Active Water Molecules Research Articles

Active Water Optimization in Different Electrolyte Systems for Stable Zinc Anodes.

Zinc (Zn) metal, with abundant resources, intrinsic safety, and environmental benignity, presents an attractive prospect as a novel electrode material. However, many substantial challenges remain in realizing the widespread application of aqueous Zn-ion batteries (AZIBs) technologies. These encompass significant material corrosion challenges (This can lead to battery failure in an unloaded state.), hydrogen evolution reactions, pronounced dendrite growth at the anode interface, and a constrained electrochemical stability window. Consequently, these factors contribute to diminished battery lifespan and energy efficiency while restricting high-voltage performance. Although numerous reviews have addressed the potential of electrode and separator design to mitigate these issues to some extent, the inherent reactivity of water remains the fundamental source of these challenges, underscoring the necessity for precise regulation of active water molecules within the electrolyte. In this review, the failure mechanism of AZIBs (unloaded and in charge and discharge state) is analyzed, and the optimization strategy and working principle of water in the electrolyte are reviewed, aiming to provide insights for effectively controlling the corrosion process and hydrogen evolution reaction, further controlling dendrite formation, and expanding the range of electrochemical stability. Furthermore, it outlines the challenges to promote its practical application and future development pathways.

Highly Reversible Aqueous Zinc-Ion Batteries via Multifunctional Hydrogen-Bond-Rich Dulcitol at Lower Temperature.

Aqueous zinc-ion batteries (AZIBs) are consideredoneofthemost promising next-generation energy storage devices due tocost-effectiveness and high safety. However, the uncontrolled dendrite growthandthe intolerance against low temperatures hinder the application of AZIBs. Herein, hydrogen-bonding-rich dulcitol (DOL) is introduced into the ZnSO4, which reshaped the hydrogen-bond network in the electrolyte and optimized the solvation sheath structure, effectively reducing the amount of active water molecules and inhibiting hydrogen evolution and the parasitic reaction at the zinc anode. In addition, higher adsorption energy DOL preferentially adsorbs on the surface of the zinc anode, guiding the uniform deposition of Zn2+ and inhibiting the formation of dendrites. DOL also enhances the interaction between free and free water and improves the resistance to freeze of the electrolyte. Consequently, the Zn//Zn symmetric cells assembled with DOL are extremely stable cycled for 2000h at 2mA cm-2. The NH4V4O10 (NVO)//Zn full cell showed more excellent specific capacity of 183.07 mAh g-1 after 800 cycles. Even at the low temperature of -10 °C, the cell still maintains 155.95 mAh g-1 capacity after 600 cycles. This work provides a new strategy for the subsequent study of AZIBs with high stability at low temperatures.

Characterization Techniques for Probing the Electrolyte Solvation Structures of Aqueous Zinc Metal Batteries

AbstractWhile aqueous zinc metal batteries (AZMBs) have shown great promise for large‐scale energy storage, a series of interfacial side reactions derived from the decomposition of active water molecules in the Zn2+ solvation structures seriously hinder the practical application of AZMBs. Recently, regulating the solvation structures of Zn2+ in electrolytes has been proven to be effective in alleviating the interfacial side reactions. Advanced characterization techniques to probe the solvation structures of electrolytes provide powerful tools for comprehensively understanding the underlying relationship between the solvation structures of electrolytes and the performance of AZMBs. Although significant processes have been achieved in electrolyte engineering and mechanistic understanding of the solvation structures has been preliminarily established, systematic summary of the characterization techniques for solvation structures is still absent. Considering the importance of the solvation structures in electrolyte engineering, a comprehensive review of this topic is necessary. In this review article, the advantages and application scope of the ever‐used characterization techniques in studying the solvation structures are introduced and the remaining challenges and the potential opportunities in the future are discussed.

Cation Enrichment Promotes High-rate CO Electroreduction to C2+ Liquid Products.

