Vanadium flow batteries (VFBs) are promising for grid-scale, long-duration energy storage, but their long-term operation is limited by capacity decay from electrolyte imbalance, especially oxidative valence drift caused by parasitic side reactions. Here, we report an inline capacity recovery strategy based on methanol-mediated catalytic rebalancing during VFB operation. As a compact chemical electron carrier, methanol delivers 6 electrons per molecule upon full oxidation, providing high gravimetric electron density and low materials cost. A methanol-fed Pt/C side-stream reactor was integrated with the VFB posolyte loop to reduce excess VO 2 + and rebalance the electrolyte valence. Spectroscopic analyses confirm quantitative conversion without detectable residual methanol-derived organic species under the testing conditions. An inline recovery was triggered whenever capacity retention decreased to ~95%, repeatedly restoring the capacity to >99% of its initial value during 30 days of continuous operation. This strategy provides a practical route for continuous VFB capacity maintenance and electrolyte lifecycle management.

Widespread deployment of hydrogen energy is limited by the safety risks and energy penalties of compressed and liquefied storage, whereas alternative hydrogen carriers often require harsh operating conditions or exhibit sluggish kinetics. Here we report a redox-mediated flow cell architecture based on solid organic hydrogen carriers (SOHCs) that enables reversible hydrogen storage and release at ambient temperature and pressure. The system is driven by the rapid, reversible interconversion between hydrogen and proton-electron pairs via the hydrogen oxidation and evolution reactions, while soluble redox mediators shuttle protons and electrons between the electrode and a separate tank containing the solid carrier. This dual-mediator proton-coupled electron transfer (PCET) strategy enables rapid charging and discharging under ambient conditions while decoupling electrochemical hydrogen conversion from hydrogen storage. Using this approach, we achieve a volumetric hydrogen storage density equivalent to approximately 120 bar compressed gas without pressurized vessels. These results open a route that combines the high power density of flow cells with the high energy density of solid-phase materials and provides a scalable, safe, and efficient pathway for stationary hydrogen storage. The modularity in this approach provides a general platform in which the solid carrier, redox mediators, and flow-cell operation can be optimized independently, creating pathways to higher storage density, lower voltage hysteresis, improved kinetics, and broader materials compatibility beyond the specific substances demonstrated here, e.g., including inorganic materials exhibiting a PCET mechanism.

Redox-mediated reactions enable charge transfer processes beyond conventional heterogeneous electrode interfaces and have emerged as versatile strategies in energy storage and conversion systems. However, the interfacial electron transfer mechanisms governing these reactions remain elusive. Here, ferrocene derivatives are employed as redox mediators to investigate interfacial electron transfer using the FePO4/LiFePO4 intercalation reaction as a model system, enabling independent control of thermodynamic driving force and electron transfer distance. This approach allows direct experimental observation of a Marcus-type inverted region. More importantly, the dependence of reaction kinetics on driving force can be fundamentally altered by interfacial electronic coupling, such that electron transfer distance becomes a dominant factor governing the overall reaction rate. Molecular stability further emerges as a key factor governing the effectiveness of redox-mediated processes under practical conditions and high utilization of FePO4 (up to 97%) is achieved through rational mediator selection. These results provide a general framework for understanding interfacial electron transfer in complex electrochemical environments and reveal the key factors governing redox-mediated reactions.

