Zinc Triflate Research Articles

Anion-induced optimization of non-aqueous zinc-air battery performance: Insights into OTF− selection

Rechargeable non-alkaline zinc-air batteries (ZABs) address the CO₂ incompatibility and instability issues of conventional alkaline batteries. However, the impact of solid discharge products like zinc oxide on discharge capacity at the air cathode remains unexplored. In this study, we investigate how anions influence ion pair solvation structures using Zinc trifluoromethanesulfonate (Zn(OTF)₂)-N, N-dimethylformamide (DMF) and Zinc acetate (Zn(Ac)₂)-DMF electrolytes, and how these structures affect the distribution of discharge product. Our finding shows that anions with lower donor numbers (DNs), like the weaker ligand OTF- (20.5), enhance the zinc ion activity and promote rapid Zn2⁺ reactions with oxygen during discharge, leading to a more than tenfold increase in discharge capacity. In contrast, acetate anions with higher DNs (43.3) form stable complexes, inhibiting zinc ion activity and causing the formation of film-like discharge products, which reduces ZAB performance. The Zn(OTF)₂-DMF electrolyte also enables a battery lifespan of over 200 h, more than fivefold compared to the acetate-based system.

Optimizing Aqueous Zinc-Sulfur Battery Performance via Regulating Acetonitrile Co-Solvents and Carbon Nanotube Carriers.

Rechargeable aqueous zinc-sulfur batteries (AZSBs) are gaining attention due to their high energy density, ultra-stable discharge platform, and safety. However, poor liquid/solid reaction processes at the anode and cathode reduce reaction kinetics, and the severe dissolution of polysulfides causes shuttle effects during discharge/charge cycles, hindering practical applications. Improving performance requires optimizing both the cathode and electrolyte. Herein, we design an organic-inorganic hybrid electrolyte (zinc trifluoromethanesulfonate and trace iodine monomer dissolved in an acetonitrile/water co-solvent (AN-X)) and a partially exfoliated multi-walled carbon nanotube (PECNT) hosted sulfur (S@PECNTs) cathode for AZSBs. The sulfur is highly dispersed along the PECNTs with appropriate wettability at the electrode/electrolyte interface using AN-3 as the electrolyte. Meanwhile, this electrolyte inhibits hydrogen evolution at negative potentials and promotes uniform Zn ion stripping/plating. Expressively, the AN-3-based AZSB exhibits a high discharge capacity of 1370 mAh g-1 with excellent Coulombic efficiency (79.9%), outstanding rate capability, and cycling performance. These improvements are attributed to the synergistic effect between the S@PECNTs and the AN-3 electrolyte, which reduces Rct to enhance reaction kinetics and blocks the dissolution and shuttle effect of polysulfides, ensuring a reversible reaction between zinc and sulfur.

A Rechargeable “Rocking Chair” Type Zn−CO2 Battery

AbstractRising global temperatures and critical energy shortages have spurred researches into CO2 fixation and conversion within the realm of energy storage such as Zn−CO2 batteries. However, traditional Zn−CO2 batteries employ double‐compartment electrolytic cells with separate carriers for catholytes and anolytes, diverging from the “rocking chair” battery mechanism. The specific energy of these conventional batteries is constrained by the solubility of discharge reactants/products in the electrolyte. Additionally, H2O molecules tend to trigger parasitic reactions at the electrolyte/electrode interfaces, undermining the long‐term stability of Zn anodes. In this report, we introduce an innovative “rocking chair” type Zn−CO2 battery that utilizes a weak‐acidic zinc trifluoromethanesulfonate aqueous electrolyte compatible with both cathode and anode. This design minimizes side reactions on the Zn surface and leverages the high catalytic activity of the cathode material, allowing the battery to achieve a substantial discharge capacity of 6734 mAh g−1 and maintain performance over 65 cycles. Moreover, the successful production of pouch cells demonstrates the practical applicability of Zn−CO2 batteries. Electrode characterizations confirm superior electrochemical reversibility, facilitated by solid discharge products of ZnCO3 and C. This work advances a “rocking chair” Zn−CO2 battery with an enhanced specific energy and a reversible pathway, providing a foundation for developing high‐performance metal‐CO2 batteries.