Electrochemical reduction of CO into valuable multicarbon (C2+) liquids is crucial for reducing CO2 emissions and advancing clean energy, yet mastering efficiency and selectivity in this process remains a tough challenge. Herein, we employ a surface-modification strategy using electrochemically active polymeric 1,4,5,8-naphthalenete-tracarboxylic dianhydride (PNTCDA)-modified copper nanosheets (PM-Cu) to rearrange reactive species in the electric double layer, where the PNTCDA triggers a distinctive enolization that anchor potassium ions (K+) onto the cathode surface under reduction condition. Electrochemical analysis and computational simulations revealed that this approach fine-tunes K+ distribution in the double layer, making the dehydration of hydrated K+ more efficient and reducing active water molecules at the interface, thus inhibiting the hydrogen evolution reaction while concurrently promoting CO reduction via enhanced C-C coupling. For the first time, the PM-Cu catalyst demonstrates ampere-scale current densities with the exclusive selectivity of a C2+ liquid product yield exceeding 90 %. Thus, by tailoring the local microenvironment with electrochemically active organics, it is possible to modulate CO reduction, improve sustainable energy storage, and increase industrial carbon utilization.

Self-Reinforced Cathode Interface to Prolong the Cyclic Stability of Zn-MnO2 Batteries.

Rechargeable aqueous zinc-ion batteries (RAZIBs) are attracting increasing attention due to their advantages in safety, cost, and energy density. However, the choice of electrode binders when using aqueous electrolytes faces many constraints, as nontoxic and low-cost hydrophilic binders, such as sodium alginate (SA), can lead to electrode damage due to excessive swelling in aqueous solution. Here, by employing double-network hydrogel electrolytes formed by poly(vinyl alcohol) and alginate, the content and activity of water molecules at the electrode-electrolyte interface are reduced, and the mechanical stability of the electrode is reinforced, thereby affording reliable protection to the cathode bonded with SA. The quasi-solid-state interface formed between SA and the gel electrolyte provides stable electrode architecture and smooth ion transport, thus enabling Zn||MnO2 cells to exhibit excellent electrochemical cycling performance even when using hydrophilic binders.

Pseudo-Solid Aqueous Electrolyte with Widened Potential Window By Encapsulating Water-in-Salt in Silica Matrix

