Engineering Covalent Organic Frameworks Toward Advanced Zinc-Based Batteries.

Zinc-based batteries (ZBBs) have demonstrated considerable potential among secondary batteries, attributing to their advantages including good safety, environmental friendliness, and high energy density. However, ZBBs still suffer from issues such as the formation of zinc dendrites, occurrence of side reactions, retardation of reaction kinetics, and shuttle effects, posing a great challenge for practical applications. As promising porous materials, covalent organic frameworks (COFs) and their derivatives have rigid skeletons, ordered structures, and permanent porosity, which endow them with great potential for application in ZBBs. This review, therefore, provides a systematic overview detailing on COFs structure pertaining to electrochemical performance of ZBBs, following an in depth discussion of the challenges faced by ZBBs, which includes dendrites and side reactions at the anode, as well as dissolution, structural change, slow kinetics, and shuttle effect at the cathode. Then, the structural advantages of COF-correlated materials and their roles in various ZBBs are highlighted. Finally, the challenges of COF-correlated materials in ZBBs are outlined and an outlook on the future development of COF-correlated materials for ZBBs is provided. The review would serve as a valuable reference for further research into the utilization of COF-correlated materials in ZBBs.

Covalent Organic Framework with 3D Ordered Channel and Multi-Functional Groups Endows Zn Anode with Superior Stability.

Achieving a highly robust zinc (Zn) metal anode is extremely important for improving the performance of aqueous Zn-ion batteries (AZIBs) for advancing "carbon neutrality" society, which is hampered by the uncontrollable growth of Zn dendrite and severe side reactions including hydrogen evolution reaction, corrosion, and passivation, etc. Herein, an interlayer containing fluorinated zincophilic covalent organic framework with sulfonic acid groups (COF-S-F) is developed on Zn metal (Zn@COF-S-F) as the artificial solid electrolyte interface (SEI). Sulfonic acid group (- SO3H) in COF-S-F can effectively ameliorate the desolvation process of hydrated Zn ions, and the three-dimensional channel with fluoride group (-F) can provide interconnected channels for the favorable transport of Zn ions with ion-confinement effects, endowing Zn@COF-S-F with dendrite-free morphology and suppressed side reactions. Consequently, Zn@COF-S-F symmetric cell can stably cycle for 1,000 h with low average hysteresis voltage (50.5 mV) at the current density of 1.5 mA cm-2. Zn@COF-S-F|MnO2 cell delivers the discharge specific capacity of 206.8 mAh g-1 at the current density of 1.2 A g-1 after 800 cycles with high-capacity retention (87.9%). Enlightening, building artificial SEI on metallic Zn surface with targeted design has been proved as the effective strategy to foster the practical application of high-performance AZIBs.

Separator designs for aqueous zinc-ion batteries.

Aqueous zinc-ion batteries (AZIBs) are attracting worldwide attention due to their multiple merits such as extreme safety, low cost, feasible assembly, and environmentally friendly enabled by water-based electrolytes. At present, AZIBs have experienced systematic advances in battery components including cathode, anode, and electrolyte, whereas research involving separators is insufficient. The separator is the crucial component of AZIBs through providing ion transport, forming contact with electrodes, serving as a container for electrolyte, and ensuring the efficient battery operation. Considering this great yet ignored significance, it is timely to present the latest advances in design strategies, the systematic classification and summary of separators. We summarize the separator optimization strategies mainly along two approaches including the modification of the frequently used glass fiber and the exploitation of new separators. The advantages and disadvantages of the two strategies are analyzed from the material types and the characteristics of different strategies. The effects and mechanisms of various materials on regulating the uniform migration and deposition of Zn2+, balancing the excessively concentrated nucleation points, inhibiting the growth of dendrites, and the occurrence of side reactions were discussed using confinement, electric field regulation, ion interaction force, desolvation, etc. Finally, potential directions for further improvement and development of AZIBs separators are proposed, aiming at providing helpful guidance for this booming field.

Zinc-Bismuth Binary Alloy Enabling High-Performance Aqueous Zinc Ion Batteries.