Homogeneous Zn(II) salts as efficient Lewis acid catalysts for the esterification of levulinic acid with diols

The valorization of renewable feedstocks to produce biochemicals and biofuels is an essential focus of contemporary research, with non-food crop biomass emerging as a cost-effective and environmentally friendly option. Among the chemicals derived from lignocellulosic biomass, levulinic acid (LAH) is a notable chemical platform due to its versatile applications. This study investigates the eco-friendly esterification of levulinic acid with polyols, catalyzed by zinc(II) species under mild, solvent-free conditions.A comprehensive screening of various zinc(II) species was conducted, to identify the most effective catalyst, ultimately selecting zinc triflate for its performance. The esterification scope was extended to three diols: 1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol. These esters can replace fossil-based chemicals in many emerging sectors, as lubricants and as components in energy storage devices. The reaction conditions were fine-tuned to maximize yield and selectivity, using NMR spectroscopy to monitor the formation of mono- and di-esters and assess reaction profiles. Optimization experiments demonstrated that a catalyst loading of 1.0 %mol and a temperature of 120 °C yielded quantitative conversion within convenient reaction time (2–4 h). The findings highlight the efficiency of simple zinc(II) catalysts in producing levulinate esters with high yields and selectivity under sustainable conditions. Therefore, this research contributes to the development of greener processes to produce valuable chemicals and additives from renewable resources.

Atomic Level‐Macroscopic Structure‐Activity of Inhomogeneous Localized Aggregates Enabled Ultra‐Low Temperature Hybrid Aqueous Batteries

The utilization of hybrid aqueous electrolytes has significantly broadened the electrochemical and temperature ranges of aqueous batteries, such as aqueous zinc and lithium‐ion batteries, but the design principles for extreme operating conditions remain poorly understood. Here, we systematically unveil the ternary interaction involving salt‐water‐organic co‐solvents and its intricate impacts on both the atomic‐level and macroscopic structural features of the hybrid electrolytes. This highlights a distinct category of micelle‐like structure electrolytes featuring organic‐enriched phases and nanosized aqueous electrolyte aggregates, enabled by appropriate low donor number co‐solvents and amphiphilic anions. Remarkably, the electrolyte enables exceptional high solubility, accommodating up to 29.8 m zinc triflate within aqueous micelles. This configuration maintains an intra‐micellar salt‐in‐water setup, allowing for a broad electrochemical window (up to 3.86 V), low viscosity, and state‐of‐the‐art ultralow‐temperature zinc ion conductivity (1.58 mS cm−1 at –80°C). Building upon the unique nature of the inhomogeneous localized aggregates, this micelle‐like electrolyte facilitates dendrite‐free Zn plating/stripping, even at –80°C. The assembled Zn||PANI battery showcases an impressive capacity of 71.8 mAh g−1 and an extended lifespan of over 3000 cycles at −80°C. This study opens up a promising approach in electrolyte design that transcends conventional local atomic solvation structures, broadening the water‐in‐salt electrolyte concept.

Atomic Level-Macroscopic Structure-Activity of Inhomogeneous Localized Aggregates Enabled Ultra-Low Temperature Hybrid Aqueous Batteries.

The utilization of hybrid aqueous electrolytes has significantly broadened the electrochemical and temperature ranges of aqueous batteries, such as aqueous zinc and lithium-ion batteries, but the design principles for extreme operating conditions remain poorly understood. Here, we systematically unveil the ternary interaction involving salt-water-organic co-solvents and its intricate impacts on both the atomic-level and macroscopic structural features of the hybrid electrolytes. This highlights a distinct category of micelle-like structure electrolytes featuring organic-enriched phases and nanosized aqueous electrolyte aggregates, enabled by appropriate low donor number co-solvents and amphiphilic anions. Remarkably, the electrolyte enables exceptional high solubility, accommodating up to 29.8 m zinc triflate within aqueous micelles. This configuration maintains an intra-micellar salt-in-water setup, allowing for a broad electrochemical window (up to 3.86 V), low viscosity, and state-of-the-art ultralow-temperature zinc ion conductivity (1.58 mS cm-1 at -80 °C). Building upon the unique nature of the inhomogeneous localized aggregates, this micelle-like electrolyte facilitates dendrite-free Zn plating/stripping, even at -80 °C. The assembled Zn||PANI battery showcases an impressive capacity of 71.8 mAh g-1 and an extended lifespan of over 3000 cycles at -80 °C. This study opens up a promising approach in electrolyte design that transcends conventional local atomic solvation structures, broadening the water-in-salt electrolyte concept.

