phase transition and the resultant microcracks. Besides, the less formation of high-valence TM ions on the surface contributes to a stable cathode-electrolyte interface. The as-prepared NCM-CS-GMg exhibits remarkable cycling life over 3000 cycles with a negligible voltage drop (0.127 mV per cycle). Our findings highlight an effective way to developing sustainable cathode materials without compromising on the initial specific capacity for SIBs.

Development Overview and Perspective of Semi‐Solid Flow Batteries

The development of efficient and cost‐effective grid energy storage devices is crucial for advancing the future of renewable energy. Semi‐solid flow batteries, as an emerging energy storage technology, offer significantly higher energy density and lower costs compared to traditional liquid flow batteries. However, the complex interplay between rheology and electrochemistry poses challenges for in‐depth investigation. With a sketch of historical development of semi‐solid flow batteries, this minireview summarizes several key issues, including particle interactions, electron transport, and the sustainability of electrochemical reactions in slurry electrodes. By tracing the technological evolution of semi‐solid flow batteries, we provide a forward‐looking perspective on their potential application in future large‐scale energy storage systems, highlighting their promising role in addressing the challenges of energy transition.

Thin, Uniform, and Highly Packed Multifunctional Structural Carbon Fiber Composite Battery Lamina Informed by Solid Polymer Electrolyte Cure Kinetics.

Multifunctional structural batteries promise advancements in structural energy storage technologies by seamlessly integrating load-bearing and energy-storage functions within a single material, reducing weight, and enhancing safety. Yet, commercialization faces challenges in materials processing, assembly, and design optimization. Here, we report a systematic approach to develop a carbon fiber (CF)-based structural battery impregnated with epoxy-based solid polymer electrolyte (SPE) via robust vacuum-assisted compression molding (VACM). Informed by cure kinetics, SPE processing enhances the multifunctional performance with no fillers or additives. The thin flexible CF-based laminae impregnated under high pressure achieved a substantial enhancement of ∼160% in the fiber volume fraction (FVF) as although thin and strip-shaped, the fibers were optimally packed with low void. A CF/SPE-based battery was fabricated, with a hybrid layered ionic liquid (IL)/ carbonate electrolyte (CE) showing enhanced safety and multifunctional performance. Enhanced by thin, uniform, and stiff CF-based composites, this study propels the development of advanced multifunctional structures, thereby expediting sustainable commercialization.

Pd2+-coordinated polybenzimidazole membranes with fast and selective ion transport for alkaline aqueous organic redox flow battery

The advancement of aqueous organic redox-flow batteries (AORFBs) is impeded by the lack of efficient, low-resistance, and highly selective ion-conducting membranes (ICMs). Although polybenzimidazole (PBI) is one of the most promising low-cost non-fluorinated ion-conducting membranes, it remains challenging to design stable PBI membranes with fast and selective ion transport channels. Here, we engineer the chemical structure of PBI and regulate the ion transport channels to prepare highly conductive and selective Pd2+-coordinated membranes with grafting and crosslinking structures. In this design, the positively charged quaternary ammonium groups on the side chain improve the conductivity of OH−, while the continuous cross-linked network formed by ionic bonds between quaternary ammonium groups and deprotonated imidazole groups significantly enhances the membrane's mechanical properties. Furthermore, the coordination of Pd2+ with PBI and plasticization of PBI chain by trifluoroacetate anions expand the molecular free volume while inducing local contraction. Consequently, the QPBI-xPBI-Pd membrane enables fast charge carrier transport and suppresses the diffusion of active substances. The AORFBs assembled with the QPBI-10PBI-Pd membranes exhibit high coulombic efficiency (99.6 %) and energy efficiency (77.67 %) at 100 mA cm−2, maintaining excellent stability for 500 cycles. This study provides an innovative strategy to design high-performance PBI membranes for RFBs, thereby advancing the viability of RFBs in the realm of large-scale energy storage technologies.

Dissolution Manufacturing Strategy for the Facile Synthesis of Nanoporous Metallic Glass Multifunctional Catalyst.

The quest for heightened energy efficiency is inextricably linked to advancements in energy storage and conversion technologies, wherein multifunctional catalysts play a pivotal role by mitigating the slow kinetics endemic to many catalytic reactions. The intricate synthesis and bespoke design of such catalysts, however, present notable challenges. Addressing this, the present study capitalizes on a novel dissolution manufacturing strategy to engineer self-supporting, nanoporous multifunctional electrocatalysts, circumventing the prevalent issue of customizing catalytic functionalities upon demand. This innovative approach grants the flexibility to finely tune the incorporation of active species and metalloid binders, culminating in the creation of a self-supporting nanoporous metal glass electrocatalyst doped with RuO2 (NPMG@RuO2) with outstanding performance in alkaline media. The catalyst showcases superior electrocatalytic activity, achieving low overpotentials of 41.50 mV for the Hydrogen Evolution Reaction and 226.0 mV for Oxygen Evolution Reaction alongside sustained stability over 620 hours.These achievements are attributed to the distinct nanoporous architecture that ensures a high density of catalytic sites and mechanical strength, bolstered by the synergistic interplay between RuO2 and Pt-based metallic glass. The findings provide a versatile template for the development of nanoporous multifunctional catalysts, signifying a leap forward in the realm of energy conversion technologies.