Reconfiguration of zinc anodes efficiently mitigates dendrite formation and undesirable side reactions, thus favoring the long-term cycling performance of aqueous zinc ion batteries (AZIBs). This study synthesizes a Zn@Bi alloy anode (Zn@Bi) using the fusion method, and find that the anode surfaces synthesized using this method have an extremely high percentage of Zn(002) crystalline surfaces. Experimental results indicate that the addition of bismuth inhibits the hydrogen evolution reaction and corrosion of zinc anodes. The finite-element simulation results indicate that Zn@Bi can effectively achieve a uniform anodic electric field, thereby regulating the homogeneous depositions of zinc ions and reducing the production of Zn dendrite. Theoretical calculations reveal that the incorporation of Bi favors the anode structure stabilization and higher adsorption energy of Zn@Bi corresponds to better Zn deposition kinetics. The Zn@Bi//Zn@Bi symmetric cell demonstrates an extended cycle life of 1000 h. Furthermore, when pairing Zn@Bi with an α-MnO2 cathode to construct a Zn@Bi//MnO2 cell, a specific capacity of 119.3 mAh g-1 is maintained even after 1700 cycles at 1.2 A g-1 . This study sheds light on the development of dendrite-free anodes for advanced AZIBs.

Biomass-derived carbon materials for vanadium redox flow battery: From structure to property.

Biomass-derived carbon (BDC) materials are suitable as electrode or catalyst materials for vanadium redox flow battery (VRFB), owing to the characteristics of vast material sources, environmental friendliness, and multifarious structures. A timely and comprehensive review of the structure and property significantly facilitates the development of BDC materials. Here, the paper starts with the preparation of biomass materials, including carbonization and activation. It is designed to summarize the lastest developments in BDC materials of VRFB in four different structural dimensions from zero dimension (0D) to three dimension (3D). Every dimension begins with meticulously selected examples to introduce the structural characteristics of materials and then illustrates the improved performance of the VRFB due to the structure. Simultaneously, challenges, solutions, and prospects are indicated for the further development of BDC materials. Overall, this review will help researchers select excellent strategies for the fabrication of BDC materials, thereby facilitating the use of BDC materials in VRFB design.

Stabilizing Zn Metal Anode Through Regulation of Zn Ion Transfer and Interfacial Behavior with a Fast Ion Conductor Protective Layer.

Aqueous Zn-ion batteries (AZIBs) attract intensive attention owing to their environmental friendliness, cost-effectiveness, innate safety, and high specific capacity. However, the practical applications of AZIBs are hindered by several adverse phenomena, including corrosion, Zn dendrites, and hydrogen evolution. Herein, a Zn anode decorated with a 3D porous-structured Na3 V2 (PO4)3 (NVP@Zn) is obtained, where the NVP reconstruct the electrolyte/anode interface. The resulting NVP@Zn anode can provide a large quantity of fast and stable channels, facilitating enhanced Zn ion deposition kinetics and regulating the Zn ions transport process through the ion confinement effect. The NASICON-type NVP protective layer promote the desolvation process due to its nanopore structure, thus effectively avoiding side reactions. Theoretical calculations indicate that the NVP@Zn electrode has a higher Zn ion binding energy and a higher migration barrier, which demonstrates that NVP protective layer can enhance Zn ion deposition kinetics and prevent the unfettered 2D diffusion of Zn ions. Therefore, the results show that NVP@Zn/MnO2 full cell can maintain a high specific discharge capacity of 168 mAh g-1 and a high-capacity retention rate of 74.6% after cycling. The extraordinary results obtained with this strategy have confirmed the promising applications of NVP in high-performance AZIBs.

Biochar/layered double hydroxides composites as catalysts for treatment of organic wastewater by advanced oxidation processes: A review.