Rechargeable zinc-water battery for sustainable hydrogen generation

Metal-water primary batteries hold promise for distributed hydrogen production but suffer from limited renewability of metal electrodes in aqueous electrolytes. Here, we introduce a novel concept of a rechargeable zinc-water battery featuring a reversible zinc anode paired with a bifunctional water electrolysis electrode, realized in a specially designed aqueous electrolyte-a mild zinc triflate aqueous electrolyte with the addition of ethylenediaminetetraacetic acid disodium (EDTANa2). The system enables high-purity hydrogen production during discharge and high-purity oxygen production during charge in a membrane-free setup. In the zinc-water battery, EDTANa2 enhances the water-splitting electrode's performance by replacing hydrophobic OTF- anions, ensuring optimal water activity. Additionally, EDTANa2 enhances Zn electrode reversibility by chelating Zn2+, preventing solvated water decomposition during zinc deposition. This integrated battery continuously undergoes charge-discharge cycles for over 55 h at a current density of 6 mA cm-2. Moreover, it achieves a high hydrogen evolution rate of 12.5 mL cm-2 h-1, enabling cost-effective, high-purity hydrogen production without expensive membranes. These findings open new avenues for sustainable hydrogen generation and energy storage in nano energy systems.

Diethylene glycol reduced the water activity of aqueous electrolyte via regulating interphase chemistry for highly durable Zinc-ion batteries

The uncontrollable dendrite growth and parasitic side reactions of Zn lead to poor cycling stability, hindering the practical application of aqueous zinc-ion batteries. Here, we develop a new hybrid electrolyte with zinc trifluoromethanesulfonate dissolved in water and co-solvent diethylene glycol (DEG). DEG can not only alter the Zn2+ solvation structure with the co-participation of DEG and anion to reduce active water molecules, but also interrupt the hydrogen-bond network of the original water. DEG is more easily absorbed on Zn surface than H2O to regulate electric double layer. Based on these unique effects, DEG can regulate interface chemistry, forming a robust solid electrolyte interphase and adjusting Zn2+ stripping/plating behaviors, which suppress side reactions and dendrite growth. Their synergetic effect results in the great improved cycling stability of Zn anode with 5000 h in symmetric cell at 1 mA cm−2 and 1 mAh cm−2. The work shed light on the design of high-performance aqueous electrolyte to advance zinc-ion batteries.

Model-based electrolyte design for near-neutral aqueous zinc batteries with manganese-oxide cathodes

Most modern zinc-ion batteries (ZIBs) with MnO2 cathodes utilize near-neutral aqueous electrolytes based on a zinc sulfate (ZnSO4) salt. They achieve good cycling stabilities with high intrinsic safety, employ environmentally friendly materials, and deliver competitive volumetric energy densities. However, the limited solubility of zinc-sulfate species influences the performance and cycling mechanism of these cells. We examine the speciation and solubility limits of ZnSO4, zinc chloride (ZnCl2), and zinc triflate (Zn(CF3SO3)2) in aqueous solutions and simulate their intrinsic transport properties. We use our earlier developed and validated full-cell model to investigate the effects of several electrolytes on the two-phase cycling behavior. Previously, we reported that the origin of the second phase is based on an interaction mechanism between cathodic dissolution and a precipitation reaction at the cathode. We investigate this interplay between electrolyte stability and cathodic dissolution based on electrolyte choice. Our theory-based approach allows us to identify performance indicators of aqueous electrolytes and draws a consistent pathway to optimize electrolyte design for manganese-based ZIBs.

Modulation of zinc deposition behaviour by electrostatically spun PAN-ZnTFSI fibre layer on separator for aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) are well-suited for current energy storage technologies due to their high safety and low cost. However, battery failures resulting from dendrites and side reactions restrict their widespread application. Here, we designed a polyacrylonitrile (PAN)-zinc trifluoromethanesulfonate (ZnTFSI) nanofibre synergistic glass fibre (PZ-GF) to modulate the interfacial deposition kinetics. The effective coordination of numerous CN functional groups within PZ, in conjunction with Zn2+, results in the homogeneous dispersion of the electric field across the electrode, which promotes the uniform deposition of Zn2+ on the zinc anode and thus significantly inhibits the rapid growth of zinc dendrites. ZnTFSI is hydrophilic and has strong hydrogen bonding interactions with the H2O molecule so that the separator can be used as a molecular sieve to regulate the flux of H2O, promote the desolvation of hydrated zinc ions, and inhibit side reactions.Tests of the initial nucleation overpotential of the symmetric battery and calculation of the activation energy reflect that PZ-GF has a smaller nucleation energy barrier and enhanced kinetic effect. And the zinc symmetric battery with PZ-GF film shows an ultra-long cycle stability of 1200 cycles with a capacity retention of 75 % even at 0.5 A g−1 for the Zn//VO2 full cells.