In tandem with the global push for carbon neutrality, many countries have begun mass adoption of electric vehicles (EVs) to reduce carbon emissions. Such measures have driven an unprecedented demand for battery raw materials, such as nickel, which exacerbates pollution woes for countries producing such materials. Indonesia, the largest supplier of nickel in the world, extracts nickel from laterite ores using high-pressure acid leaching (HPAL) and outputs mixed nickel-cobalt precipitates for battery applications. Unfortunately, HPAL generates significant quantities of hazardous liquid tailings annually, up to 1.6 tonnes of waste tailings would be generated for every tonne of nickel, resulting in severe environmental problems. Here, we introduce a decoupled mediated electrodialysis (DMED) method for acid-base generation that enables a circular nickel laterite extraction process. Unlike conventional electrolytic electrodialysis (EED) which suffers from low product concentrations and high energy consumption due to proton leakage, and bipolar membrane electrodialysis (BMED) which is constrained by complex membrane chemistry, high material costs and sophisticated stack architecture, DMED circumvents the challenges of both methods by introducing a redox mediator to decouple the acid and base generation process. This fundamentally prevents the leakage of protons, enabling the production of exceptionally high H + (8.9 M) and OH - (5.0 M) concentrations. High current efficiencies (>80 %) was maintained during stability tests under 80 mA cm -2 on par with state-of-the-art systems. The incorporation of DMED to nickel laterite extraction would greatly reduce chemical consumption and hazardous waste discharge, transforming a traditionally linear operation into a circular one.

Electrified generation of acids and bases from saline waste streams is essential for sustainable waste utilization and crucial to building a circular ecosystem. Existing salt splitting technologies, such as electrolytic electrodialysis (EED) and bipolar membrane electrodialysis (BMED) are hindered by proton leakage, high energy consumption and complex multi-stack architecture. Here, we introduce a decoupled mediated electrodialysis (DMED) method for acid-base generation that fundamentally prevents proton leakage and improves energy consumption. By introducing a redox mediator to decouple the acid and base generation process, an unprecedentedly high concentration of H + (8.90 M) and OH - (5.20 M) can be generated. High current efficiencies (> 85%) for both acid and base generation could be achieved even at a current density of 100 mA cm -2 . We further demonstrate DMED in nickel laterite extraction, where acid and base are heavily used for leaching and precipitation. DMED electrochemically regenerates the consumed H 2 SO 4 and NaOH from the residual solution to enable a fully electrified closed-loop extraction process. Such integration greatly reduces chemical consumption and hazardous waste discharge, transforming a traditionally linear operation into a circular one. Beyond mining, this platform offers a scalable and energy-efficient route to electrify acid-base production from diverse saline waste sources, opening new possibilities for sustainable manufacturing and efficient resource recovery

Conventional crystalline-on-crystalline anti-chloride overlayer structures for seawater oxidation electrocatalysis suffer from physical shielding of active sites and limited functional tunability due to lattice constraints. Herein, a crystalline-amorphous CoS2-MnOx heterostructure is constructed on graphite felt via a sequential electrodeposition-hydrothermal route, with deposition order mediating precise interface regulation. The as-prepared structure exhibits superior electrocatalytic performance for alkaline seawater oxidation, demanding low overpotentials of 170, 308, and 392 mV to achieve current densities of 10, 100, and 500 mA cm−2, respectively, together with robust stability. Experimental investigation and theoretical calculation reveal that the heterostructure triggers electron transfer from MnOx to CoS2, generating a built-in electric field with interfacial charge redistribution. This modulates the d-band center and accelerates oxygen evolution kinetics. Meanwhile, surface electron enrichment synergizes with released manganate ions to effectively repel chloride ions from approaching and adsorbing. Such directional electron and ion fluxes endow the catalyst with excellent chloride-resisting and oxygen evolution performances in seawater electrolysis. This work demonstrates a facile strategy for constructing crystalline-amorphous heterostructures and elucidates the interfacial engineering mechanism for enhanced seawater oxidation, offering a promising new paradigm for advanced electrocatalysts in green hydrogen industry.

Aqueous proton-coupled energy storage systems enable ultrafast charging and intrinsic safety in aqueous electrolytes, but the durable anodes operating at low potential (<0.3 V vs SHE) in acidic conditions are still challenging. This work introduces 1,6-poly(phenazine sulfide) (1,6-PPS), a functionally sulfur-bridged phenazine polymer anode designed to overcome key challenges. Its minimalist architecture enables exceptional stability in 1 M H2SO4, exhibiting near-zero capacity decay over 10,000 cycles. 1,6-PPS also delivers ultrafast kinetics, retaining 56% of theoretical capacity (141 mAh g(-1)) at 50 A g(-1) due to extended pi-conjugation and high proton diffusivity (5 x 10(-7) to 10(-9) cm(2) s(-1)). The synthesis maximizes redox-active phenazine density, achieving a high specific capacity of 255 mAh g(-1). In a full cell with a N,N '-(2,5-dichloro-1,4-phenylene)bis(butane-1-sulfonamide) cathode, 1,6-PPS demonstrates a stable 0.77 V output and 96.4% capacity retention over 500 cycles. This work establishes sulfur-bridged phenazine polymers as durable, high-performance anodes for next-generation proton batteries.