Heterogeneous advanced oxidation process has been widely studied as an effective method for removing organic pollutants in wastewater, but the development of efficient catalysts is still challenging. This review summaries the present status of researches on biochar/layered double hydroxides composites (BLDHCs) as catalysts for treatment of organic wastewater. The synthesis methods of layered double hydroxides, the characterizations of BLDHCs, the impacts of process factors influencing catalytic performance, and research advances in various advanced oxidation processes are discussed in this work. The integration of layered double hydroxides and biochar provides synthetic effects for improving pollutant removal. The enhanced pollutant degradation in heterogeneous Fenton, sulfate radical-based, sono-assisted, and photo-assisted processes using BLDHCs have been verified. Pollutant degradation in heterogeneous advanced oxidation processes using BLDHCs is influenced by process factors such as catalyst dosage, oxidant addition, solution pH, reaction time, temperature, and co-existing substances. BLDHCs are promising catalysts due to the unique features including easy preparation, distinct structure, adjustable metal ions, and high stability. Currently, catalytic degradation of organic pollutants using BLDHCs is still in its infancy. More researches should be conducted on the controllable synthesis of BLDHCs, the in-depth understanding of catalytic mechanism, the improvement of catalytic performance, and large-scale application of treating real wastewater.

Polyaniline functionalized separator as synergistic medium for aqueous zinc-ion batteries.

Aqueous zinc-ion batteries (AZIBs) have received increasing attention as a promising energy storage device. However, it was rarely reported that the separators as a synergistic medium stabilize the cathode and anode materials. Herein, a polyaniline functionalized glass fiber separator (PANI-GF) was synthesized in situ. The porous structure of PANI effectively regulated the flux of zinc ions inside the separator and its deposition behavior through ion confinement. The abundant N-containing functional groups can adsorb water molecules and effectively reduce harmful side reactions. Moreover, the PANI-GF separator adjusted pH to inhibit dissolution of the cathode by protonation. Importantly, based on the synergistic separator, the Zn-MnO2 full cell exhibited more than twice discharge capacity compared to the conventional cell after 1000 cycles at 2 A g-1. This study provided in-depth insight into the design of convenient, reliable, cost-effective, and synergistic separators for AZIBs.

A smelting-rolling strategy for ZnIn bulk phase alloy anodes.

Reversibility and stability are considered as the key indicators for Zn metal anodes in aqueous Zn-ion batteries, yet they are severely hindered by uncontrolled Zn stripping/plating and side reactions. Herein, we fabricate a bulk phase ZnIn alloy anode containing trace indium by a typical smelting-rolling process. A uniformly dispersed bulk phase of the whole Zn anode is constructed rather than only a protective layer on the surface. The Zn deposition can be regarded as instantaneous nucleation due to the adsorption of the evenly dispersed indium, and formation of the exclusion zone for further nucleation can be prevented at the same time. Owing to the bulk phase structure of ZnIn alloy, the indium not only plays a crucial role in Zn deposition, but also improves the Zn stripping. Consequently, the as-designed ZnIn alloy anode can sustain stable Zn stripping/plating for over 2500 h at 4.4 mA cm-2 with nearly 6 times smaller voltage hysteresis than that of pure Zn. Moreover, it enables a substantially stable ZnIn//NH4V4O10 battery with 96.44% capacity retention after 1000 cycles at 5 A g-1. This method of regulating the Zn nucleation by preparing a Zn-based alloy provides a potential solution to the critical problem of Zn dendrite growth and by-product generation fundamentally.

Metal-Organic Frameworks Functionalized Separators for Robust Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) are one of the promising energy storage systems, which consist of electrode materials, electrolyte, and separator. The first two have been significantly received ample development, while the prominent role of the separators in manipulating the stability of the electrode has not attracted sufficient attention. In this work, a separator (UiO-66-GF) modified by Zr-based metal organic framework for robust AZIBs is proposed. UiO-66-GF effectively enhances the transport ability of charge carriers and demonstrates preferential orientation of (002) crystal plane, which is favorable for corrosion resistance and dendrite-free zinc deposition. Consequently, Zn|UiO-66-GF-2.2|Zn cells exhibit highly reversible plating/stripping behavior with long cycle life over 1650 h at 2.0 mA cm-2, and Zn|UiO-66-GF-2.2|MnO2 cells show excellent long-term stability with capacity retention of 85% after 1000 cycles. The reasonable design and application of multifunctional metal organic frameworks modified separators provide useful guidance for constructing durable AZIBs.

A Review on 3D Zinc Anodes for Zinc Ion Batteries.