The Role of Zinc Triflate Additive for Improved Electrochemical Performance of Nickel-Rich Layered Oxide Lithium Battery Cathode via Suppression of Interfacial Parasitic Reactions

Nickel-rich layered oxide cathode materials with low cobalt content, such as LiNi0.90Mn0.05Co0.05O2 (NMC90), have the potential to enable cost-effective, high-energy-density lithium-metal batteries. However, NMC90 cathode materials are prone to severe parasitic reactions at higher voltages during prolonged cycling. The addition of small percentages of electrolyte additives to the neat commercial electrolyte can significantly enhance the overall electrochemical performance of lithium-metal batteries. This study investigates the effects of zinc triflate (Zn(Otf)2) as an electrolyte additive on the enhancement of the electrochemical performances of lithium-metal batteries comprising nickel-rich layered oxide cathode materials. X-ray photoelectron spectroscopy analysis revealed that Zn(Otf)2 decomposition leads to enhanced fluorination at the interfacial layers, which contributes to improved chemical stability. Utilizing operando electrochemical mass spectroscopy, we demonstrate that Zn(Otf)2 additives effectively suppress the electrolyte degradation, which is otherwise detrimental to electrochemical performance. Electrochemical studies show that the inclusion of only ∼1% Zn(Otf)2 as additive in neat commercial electrolyte enhances the electrochemical performance indicated by a 10% improvement in discharge capacity after 150 cycles. This study paves the way for researchers to develop novel fluorinated triflate based electrolyte additives aimed at enhancing the stabilization of interfaces for lithium ion, and potentially also Li-metal batteries.

Multifunctional Dual‐Metal‐Salt Derived Ternary Eutectic Electrolyte for Highly Reversible Zinc Ion Battery

AbstractDeep eutectic electrolytes offer opportunities for tailoring solvation structure and interface chemistry in advanced batteries, but developing deep eutectic electrolytes for high‐performance zinc ion batteries (ZIBs) remains a challenge. Herein, multifunctional dual‐metal‐salt derived ternary eutectic electrolytes (DMEEs) are designed via a supporting salt strategy for dendrite‐free and long‐lifespan ZIBs. DMEEs are constructed by zinc trifluoromethanesulfonate (Zn(OTF)2), supporting salt of lithium bis(trifluoromethanesulfonyl)imide, and neutral ligand of N‐methylacetamide. Noticeably, supporting salt with weak lattice energy not only induces the reconstruction of intermolecular interactions to form ion pairs and ion aggregates but also tailors the Zn2+ solvation structure and solid electrolyte interface (SEI). The developed DMEEs possess a dual‐anion‐rich Zn2+ solvation shell and induce an inorganic‐rich hybrid SEI, which effectively suppresses side reactions and obtains a dendrite‐free Zn anode with high reversibility. Remarkably, Zn//Zn cells demonstrate cycling stability for over 3000 h, and Zn//PANI full cells deliver no significant capacity decay after 5000 cycles at a high current density of 5 A g−1. This work opens a new avenue to design advanced deep eutectic electrolytes, and the deep understanding of solvation structure and SEI offers guidelines for developing high‐performance batteries.

Ti3C2Tx Filled in EMIMBF4 Semi-Solid Polymer Electrolytes for the Zinc-Metal Battery.