Organic framework cathodes are promising for high-current lithium-ion batteries (LIBs) owing to their tunable porosity and abundant redox-active sites, yet their intrinsic lithium-free nature hinders practical coupling with commercial carbon anodes and necessitates effective pre-lithiation. Herein, we propose a potential-controlled strategy employing a fixed-potential mediator to enable rapid and precise pre-lithiation of organic frameworks. Demonstrating this with CuHHTP and LTO as the mediator, the pre-lithiated Li-CuHHTP retains structural integrity while exhibiting pseudocapacitance-dominated charge storage, superior electronic conductivity, and fast Li-ion diffusion. Consequently, it delivers 83.6 mAh·g−1 capacity at an ultra-high current of 60 A·g−1. The Li-CuHHTP also exhibits full compatibility with lithium-free hard carbon anodes, achieving 32.2 mAh·g−1 at 30 A·g−1 and retaining 82.8 mAh·g−1 with 87.4% capacity retention after 5,000 cycles at 3.0 A·g−1. By enabling well-regulated lithium insertion, coupled with structural integrity and electrochemical properties preserved, this strategy unlocks organic frameworks’ potential as kinetically capable cathodes for high current LIBs.

ABSTRACT Solar rechargeable flow batteries (SRFBs), which integrate solar energy conversion with electrochemical energy storage, have attracted increasing attention in recent years. To date, the reported photoelectrode‐based SRFBs predominantly employ either a single photoanode or a photoanode coupled with a silicon‐based photocathode for battery charging. Although silicon possesses an optimal bandgap and outstanding light‐harvesting capability, its intrinsic instability in aqueous environments and severe interfacial charge recombination necessitate complex and precisely engineered device architectures, thereby fundamentally limiting its scalability and practical deployment. Consequently, metal‐oxide photoelectrodes emerge as more viable candidates for SRFB applications. Herein, we report for the first time an SRFB architecture incorporating a Cu 2 O photocathode in conjunction with an iron‐oxide photoanode and the Fe(BPMG) 2 (II)/Fe(BPMG) 2 (III) and Fe 2+ /Fe 3+ redox couples. Benefiting from rational photoelectrode and interface design, the Cu 2 O photocathode delivers an applied‐bias photon‐to‐current efficiency (ABPE) of up to 0.48%. As a result, the assembled SRFB achieves an output voltage of 0.62 V and a solar‐to‐output electricity efficiency of approximately 0.11%. This work demonstrates the feasibility of employing metal‐oxide photocathodes in SRFB systems and provides a new design paradigm for the development of advanced photocathodes toward fully solar‐driven flow battery technologies.

The development of high-capacity organic electrodes for aqueous proton batteries is hindered by incomplete redox activity and structural instability. Here, we report a methyl-functionalized phenazine derivative, 2,3,8,9,14,15-hexamethyl-5,6,11,12,17,18-hexaazatrinaphthalene (HMHATN), engineered to synergize electronic delocalization and steric control. Methyl groups at peripheral positions electronically stabilize the intermediate redox states via charge redistribution, lowering the redox potential to 0.23 V vs SHE and enabling a six-electron transfer process. Sterically, methylation induces a herringbone molecular packing, shortening nitrogen-to-nitrogen distances by 9% and creating dual proton transport pathways: a Grotthuss-type hopping network via optimized hydrogen bonds and a vehicle-type highway for protons, as validated by AIMD simulations. These structural and electronic modifications suppress aggregation-induced passivation with a limited electron transfer number observed in nonmethylated analogues, unlocking full redox reversibility. HMHATN delivers a near-theoretical capacity (298 mAh/g at 1 A/g), exceptional rate capability (226 mAh/g at 50 A/g), and ultralong cyclability (85.9% retention over 10,000 cycles). Full-cell configurations with a CuHCF cathode further demonstrate practical viability, achieving 276 mAh/g at 2 A/g with 92.7% capacity retention over 3000 cycles. This work is anticipated to establish a universal way of designing organic electrodes, where targeted functionalization harmonizes electronic and steric effects to overcome limitations in proton-coupled energy storage.