Zinc ion batteries (ZIBs) have been gradually developed in recent years due to their abundant resources, low cost, and environmental friendliness. Therefore, ZIBs have received a great deal of attention from researchers, which are considered as the next generation of portable energy storage systems. However, poor overall performance of ZIBs restricts their development, which is attributed to zinc dendrites and a series of side reactions. Constructing 3D zinc anodes has proven to be an effective way to significantly improve their electrochemical performance. In this review, the challenges of zinc anodes in ZIBs, including zinc dendrites, hydrogen evolution and corrosion, as well as passivation, are comprehensively summarized and the energy storage mechanisms of the zinc anodes and 3D zinc anodes are discussed. 3D zinc anodes with different structures including fiberous, porous, ridge-like structures, plated zinc anodes on different substrates and other 3D zinc anodes, are subsequently discussed in detail. Finally, emerging opportunities and perspectives on the material design of 3D zinc anodes are highlighted and challenges that need to be solved in future practical applications are discussed, hopefully illuminating the way forward for the development of ZIBs.

Facile synthesis of magnetic ZnFe2O4/AC composite to activate peroxydisulfate for dye degradation under visible light irradiation.

Heterogeneous photocatalysis/persulfate oxidation process has been considered as a promising technology for dye contaminants removal. The magnetic ZnFe2O4/active carbon (AC) composites were hydrothermally synthesized and firstly used to activate peroxydisulfate (PDS) for rhodamine B (RhB) degradation under visible LED light irradiation. The optimized Vis-ZnFe2O4/AC(4/1)-PDS system can enhance the RhB degradation efficiency by 32.01% and 13.87% compared with Vis-ZnFe2O4-PDS and Vis-AC-PDS systems, respectively. The influence of operational parameters such as catalyst dosage (0.2 - 0.4 g L-1), PDS concentration (1.0 - 2.0 g L-1), temperature (25 - 45 °C), solution pH (2.7 - 10.9), and coexisting inorganic ions (Cl-, NO3-, HCO3-, PO43-, Cu2+, Fe3+, and Ca2+) on RhB degradation was studied, and 100% of RhB (20 mg L-1) was degraded after 80 min at operational condition: 0.30 g L-1 of ZnFe2O4/AC(4/1) and 1.5 g L-1 of PDS, solution pH of 2.74, reaction temperature of 25 °C. The quenching experiments, EPR test, and XPS analysis were employed to reveal the proposed mechanism, which demonstrated that 1O2 played a more important role than other reactive species (SO4•-, •OH, O2•-, and h+) in RhB degradation. The generation of 1O2 via the two routes was as follows: (i) the in situ formed active oxygen (O*) reacted with HSO5- to produce 1O2; (ii) O2•- was oxidized by h+ to form 1O2. After five consecutive cycles, the photodegradation efficiency of RhB by ZnFe2O4/AC(4/1) catalyst slightly decreased from 88.52 to 83.92%, indicating the excellent reusability of ZnFe2O4/AC(4/1) photocatalyst. As designed, Vis-ZnFe2O4/AC-PDS oxidation system can effectively remove RhB from the different real water matrices, and the degradation efficiency of RhB in tap water, river water, and secondary effluent was 78.24%, 79.55%, and 74.53% after 80 min of reaction, respectively.

Dual metal ions and water molecular pre-intercalated δ-MnO2 spherical microflowers for aqueous zinc ion batteries.

Layered δ-MnO2 is a promising cathode material for aqueous zinc ion batteries (AZIBs) due to its high theoretical capacity, high operating voltage and low cost. However, the dissolution of MnO2 and the disproportionation of Mn3+ will lead to irreversible reaction and serious structural degradation of the material during cycling process. In this work, the Al3+ pre-intercalated K0.27MnO2·0.54H2O was prepared by a one-step hydrothermal method with citric acid as the complexing agent and weak reducing agent. Based on the pillars of bimetallic ions K+, Al3+ and water, the framework and interlayer of δ-MnO2 is stabilized. Besides, a certain amount of Al3+ facilitates the increase of crystal water compared with the pure K0.27MnO2·0.54H2O, which is not only conducive to promote the construction of porous and loose 3D morphology, but also beneficial to improve the stability of layered structure and accelerate the migration rate of zinc ions. Contributed to the dissolution/deposition reaction mechanism combined with H+/Zn2+ co-insertion/co-extraction mechanism, it has achieved the high capacity with the maximum reversible specific capacity of 269.5 mAh g-1 at 0.5 A g-1 and excellent stability with 205.8 mAh g-1 even after 300 cycles in Zn//Al-KMO battery.