Pseudo-solidification of liquid electrolytes is an effective means to prevent electrolyte leakage, and various polymeric materials have been proposed. Recently, silica gel prepared by sol-gel methods has been proposed as an inorganic polymer than can confine liquid electrolytes and has shown to be a promising pseudo-solidification method providing rigidity and stability owing to the inorganic matrix while maintaining the ionic conductivity of liquid electrolytes. For example, silica gel containing an ionic liquid, known as an ionogel, enables solidification while maintaining the properties of the ionic liquid1,2. Furthermore, by utilizing the high processability of the sol state, it becomes possible to achieve uniform interfaces with substrates and form thin films. In this study, we focused on Water-in-Salt (WiS) electrolytes3 as the liquid electrolyte to encapsulate in the silica matrix. WiS electrolytes are highly concentrated aqueous electrolytes with high safety and a wide electrochemical window.As the WiS, 21 m (m: mol kg–1) LiTFSI (lithium bis(trifluoromethane sulfonyl)imide) was chosen and confined within a silica matrix by sol-gel methods. The 21 m LiTFSI silica gel was prepared by mixing tetraethoxysilane into a 21 m LiTFSI solution by modification of the synthesis of an ionogel.2 During this process, the water content within the matrix is sensitive to the humidity of the environment, thus control of humidity during the synthesis is crucial.21 m LiTFSI silica gel obtained under suitable humidity exhibited high transparency. The LiTFSI concentration measured by thermogravimetry was 20.5 m, close to the intended concentration of 21 m. The activation energy evaluated from electrochemical impedance spectroscopy using a two-electrode Swagelok cell (Pt | 21 m LiTFSI silica gel | Pt) showed a value similar to that of the 21 m LiTFSI solution, showing that the silica matrix does not affect the conduction mechanism of the confined 21 m LiTFSI solution.Interestingly, in the 21 m LiTFSI silica gel, a change in the activity of water molecules was observed compared to the liquid system with the same concentration. From the Raman spectrum, the 21 m LiTFSI silica gel exhibited an S–N–S bending vibration peak at a higher wavenumber compared to the liquid system. It is known that with the increase in salt concentration and the decrease in free water content in LiTFSI aqueous solutions, the interaction between Li+ and TFSI– strengthens, resulting in a shift of the S–N–S bending vibration peak of TFSI– to a higher wavenumber.REF This result suggests that the activity of water molecules in the 21 m LiTFSI within the silica matrix is reduced compared to the liquid system. The potential window of the 21 m LiTFSI silica gel was evaluated by cyclic voltammetry. A glassy carbon electrode coated with 21 m LiTFSI silica gel as the working electrode was immersed in a 21 m LiTFSI solution (v = 2 mV s–1, E = –2.2 to 2.2 V vs. RHE). The potential window of the 21 m LiTFSI solution was 2.97 V, while for 21 m LiTFSI silica gel the potential window was widened to 3.33 V. In highly concentrated aqueous electrolytes, the activity of water molecules affects the decomposition potential, and it is known that the potential window expands as the concentration of salt increases, due to the decrease in the activity of water.3,4 Therefore, the expansion of the potential window in the case of 21 m LiTFSI silica gel can be attributed to the decrease in the activity of water. References (1) D. S. Ashby, R. H. DeBlock, C.-H. Lai, C. S. Choi and B. S. Dunn, Joule, 1, 344 (2017).(2) G. Tan, F. Wu, C. Zhan, J. Wang, D. Mu, J. Lu and K. Amine, Nano Lett., 16, 1960 (2016).(3) L. Suo, O. Borodin, T. Gao, M. Olguin, J. Ho, X. Fan, C. Luo, C. Wang and K. Xu, Science, 350, 938 (2015).(4) Y. Yamada, K. Usui, K. Sodeyama, S. Ko, Y. Tateyama and A. Yamada, Nat. Energy, 1, 16129 (2016). Figure 1

Organic-inorganic hybrid cathode enabled by in-situ interface polymerization engineering boosts Zn2+ desolvation in aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have attracted considerable attention for application in large-scale energy storage systems. However, the progress of RAZIBs has been hindered by the sluggish reaction kinetics and poor structural stability, which are closely associated with the desolvation process of hydrated Zn2+. To overcome these issues, an in situ interfacial polymerization strategy is proposed to uniformly germinate a polyaniline (PANI) layer on α-MnO2 and form an organic–inorganic hybrid cathode (MnO2@PANI). Theoretical calculations and experimental characterizations disclose that the polyaniline layer equipped with hydrophilic functional groups can effectively trap the active water molecules to break the strong attraction between H2O and Zn2+, thereby facilitating the desolvation process of hydrated Zn2+, and regulating the Zn2+ diffusion kinetics and electrode reaction kinetics on the cathode/electrolyte surface. Meanwhile, the irreversible phase evolution and dissolution of active species are largely suppressed due to the PANI shell protecting the α-MnO2 from the attack of active water molecules. As a consequence, the organic–inorganic hybrid cathode exhibits 401.9 mAh/g after 200 cycles at a current density of 0.5 A/g and long-term durability over 1000 cycles at a current density of 2.0 A/g without irreversible phase transformation. This work provides insight into the regulation of the desolvation process for high performance aqueous energy storage systems.

Confined Water Dynamics in Topological Networks Hydrogel for Aqueous Electrochemical Devices.

The unique properties of confined water molecules within polymer networks have garnered extensive research interest in energy storage, catalysis, and sensing. Confined water molecules exhibit higher thermodynamic stability compared to free water, which reduces decomposition and evaporation of water in hydrogel electrolyte system. Herein, a facile strategy is developed to limit active water molecules in a hydrogel network via hydrogen bonding within a topological network. The design of this gel enhances hydrogen bonding between the gel network and water molecules, thereby improving stability by constructing interpenetrating networks. Using this design, the topological network gel is selected as the electrolyte for batteries, demonstrating an extended electrochemical window from 2.37V with polyvinyl alcohol gel to 2.96V, indicating superior confinement of water molecules by hydrogen bonds in the topological network. Additionally, batteries and capacitors assembled with the topological gel exhibit high-capacity retention rates of 94.25% after 20000 cycles at a current density of 1.0 A g-1 and 87.63% after 10000 cycles at a current density of 0.5 A g-1, respectively. This study demonstrates the feasibility of using a topological gel design to enhance gel electrolyte stability, offering a promising avenue for future research in regulating topological networks within gels for various applications.