The practical application of lithium metal batteries (LMBs) requires electrolytes that simultaneously ensure high safety and interfacial stability. Although locally concentrated ionic liquid electrolytes (LCILEs) exhibit exceptional electrochemical stability and compatibility with electrode electrolyte interfaces (EEIs), two major challenges persist: (i) safety risks caused by excessive low-flash-point diluents, and (ii) insufficient understanding of how diluents modulate solvation structures. Herein, we introduce a low-diluent-content LCILE system composed of lithium bis(fluorosulfonyl)imide (LiFSI) salt, Nmethyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI) ionic liquid, and trifluoromethanesulfonate (TFS) diluent. The TFS diluent strengthens ion-ion interactions by lowering the dielectric constant of the electrolyte, resulting in the formation of a unique nanometric anion aggregates (N-AGGs) reinforced solvation structure. These large anionic clusters exhibit accelerated redox decomposition kinetics, facilitating the rapid formation of a thin, dense, and low-impedance EEI. Consequently, the Li/ LiNi0.6Co0.2Mn0.2O2 coin cell achieves 87.8 % capacity retention over 300 cycles at 4.3 V, while a practical 1.4 Ah Li/NCM622 pouch cell retains 84.5 % capacity after 80 cycles at 4.5 V. Furthermore, the electrolyte demonstrates exceptional safety, and 2 Ah Li metal pouch cells successfully pass rigorous nail penetration tests without any ignition or explosion. This work not only provides a design strategy for intrinsically safe and high-performance electrolytes but also highlights the critical role of anion cluster decomposition kinetics in shaping EEI formation. (c) 2025 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

After 30 years of commercialization and mass production, a myriad of lithium-ion batteries have been produced. It has generated a massive amount of battery waste after the batteries reach their lifetime. This would be more so with the widespread applications of lithium-ion batteries for electric vehicles. For sustainable development, it has never been so pressing to recycle the spent batteries and valorize the useful components. However, the commonly used pyrometallurgical and hydrometallurgical methods are either energy-intensive or consume large amounts of chemicals. Here, using LiCoO 2 as an example, we report a closed-loop electrified chemical process based on redox-targeting reactions to recover valuable species from spent battery materials using only electricity and water. Complimentary reductive leaching of LiCoO 2 and oxidative leaching of LiFePO 4 were performed with anthraquinone-2,7-disulfonate as a regenerative redox mediator to sequentially break down LiCoO 2 and achieve efficient separation of Co 2+ and Li + in the form of Co(OH) 2 and LiOH. This cost-effective and environmentally friendly method was also extended to the recycling of LiNi x Mn y Co z O 2 with a high recovery rate of Li+ and transition metal species. It is anticipated that the electrified chemical recycling method demonstrated here would provide a credible solution to the valorization of battery waste and contribute to the sustainable development of lithium-ion batteries.