Interfacial Engineering Strategy for High-Performance Zn Metal Anodes.

Due to their high safety and low cost, rechargeable aqueous Zn-ion batteries (RAZIBs) have been receiving increased attention and are expected to be the next generation of energy storage systems. However, metal Zn anodes exhibit a limited-service life and inferior reversibility owing to the issues of Zn dendrites and side reactions, which severely hinder the further development of RAZIBs. Researchers have attempted to design high-performance Zn anodes by interfacial engineering, including surface modification and the addition of electrolyte additives, to stabilize Zn anodes. The purpose is to achieve uniform Zn nucleation and flat Zn deposition by regulating the deposition behavior of Zn ions, which effectively improves the cycling stability of the Zn anode. This review comprehensively summarizes the reaction mechanisms of interfacial modification for inhibiting the growth of Zn dendrites and the occurrence of side reactions. In addition, the research progress of interfacial engineering strategies for RAZIBs is summarized and classified. Finally, prospects and suggestions are provided for the design of highly reversible Zn anodes.

Synergistic Catalysis of SnO2/Reduced Graphene Oxide for VO2+/VO2+ and V2+/V3+ Redox Reactions.

In spite of their low cost, high activity, and diversity, metal oxide catalysts have not been widely applied in vanadium redox reactions due to their poor conductivity and low surface area. Herein, SnO2/reduced graphene oxide (SnO2/rGO) composite was prepared by a sol-gel method followed by high-temperature carbonization. SnO2/rGO shows better electrochemical catalysis for both redox reactions of VO2+/VO2+ and V2+/V3+ couples as compared to SnO2 and graphene oxide. This is attributed to the fact that reduced graphene oxide is employed as carbon support featuring excellent conductivity and a large surface area, which offers fast electron transfer and a large reaction place towards vanadium redox reaction. Moreover, SnO2 has excellent electrochemical activity and wettability, which also boost the electrochemical kinetics of redox reaction. In brief, the electrochemical properties for vanadium redox reactions are boosted in terms of diffusion, charge transfer, and electron transport processes systematically. Next, SnO2/rGO can increase the energy storage performance of cells, including higher discharge electrolyte utilization and lower electrochemical polarization. At 150 mA cm-2, the energy efficiency of a modified cell is 69.8%, which is increased by 5.7% compared with a pristine one. This work provides a promising method to develop composite catalysts of carbon materials and metal oxide for vanadium redox reactions.

Enhanced Catalysis of P-doped SnO2 for the V2+/V3+ Redox Reaction in Vanadium Redox Flow Battery.

In this work, nanosized P-doped SnO2 (SnO2-P) was prepared by a sol-gel method as a catalyst for the V3+/V2+ redox reaction in vanadium redox flow battery. Compared with SnO2, the electrochemical performance of SnO2-P is significantly improved. This is because P doping provides more active sites and shows greatly improved electrical conductivity, thereby increasing the electron transfer rate. As a result, SnO2-P shows better catalytic performance than SnO2. The SnO2-P modified cell is designed, and it exhibits an increase of 47.2 mA h in discharge capacity and 8.7% in energy efficiency compared with the pristine cell at 150 mA cm-2. These increases indicate that the modified cell has a higher electrolyte utilization rate. This study shows that SnO2-P is a new and efficient catalyst for vanadium redox flow battery.

Synergistic Catalysis of SnO2-CNTs Composite for VO 2 + /VO2+ and V2+/V3+ Redox Reactions.