Fluoro-polymer/TiO2 based photocatalysts for high efficiency hydrogen generation

In view of limited number of studies on photoreforming of synthetic polymers, herein, a series of new glycopolymers are synthesized via RAFT polymerization to obtain diblock copolymers containing fluorinated and non-fluorinated segments in the glucopyranoside. These glycopolymers are used as probes to investigate photocatalytic reactions at different pH values of the modulated TiO2 photocatalyst. Through structural and surface characterizations, photocatalytic activities are investigated. Fluoro-polymers with deacetylated glucose, hydrophilic segment, PGD such as PPFPM-b-PGD and PPFBM-b-PGD could synergistically increase hydrogen generation rate up to 1368 μmol g-1h−1 and 1549 μmol g-1h−1 with quantum yields of 3.34 % and 3.79 % compared to non-fluoro glycopolymers. The presence of both fluorinated and non-fluorinated groups in diblock copolymers enhanced the rate of photocatalytic hydrogen generation compared to the homopolymer. The accelerated photo-reforming is attributed to in-situ fluorine-doped TiO2 along with high affinity and activation of water molecules. These polymers can generate hydrogen via photo-reforming process.

Symmetry Donor-Acceptor Molecule Regulating Hydrogen-Bonding Network for Improved Metal Zinc Anode.

The issues of zinc dendrites and side reactions caused by active water molecules have seriously affected the development of aqueous zinc batteries (AZBs). Herein, a symmetry hydrogen-bond donor-acceptor molecule additive named 1,3-bis(hydroxymethyl)urea (BHMU) can preferentially adsorb on the anode surface and lock up water molecules through hydrogen bonding, thus isolating water molecules and reducing side reactions caused by active water molecules. With these advantages, the mixed electrolyte containing BHMU additive impels a reversible Zn anode with a high Coulombic efficiency (99.7% over 1000 cycles at 1 mA cm-2), while it also enables a stable symmetric cell operated at 1 mA cm-2 (1 mAh cm-2, 6.89% DODZn) for 2250 h and 10 mA cm-2 (10 mAh cm-2, 68.9% DODZn) for 350 h. More importantly, the Zn||PTO full battery also delivered superior cycling stability and higher capacity after 3000 consecutive 3000 cycles of circulation at 5 A g-1. This study has great significance for the use of symmetry donor-acceptor molecules to modulate the solvation structure and the interface stability of the Zn anode in aqueous electrolytes.

Solvation Modification and Interfacial Chemistry Regulation Via Amphoteric Amino Acids for Long‐Cycle Zinc Batteries

AbstractTo address the issues of dendrite growth and zinc corrosion in rechargeable zinc‐air batteries, multifunctional glycine/valine additives are introduced into the electrolyte. By regulating the solvation shell structure and enhancing interfacial stability, these additives aim to protect the reversibility and stability of the zinc anode. Glycine/valine molecules inhibit the formation of the [Zn(H2O)6]2+ and Zn5(OH)8(OAc)2·2H2O by‐products at the interface by replacing active water molecules in a strong alkaline environment. Additionally, they form a hydrophobic electric double layer on the zinc metal surface, during the charge/discharge process, and construct an in situ solid electrolyte interface layer. This further suppresses the hydrogen evolution reaction and dendrite growth. The superior long‐term cycling stability of Zn||Zn cells, Zn||Cu, and zinc‐air full cells demonstrates the effectiveness of glycine/valine additives.