A growing share of variable renewable generation requires low-cost, long-duration grid-level energy storage. Aqueous organic redox flow batteries (AORFBs) offer tunable molecular chemistry and scalable flow architecture; acidic systems enable high power and leverage mature vanadium-flow hardware. A central challenge is designing posolytes that combine high redox potential, solubility, capacity density, and stability. Here, we report a two-electron azo-based zwitterionic molecule 4,4'-azo-bis(1-pyridinium-3-propane-sulfonate) (ABPS) that addresses these constraints through intrinsic structural features. The zwitterionic character dramatically enhances water solubility (1.30 M in 2.0 M H2SO4) while maintaining overall electroneutrality, thereby intrinsically reducing molecule crossover and suppressing capacity decay during cycling. Symmetric cell testing confirms outstanding stability over 3800 cycles (∼100 days) with an average coulombic efficiency (CE) of 99.98% and nearly zero capacity loss (0.198% year-1). In the full cell demonstration, ABPS delivers a high voltage of 1.14 V (paired with V2+/3+). A capacity density of 48.5 Ah L-1 and the corresponding posolyte energy density of 55.3 Wh L-1 are achieved (1.0 M molecule concentration), and an ultralow capacity decay rate of 0.084% year-1 over 1100 h of operation. The rational design of azo-based zwitterionic structure thus offers a promising universal route to durable, high-power acidic AORFB posolytes.

Redox-targeting flow batteries (RTFBs) offer a way to boost the energy density of traditional flow batteries. In RTFBs, solid materials need to be mixed with binders to form granules, and the utilization of these solid materials hinges on the granule's preparation method. However, so far, this preparation method has not been well-designed, preventing the full realization of RTFBs' high-energy-density potential. This study presents a phase-inversion granulation approach to create high-porosity and high-tortuosity granules for RTFBs. Spherical granules made by this method had a porosity of 69.44%. As a result, the utilization of LiFePO4 granules in RTFBs is increased to over 99.5%, the highest reported value. CT and FIB-SEM characterizations were used to clarify the 3D model of the porous granules. Furthermore, a zinc-based RTFB with LiFePO4 granules in the cathodic tank achieved an energy density of 122.1 Wh/L and a capacity retention rate of over 94% of its initial capacity after 140 h of continuous charge-discharge. This research offers a strategy for fabricating high-utilization granules for RTFBs.

The integration of solar energy into redox-flow batteries (RFBs) has recently attracted considerable attention as a promising strategy for sustainable energy storage. However, most early efforts have simply combined conventional photovoltaic cells with flow batteries, without achieving true functional coupling or synergistic operation between the two systems. This limitation is especially pronounced in high-voltage RFBs, where the photovoltaic component must deliver equally high photovoltages, often leading to complicated configurations and elevated fabrication costs. In this study, we present a simple and cost-effective approach by developing an all-iron photo-assisted redox-flow battery (PARFB) that integrates an iron oxide photoanode with K4[Fe(CN)6]/K3[Fe(CN)6] and FeTiPA(II)/FeTiPA(III) as the redox couples. By optimizing the interfacial charge-transfer kinetics at the electrode level, the system achieves a 15% reduction in charging energy, an output voltage of ~1.20 V, and a solar-to-output energy conversion efficiency of 0.1%, which is comparable to previously reported hematite-based photoelectrode systems. This work offers a viable and scalable strategy for coupling solar energy harvesting with redox-flow battery technologies, particularly for systems requiring high operational voltages.

Chemically stable interfaces in electrodes are indispensable for maintaining the robust electrochemical interphase evolution to ensure long-term cycling stability of lithium-ion batteries. However, the potential impact on interfacial chemistry by residual protons in association with carboxyl and hydroxyl groups in water-soluble binders (e.g., PAA, CMC/SBR), which are inevitably introduced during the slurry-casting fabrication of electrodes, has received limited attention. Herein, we uncover that the chemically reactive protons trigger ethylene carbonate ring-opening reactions, thereby disrupting the solid electrolyte interphase (SEI) formation and stability, ultimately degrading battery performance. Building on this new insight, a chemically stable, deprotonated electrode (DE) featuring much reinforced interfaces arising from heterogeneous carbon-oxygen covalent bonds is developed, which enables stronger chemical anchoring than the hydrogen bond interactions by carboxyl and hydroxyl groups. In addition, the thus-developed oxygen-rich deprotonated interface reshapes the formation of an inner Li2O-dominated SEI. This deprotonation approach demonstrates broad compatibility with several anode active materials, including microsized SiO, Si, graphite, and their composites. For example, DEs with 86 wt·% SiO/graphite and 80 wt·% 5 μm-sized Si deliver 5.14 mAh·cm-2 over 500 cycles and 4.32 mAh·cm-2 over 200 cycles, respectively. With the new DEs, two Ah-level cells paired with LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.2 cathodes achieve the respective gravimetric energy densities of 288 Wh·kg-1 and 424 Wh·kg-1, while maintaining the capacity retention of 81% over 300 and 78% over 600 cycles. The present work reveals the deprotonation-driven interphase stability mechanism and establishes active-component regulation as a new paradigm for high-energy density lithium-ion batteries.