In this study, a SnO2-carbon nanotube (SnO2-CNT) composite as a catalyst for vanadium redox flow battery (VRFB) was prepared using a sol-gel method. The effects of this composite on the electrochemical performance of VO 2 + /VO2+, and on the V2+/V3+ redox reactions and VRFB performance were investigated. The SnO2-CNT composite has better catalytic activity than pure SnO2 and CNT due to the synergistic catalysis of SnO2 and the CNT. SnO2 mainly provides the catalytic active sites and the CNTs mainly provide the three-dimensional structure and high electrical conductivity. Therefore, the SnO2-CNT composite has a larger specific surface area and an excellent synergistic catalytic performance. For cell performance, it was found that the SnO2-CNT cell shows a greater discharge capacity and energy efficiency. In particular, at 150 mA cm-2, the discharge capacity of the SnO2-CNT cell is 28.6 mAh higher than that of the pristine cell. The energy efficiency of the modified cell (7%) is 7.2% higher than that of the pristine cell (62.8%). This study shows that the SnO2-CNT is an efficient and promising catalyst for VRFB.

A hafnium oxide-coated dendrite-free zinc anode for rechargeable aqueous zinc-ion batteries.

In aqueous zinc-ion batteries, metallic zinc is widely used as an anode because of its non-toxicity, environmental benignity, low cost, high abundance and theoretical capacity. However, growth of zinc dendrites, corrosion of zinc anode, passivation, and occurrence of side reactions during continuous charge-discharge cycling hinder development of zinc-ion batteries. In this study, a simple strategy involving application of a HfO2 coating was used to guide uniform deposition of Zn2+ to suppress formation of zinc dendrites. The HfO2-coated zinc anode improves electrochemical performance compared with bare Zn anode. Therefore, for zinc-zinc symmetric cells, zinc anode with HfO2 coating (48 mV) shows lower voltage hysteresis than that of bare Zn anode (63 mV) at a current density of 0.4 mA cm-2. Moreover, cell with HfO2 coating also shows good cycling performance in Zn-MnO2 full cells. At a constant current density of 1.0 A g-1, discharge capacity of bare Zn-MnO2 full cell is only 37.9 mAh g-1 after 500 cycles, while that of Zn@HfO2-MnO2 full cell is up to 78.3 mAh g-1. This good electrochemical performance may be the result of confinement effect and reduction of side reactions. Overall, a simple and beneficial strategy for future development of rechargeable aqueous zinc-ion batteries is provided.

Anode Materials for Aqueous Zinc Ion Batteries: Mechanisms, Properties, and Perspectives.

Aqueous Zn-ion batteries (ZIBs) are promising safe energy storage systems that have received considerable attention in recent years. Based on the electrochemical behavior of Zn2+ in the charging and discharging process, herein we review the research progress on anode materials for use in aqueous ZIBs based on two aspects: Zn deposition and Zn2+ intercalation. To date, Zn dendrite, corrosion, and passivation issues have restricted the development of aqueous ZIBs. However, many strategies have been developed, including structural design, interface protection of the Zn anode, Zn alloying, and using polymer electrolytes. The main aim is to stabilize the Zn stripping/plating layer and limit side reactions. Zn2+-intercalated anodes, with a high Zn2+ storage capacity to replace the current metal Zn anode, are also a potential option. Finally, some suggestions have been put forward for the subsequent optimization strategy, which are expected to promote further development of aqueous ZIBs.

One-step activation of high-graphitization N-doped porous biomass carbon as advanced catalyst for vanadium redox flow battery.

In this paper, we reported a one-step activation strategy to prepare highly graphitized N-doped porous carbon materials (KDC-FAC) derived from biomass, and adopted ferric ammonium citrate (FAC) as active agent. At high temperature, FAC was decomposed into Fe- and NH3-based materials, further increasing graphitization degree, introducing N-containing functional groups and forming porous structure. KDC-FAC has superior electrocatalytic activity and stability towards V2+/V3+ and VO2+/VO2+ redox reactions. High graphitization degree can enhance the conductivity of carbon material, and porous structure is conducive to increase reaction area of vanadium redox couples. Moreover, N-containing functional groups are beneficial to improve the electrode wettability and serve as active sites. The single cell tests demonstrate that KDC-FAC modified cell exhibits good adaptability under high current density and superb stability in cycling test. Compared with pristine cell, the energy efficiency of KDC-FAC modified cell is increased by 9% at 150 mA cm-2. This biomass-derived carbon-based material proposed in our work is expected to be an excellent catalyst for vanadium redox flow battery.