A theoretical perspective on solid-state ionic interfaces.

Solid-state ionic conductors find application across various domains in materials science, particularly showcasing their significance in energy storage and conversion technologies. To effectively utilize these materials in high-performance electrochemical devices, a comprehensive understanding and precise control of charge carriers' distribution and ionic mobility at interfaces are paramount. A major challenge lies in unravelling the atomic-level processes governing ion dynamics within intricate solid and interfacial structures, such as grain boundaries and heterophases. From a theoretical viewpoint, in this Perspective article, my focus is to offer an overview of the current comprehension of key aspects related to solid-state ionic interfaces, with a particular emphasis on solid electrolytes for batteries, while providing a personal critical assessment of recent research advancements. I begin by introducing fundamental concepts for understanding solid-state conductors, such as the classical diffusion model and chemical potential. Subsequently, I delve into the modelling of space-charge regions, which are pivotal for understanding the physicochemical origins of charge redistribution at electrified interfaces. Finally, I discuss modern computational methods, such as density functional theory and machine-learned potentials, which offer invaluable tools for gaining insights into the atomic-scale behaviour of solid-state ionic interfaces, including both ionic mobility and interfacial reactivity aspects. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Emerging Two-Dimensional Materials for Proton-Based Energy Storage.

The rapid diffusion kinetics and smallest ion radius make protons the ideal cations toward the ultimate energy storage technology combining the ultrafast charging capabilities of supercapacitors and the high energy densities of batteries. Despite the concept existing for centuries, the lack of satisfactory electrode materials hinders its practical development. Recently, the rapid advancement of the emerging two-dimensional (2D) materials, characterized by their ultrathin morphology, interlayer van der Waals gaps, and distinctive electrochemical properties, injects promises into future proton-based energy storage systems. In this perspective, we comprehensively summarize the current advances in proton-based energy storage based on 2D materials. We begin by providing an overview of proton-based energy storage systems, including proton batteries, pseudocapacitors and electrical double layer capacitors. We then elucidate the fundamental knowledge about proton transport characteristics, including in electrolytes, at electrolyte/electrode interfaces, and within electrode materials, particularly in 2D material systems. We comprehensively summarize specific cases of 2D materials as proton electrodes, detailing their design concepts, proton transport mechanism and electrochemical performance. Finally, we provide insights into the prospects of proton-based energy storage systems, emphasizing the importance of rational design of 2D electrode materials and matching electrolyte systems.

Emerging Capacitive Materials for On-Chip Electronics Energy Storage Technologies

Miniaturized energy storage devices, such as electrostatic nanocapacitors and electrochemical micro-supercapacitors (MSCs), are important components in on-chip energy supply systems, facilitating the development of autonomous microelectronic devices with enhanced performance and efficiency. The performance of the on-chip energy storage devices heavily relies on the electrode materials, necessitating continuous advancements in material design and synthesis. This review provides an overview of recent developments in electrode materials for on-chip MSCs and electrostatic (micro-/nano-) capacitors, focusing on enhancing energy density, power density, and device stability. The review begins by discussing the fundamental requirements for electrode materials in MSCs, including high specific surface area, good conductivity, and excellent electrochemical stability. Subsequently, various categories of electrode materials are evaluated in terms of their charge storage mechanisms, electrochemical performance, and compatibility with on-chip fabrication processes. Furthermore, recent strategies to enhance the performance of electrode materials are discussed, including nanostructuring, doping, heteroatom incorporation, hybridization with other capacitive materials, and electrode configurations.

Maturity assessment of grid-scale flexibility and energy storage services towards a decarbonized Europe

Background The study evaluates the maturity of grid-scale flexibility services, essential for Europe's transition to a decarbonized economy. Conducted under the Horizon-Europe SINNOGENES project, it focuses on energy storage technologies, regulatory frameworks, and stakeholder perspectives. Methods The methodology comprises three phases. First, significant grid-scale energy storage and flexibility technologies, including Battery Energy Storage Systems (BESS) and Vehicle-to-Grid (V2G) systems, were reviewed. Second, the regulatory framework for flexibility services at the EU transmission systems level was assessed, analyzing key EU directives and national regulations from Spain, Portugal, Germany, Cyprus, and Switzerland. Third, stakeholder perspectives were gathered through a survey of forty-four stakeholders in the European energy sector and bilateral interviews with companies and organizations in the energy sector. Results Technological advancements in grid-scale flexibility services have been identified, along with persistent regulatory challenges. The survey and interviews revealed a varied perception among stakeholders regarding the maturity and implementation of these services. A high demand for flexibility was noted, with 77% of stakeholders expressing a need for or active use of flexibility services. Electrochemical energy storage and demand response were highlighted as the most relevant technologies. However, high implementation costs, perceived insufficient benefits, and regulatory uncertainties were major barriers to widespread adoption. Conclusions The study concludes that despite notable technological progress and some regulatory advancements, several barriers still impede the full maturity and integration of grid-scale flexibility services in Europe. Addressing these regulatory and market challenges is crucial for achieving a fully functional and integrated flexibility service framework across the European grid. Harmonized regulations, financial incentives, and clear long-term pricing signals are essential to support the market.