Zinc-ion batteries (ZIBs) are promising candidates for safe energy storage applications. However, undesirable parasitic reactions such as dendrite growth, gas evaluation, anode corrosion, and structural damage to the cathode under an acidic microenvironment severely affected cell performance. To resolve these issues, an MXene entrapped in an ionic liquid semi-solid gel polymer electrolyte (GPE) composite was explored. The molecular-level mixing of poly(vinylidene fluoride-co-hexafluoropropylene) (PVHF), zinc trifluoromethanesulfonate (Zn(OTF)2), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) ionic liquid, and Ti3C2Tx MXene provided a controlled Zn2+ shuttle toward the anode/cathode. Ti3C2Tx/EMIBF4/Zn(OTF)2/PVHF exhibited a breaking strength of 0.36 MPa with an associated extension of 23%. The Zn//Ti3C2Tx/EMIBF4/Zn(OTF)2/PVHF//Zn symmetric cell with continuous zinc plating/stripping exhibited excellent Zn2+ ion mobility toward the anode and cathode without undesired reactions. This was confirmed by post-mortem analysis after a symmetric cell compatibility test. The as-prepared GPE with a Na3V2(PO4)3 (NVP) cathode exhibited a high chemical diffusion coefficient of 1.14 × 10-7. It also showed an outstanding reversible capacity of 89 mAh g-1 at C/10 with an average discharge plateau voltage of 1.45 V, cycle durability, and controlled self-discharge. These results suggested that the Zn2+ ions in the Ti3C2Tx/EMIBF4/Zn(OTF)2/PVHF composite are reversibly labile in the anode and cathode directions.

Crosslinking of polyethylene with polysilsesquioxane via carbamate linkages: Synthesis, shape recovery, and reprocessing properties

AbstractIn this contribution, we reported the crosslinking of polyethylene (PE) with dynamic silyl ether bonds. First, polycyclooctene copolymers bearing hydroxyl groups were synthesized via the ring‐opening metathesis copolymerization of cyclooctene with 5‐norbornene‐2‐methanol. The hydroxy‐functionalized polycyclooctene copolymers were further hydrogenated into the corresponding hydroxy‐functionalized PE copolymers. The PE copolymers were allowed to react with 3‐isocyanatopropyltriethoxysilane to obtain the PE copolymers bearing triethoxysilane groups. By taking advantage of hydrolysis and condensation of triethoxysilane groups grafted onto PE chains, the PE copolymers were well crosslinked; polysilsesquioxane (PSSQ) segments behaved as the crosslinking linkages in the networks. Notably, the PE networks were reprocessable (or recyclable) while zinc trifluoromethanesulfonate [Zn(OTf)2] was incorporated. The reprocessing properties of the PE networks were quite dependent on the crosslinking densities. The reprocessing behavior of the networks is attributable to the introduction of two dynamic chemistries: (i) the metathesis of silyl ether bonds which was catalyzed with Zn(OTf)2 and (ii) transcarbamoylation of carbamates which was catalyzed with dibutyltin dilaurate. Owing to the crosslinking, the PE networks displayed excellent shape memory properties. For the shape memory networks, notably, the original shapes can be reprogrammed with the aid of the exchange of the dynamic covalent bonds introduced into the systems.

Cooperative Covalent–Noncovalent Organocatalysis of the Knoevenagel Condensation Based on an Amine and Iodonium Salt Mixture

AbstractThe experimentally obtained kinetic data has indicated the existence of a synergetic cocatalytic effect provided by an iodonium salt in the base‐catalyzed Knoevenagel condensation. The diphenyliodonium triflate serving as the halogen bond‐donating Lewis acid provides the higher cocatalytic effect than zinc(II) triflate or triflic acid serving, respectively, as the metal cation‐based Lewis acid and Brønsted acid. Such a cocatalytic effect remains the same for a broad scope of carbonyl compounds covering aldehydes featuring electron‐withdrawing or electron‐donating substituents, as well as ketone involved in the reaction.

Iodide manipulation using zinc additives for efficient perovskite solar minimodules

Interstitial iodides are the most critical type of defects in perovskite solar cells that limits efficiency and stability. They can be generated during solution, film, and device processing, further accelerating degradation. Herein, we find that introducing a small amount of a zinc salt- zinc trifluoromethane sulfonate (Zn(OOSCF3)2) in the perovskite solution can control the iodide defects in resultant perovskites ink and films. CF3SOO̶ vigorously suppresses molecular iodine formation in the perovskites by reducing it to iodide. At the same time, zinc cations can precipitate excess iodide by forming a Zn-Amine complex so that the iodide interstitials in the resultant perovskite films can be suppressed. The perovskite films using these additives show improved photoluminescence quantum efficiency and reduce deep trap density, despite zinc cations reducing the perovskite grain size and iodide interstitials. The zinc additives facilitate the formation of more uniform perovskite films on large-area substrates (78-108 cm2) in the blade-coating process. Fabricated minimodules show power conversion efficiencies of 19.60% and 19.21% with aperture areas of 84 and 108 cm2, respectively, as certified by National Renewable Energy Laboratory (NREL), the highest efficiency certified for minimodules of these sizes.