After 30 years of commercialization and mass production, lithium-ion batteries have generated massive waste streams, especially with their expanding use in electric vehicles. Recycling spent batteries and valorizing useful components are therefore increasingly urgent for sustainable development. However, conventional pyrometallurgical and hydrometallurgical methods are limited by high energy consumption or large chemical input, creating demand for greener and more efficient recycling technologies. Here, using LiCoO 2 as an example, we report a closed-loop electrified chemical process based on redox-targeting reactions to recover valuable species from spent battery materials using only electricity and water. Complimentary reductive leaching of LiCoO 2 and oxidative leaching of LiFePO 4 were performed with anthraquinone-2,7-disulfonate as a regenerative redox mediator to sequentially break down LiCoO 2 and achieve efficient separation of Co 2+ and Li + in the form of Co(OH) 2 and LiOH. This cost-effective and environmentally friendly method was also extended to the recycling of LiNi x Mn y Co z O 2 with a high recovery rate of Li+ and transition metal species. It is anticipated that the electrified chemical recycling method demonstrated here would provide a credible solution to the valorization of battery waste and contribute to the sustainable development of lithium-ion batteries.

Neutral zinc-iron flow batteries (ZIFBs) are promising candidates for grid-scale energy storage due to their safety, low cost, and sustainability. However, their cycle stability and energy density are restricted by zinc dendrite growth, hydrogen evolution, and more positive Zn anode potential in neutral media compared to alkaline conditions. Herein, we propose a ligand-coordination strategy using tetrasodium iminodisuccinate (IDs) to rationally tune the redox behavior of Zn2+. The formation of a stable [H4Zn(C8H7NO8)2]2- complex converts the conversional Zn(H2O)6 2+ structure into a chelate-dominated configuration, inducing an outer-sphere electron transfer pathway by preventing direct Zn-electrode interactions. Meanwhile, it results in a significant negative shift in redox potential of 350 mV (from -0.814 to -1.164 V vs. SHE), enabling a record-high cell voltage of 1.63 V in neutral ZIFBs. The stabilized coordination environment facilitates highly reversible Zn plating/stripping while suppressing hydrogen evolution, dendrite formation and other side reactions. As a result, such high-voltage ZIFB demonstrates a remarkable energy efficiency of 88.77% at 40 mA cm-2 and excellent cycling stability over 320 cycles, advancing durable and high-performance neutral ZIFBs.

Sustainable recycling of lithium-ion batteries (LIBs) is increasingly important as their deployment continues to expand. Therefore, recycling the widely practically applied LIBs cathode material, LiFePO4 (LFP), shows great importance to the conservation of lithium source. However, current technologies for spent LFP (sLFP) recycling and regeneration typically consume electrical energy or chemical reagents, increasing process cost and limiting economic viability. Here, we report a charging-free electrochemical system, which enables regenerating sLFP while simultaneously harvesting low-grade heat. Owing to the inversed spontaneous reaction direction between LFP and [Fe(CN)6]3-/4- achieved by temperature difference, the constructed system realized extracting Li+ from sLFP in one cell while embedding Li+ into sLFP in another cell. The developed system achieves a thermoelectric conversion efficiency of 5.26%, while the regenerated LFP delivers a discharge capacity of 153 mAh g⁻¹ at 0.1 C, recovering 90% of the theoretical capacity of LiFePO4. This work presents an environmentally friendly, low cost and promising pathway for simultaneous regeneration of sLIBs and low-grade heat harvesting.