Suppressing hydrogen evolution reaction by constructing interfacial proton blocking layer for highly reversible zinc anode

Zinc (Zn) anodes are severely threatened by the hydrogen evolution reaction (HER) triggered by highly active water molecules. Motivated by the process of the HER in weakly acidic aqueous, we propose a strategy to construct a proton-blocking layer at the electrode-electrolyte interface by introducing robust hydrogen bonding, aiming to significantly suppress the HER. Isonicotinic acid (INA) possesses N and carboxyl sites that can form strong interactions with protons and can adsorb onto the surface of Zn. Thus, by introducing trace amounts (10 mM) of INA into the electrolyte, proton transfer at the interface can be effectively impeded. In addition, INA can also facilitate Zn uniform growth and inhibit dendrite formation. Consequently, the Zn//Zn symmetrical battery can perform for 3400 h at 1 mA/cm2@1 mAh/cm2, and the coulombic efficiency of the Zn//Cu battery can reach 99.74 % after 1800 cycles. Furthermore, due to the suppression of HER, the Zn//MnO2 batteries achieved high performance of 79.3 mAh/g after 2000 cycles at the current density of 2 A/g. This study provides a new approach to suppress HER and improve the stability of Zn anode.

Plasmonic Pt-PPCN/TiN Ohmic Junction for Photo-Thermo Catalytic Hydrogen Production.

The rational design of photocatalysts for improving the conversion of solar energy into hydrogen is a promising route for achieving carbon neutrality. Herein, we couple plasmonic titanium nitride (TiN) with highly crystalline potassium-doped polymeric carbon nitride (PPCN) to construct a PPCN/TiN ohmic junction. Such an ohmic junction not only broadens the absorption spectrum but also inhibits the recombination of electrons and holes. In addition, Pt nanoparticles are introduced into this ohmic junction to form plasmonic Pt-PPCN/TiN, improving the capture of hot electrons generated by TiN and thereby promoting the dissociation of the O-H bond in H2O. The energy barrier decreases from 0.7 to 0.2 eV. Enhanced separation of carrier, activation of water molecules, and capture of hot electrons are jointly promoting photo-thermo catalytic hydrogen production. Therefore, under full-spectrum irradiation, the hydrogen production rate of Pt-PPCN/TiN reaches 19 085 μmol g-1 h-1. This novel plasmonic photocatalyst is promising for full-spectrum photo-thermo catalytic hydrogen production.

Stabilizing Zinc Anode through Ion Selection Sieving for Aqueous Zn-Ion Batteries.

Uncontrollable dendrite growth and corrosion induced by reactive water molecules and sulfate ions (SO42-) seriously hindered the practical application of aqueous zinc ion batteries (AZIBs). Here we construct artificial solid electrolyte interfaces (SEIs) realized by sodium and calcium bentonite with a layered structure anchored to anodes (NB@Zn and CB@Zn). This artificial SEI layer functioning as a protective coating to isolate activated water molecules, provides high-speed transport channels for Zn2+, and serves as an ionic sieve to repel negatively charged anions while attracting positively charged cations. The theoretical results show that the bentonite electrodes exhibit a higher binding energy for Zn2+. This demonstrates that the bentonite protective layer enhances the Zn-ion deposition kinetics. Consequently, the NB@Zn//MnO2 and CB@Zn//MnO2 full-battery capacities are 96.7 and 70.4 mAh g-1 at 2.0 A g-1 after 1000 cycles, respectively. This study aims to stabilize Zn anodes and improve the electrochemical performance of AZIBs by ion-selection sieving.

Improving the Photoactivity of Porphyrin-Based Metal-Organic Frameworks via Constructing [Ce-O] Active Site and Vacancy.

Defect engineering of metal-organic frameworks (MOFs) is a versatile approach to tailoring their electronic structures and photocatalytic performance. Herein, Ce-based porphyrin MOFs (CMFs) featuring controlled structural defects were successfully prepared using a simple acid modulation strategy to drive the photocatalytic H2 generation. The [Ce-O] unit serves as the active site via a ligand-to-metal charge transfer process, which has been confirmed by in situ XPS analysis. Abundant exposed coordinatively unsaturated Ce-O centers are beneficial for the adsorption and activation of water molecules, which is an important factor for improving the photocatalytic performance of the synthesized defective MOFs. In addition, optical and electrochemical experiments indicate that CMFs with more oxygen vacancies possess higher charge separation efficiency. As a result, the optimized CMF(Zn)-200 sample afforded high stability and activity in the H2 generation (up to 1603.3 μmol·g-1·h-1 under cocatalyst-free conditions) and tetracycline hydrochloride removal efficiency (97%), which was 8.45 and 97 times higher than that of pure meso-tetra(4-carboxyphenyl)porphine. This study demonstrates that effective structural modulation and defect introduction can improve the activity and stability of PMOF-based photocatalysts.

In Situ Assembly of Metal‐Organic Coordination Polymer Layers Enables Highly Reversible Zn Anodes with a Long Cycle Life of over 6900 h

AbstractZn anodes in aqueous zinc‐ion batteries chronically suffer from pernicious side reactions and ineluctable dendrite growth, resulting in inadequate reversibility and suboptimal Coulombic efficiency (CE) and impeding commercialization. Herein, a multifunctional metal–organic coordination polymer layer (FAZ) is constructed on the zinc anode surface (FAZ@Zn) utilizing a simple self‐assembly strategy. The zincophilic FAZ interfacial layer with a high Zn2+ transfer number and low nucleation barrier effectively facilitates the de‐solvation process, supports the rapid transport of zinc ions, and contributes to the preferential growth of Zn (002) crystal planes, enabling dendrite‐free Zn deposition. Furthermore, the FAZ layer, as an interfacial pH regulating layer, effectively inhibits the direct contact between Zn and active water molecules, lowering the severity of side reactions. Consequently, the FAZ@Zn anode furnishes an eminent cycle stability over 6900 h, with a low polarization voltage at 1 mA cm−2 and 1 mA h cm−2 and a boosted CE of 99.88% over 4100 cycles. More encouragingly, when coupled with Na2V6O16·3H2O, the FAZ@Zn anode enables the full cell to deliver satisfactory rate performance and a 97% capacity retention over 1600 cycles. This work provides a simple strategy for the effective preparation of highly reversible zinc anodes for high‐performance aqueous zinc‐ion batteries.

Simultaneous regulation on solvation shell and electrode interface for sustainable zinc-based flow batteries

The practical implementation of Zn-based flow batteries encounters the challenges associated with uneven deposition of Zn ions and undesirable side reactions. Here, a hybrid Zn-based electrolyte system composed of ZnBr2, ethylene glycol (EG), H2O and potassium gluconate (KGlu) is developed as anolyte to modulate the solvation structure and interface engineering for a sustainable Zn-based flow battery. The EG molecules could exclude water molecules outside the solvation structure, inhibiting the water-induced side reactions and Zn corrosion. Moreover, the incorporation of potassium gluconate constructs an artificial stable anionic interface for dendrite-free Zn deposition. Chemical stability and hydrogen evolution potential tests demonstrate that the activity of water molecules could be suppressed in the EG-containing hybrid electrolyte. Deposition morphologies and Zn//Zn symmetric flow battery tests also reveal that gluconate anions preferentially adsorbed on zinc anode could effectively facilitate uniform zinc deposition. As a result, the Zn-based flow battery with the proposed hybrid electrolyte delivers a stable cycling performance over 200 cycles and high reversibility with an average CE of over 97.4 % at 20 mA cm−2, exhibiting a peak power density of 103.2 mW cm−2. This work provides a universal electrolyte design strategy for realizing a sustainable Zn-based flow battery.

Electric‐Responded 2D Black Phosphorus Nanosheets Induce Uniform Zn2+ Deposition for Efficient Aqueous Zinc‐Metal Batteries

AbstractAqueous zinc‐metal batteries (AZMBs) have demonstrated inspiring potential for large‐scale energy storage applications. However, their further utilization is impeded by issues such as severe side reactions and the uncontrolled penetrating dendrites growth. In this study, an innovative approach to modify the aqueous electrolyte with 2D black phosphorus nanosheets (denoted as 2D BP nanosheets) is proposed. The 2D BP nanosheets under the electric field acted as a unique electron directional migration character, can dynamically homogenize the electric field, facilitate homogeneous Zn2+ conduction. The nanosheets covering on the protuberances can also induce stable and homogeneous Zn2+ deposition, thereby effectively inhibit the formation of penetrating dendrites. More importantly, this special protective interlayer can further prevent the direct contact between reactive Zn‐metal and activated water molecules, thereby inhibiting the occurrence of undesirable side‐reactions. The incorporation of BP nanosheets induced significant improvement in electrochemical stability and reversibility for AZMBs. As a result, Zn//Zn symmetric batteries based on 2D BP nanosheets added electrolyte exhibited steady cycling for over 2800 h at 1 mA cm−2 1 mAh cm−2. Zn//NVO full‐cell preserved 78.85% capacity even after ultra‐long 1000 cycles. The successful application of 2D BP nanosheets introduce a novel method to accelerate the practical application of AZMBS.

In-situ physical/chemical cross-linked hydrogel electrolyte achieving ultra-stable zinc anode-electrolyte interface towards dendrite-free zinc ion battery

Hydrogen evolution reaction (HER), zinc corrosion, and dendrites growth on zinc metal anode are the major issues limiting the practical applications of zinc-ion batteries. Herein, an in-situ physical/chemical cross-linked hydrogel electrolyte (carrageenan/polyacrylamide/ZnSO4, denoted as CPZ) has been developed to stabilize the zinc anode-electrolyte interface, which can eliminate side reactions and prevent dendrites growth. The in-situ CPZ hydrogel electrolyte improves the reversibility of zinc anode due to eliminating side reactions caused by active water molecules. Furthermore, the electrostatic interaction between the SO4−· groups in CPZ and Zn2+ can encourage the preferential deposition of zinc atoms on (002) crystal plane, which achieve dendrite-free and homogeneous zinc deposition. The in-situ hydrogel electrolyte offers a streamlined approach to battery manufacturing by allowing for direct integration into the battery. Subsequently, the Zn//Zn half battery with CPZ hydrogel electrolyte can enable an ultra-long cycle over 5500 h at a current density of 0.5 mA cm−2, and the Zn//Cu half battery reach an average coulombic efficiency of 99.37%. The Zn//V2O5-GO full battery with CPZ hydrogel electrolyte demonstrates 94.5% of capacity retention after 2100 cycles. This study is expected to open new thought for the development of commercial hydrogel electrolytes for low-cost and long-life zinc-ion batteries.

Engineering hydrophobic protective layers on zinc anodes for enhanced performance in aqueous zinc-ion batteries

Aqueous zinc-ion batteries possess substantial potential for energy storage applications; however, they are hampered by challenges such as dendrite formation and uncontrolled side reactions occurring at the zinc anode. In our investigation, we sought to mitigate these issues through the utilization of in situ zinc complex formation reactions to engineer hydrophobic protective layers on the zinc anode surface. These robust interfacial layers serve as effective barriers, isolating the zinc anode from the electrolyte and active water molecules and thereby preventing hydrogen evolution and the generation of undesirable byproducts. Additionally, the presence of numerous zincophilic sites within these protective layers facilitates uniform zinc deposition while concurrently inhibiting dendrite growth. Through comprehensive evaluation of functional anodes featuring diverse functional groups and alkyl chain lengths, we meticulously scrutinized the underlying mechanisms influencing performance variations. This analysis involved precise modulation of interfacial hydrophobicity, rapid Zn2+ ion transport, and ordered deposition of Zn2+ ions. Notably, the optimized anode, fabricated with octadecylphosphate (OPA), demonstrated exceptional performance characteristics. The Zn//Zn symmetric cell exhibited remarkable longevity, exceeding 4000 h under a current density of 2 mA cm−2 and a capacity density of 2 mA h cm−2. Furthermore, when integrated with a VOH cathode, the complete cell exhibited superior capacity retention compared to anodes modified with alternative organic molecules.