Use of Polyacrylonitrile as Anodic Artificial Solid Electrolyte Interphase for Aqueous-Based Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted attention for energy storage systems because of their high specific capacity, low cost, and safety. However, practical application of the zinc anode in mild acidic electrolytes is limited by several issues such as dendrite formation, corrosion, hydrogen evolution reaction, passivation and relatively low cycling performance. Coating the zinc anode with graphite (GP) can partially solve these issues and improves the cycling performance of ZIB. However, after long-term charge/discharge cycles, zinc tends to migrate and redeposit over the surface of GP owing to the electronic conductivity of GP particles. Thus, after long-term cycling, the issues mentioned are back. Fabrication of artificial solid electrolyte interphase (ASEI) on the surface of the zinc anode shows high potential for solving these issues. In this work, polyacrylonitrile (PAN) with zinc trifluoromethanesulfonate (Zn(CF3SO3)2) (PANZ) as ASEI was coated on the GP layer onto the zinc anode (PANZ@GP@Zn), and compared with the anode having GP coated layers and pristine zinc anode. The coating layer was prepared by the doctor blading method. The result showed that the PANZ@GP@Zn anode can reduce zinc deposition over the anode surface when compared with the GP@Zn anode, leading to the high cycling stability of ZIBs and extending the battery's life.

Preparation of an aqueous zinc ion rGH/V2O5 photorechargeable supercapacitor.

A photorechargeable supercapacitor was constructed using vanadium pentoxide (V2O5), reduced graphene oxide hydrogel (rGH), and zinc trifluoromethanesulfonate (Zn(CF3SO3)2) as the photoanode, cathode, and electrolyte, respectively. The phase composition, microstructure, chemical structure, light absorption, and specific surface area of the synthesized products and the electrochemical performance of the rGH/V2O5 supercapacitor were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV-Vis spectroscopy, the Brunauer-Emmett-Teller (BET) method, and an electrochemical workstation, respectively. The results show that the device has a specific capacity of 164 F g-1 at 0.5 A g-1 under illumination with 95 mW cm-2 light intensity, which is 20.5% higher than that under normal electrical charging. The supercapacitor has a 75% capacity retention rate and 100% coulombic efficiency, respectively, after 10 000 testing cycles under photoelectric synergistic charging and discharging. The as-constructed rGH/V2O5 photorechargeable supercapacitor exhibits promising application potential in electric vehicles and wearable electronics.

Sustainable supercapacitor with a natural rubber‐based electrolyte and natural graphite‐based electrodes

AbstractSupercapacitors are at the forefront of energy storage devices due to their ability to fulfill quick power requirements. However, safety and cost are important parameters for their real‐world applications. Green materials‐based electrodes and electrolytes can make them safer and cost‐effective. Herein, a supercapacitor based on a methyl‐grafted natural rubber/salt‐based electrolyte and natural graphite (NG)‐based electrodes are fabricated and characterized. Zinc trifluoromethanesulfonate [Zn(CF3SO3)2] is used as the salt for the electrolyte. A mixture of NG, activated charcoal, and polyvinylidenefluoride is used for electrodes. Our supercapacitor shows a single electrode specific capacitance, Csc of 4.2 Fg−1 from impedance measurement. Moreover, the capacitive and resistive features are dominant at low and high frequencies, respectively. The cyclic voltammetry test shows the dependence of Csc on the scan rate with a high value at slow scan rates. Performance of the supercapacitor during 5000 charge and discharge cycles at a constant current of 90 μA shows a rapid decrease of single electrode specific discharge capacitance at the beginning, but it starts to stabilize after about 2500 cycles. These findings are relevant to further developments of green materials‐based supercapacitors, offering opportunities to expand the functionalities of supercapacitors in green technologies.

Bistate-type ion storage of azo polymer for aqueous zinc ion battery

Azo organic molecules are emerging as promising electrode candidates for energy storage systems due to their high theoretical specific capacity and excellent kinetic performance. In general perception, conventional azo organic small molecules used as cathode material in aqueous batteries remain a challenge because of the poor cycling stability in aqueous electrolytes. Herein, azo organic polymers (AOPs) were synthesized using a diazo-coupling reaction under mild conditions and developed as cathode materials for aqueous zinc-ion batteries. Owing to the long conjugate structure, the AOPs afford extra-long stability with outstanding cyclability of >1000 cycles at 2 A g−1, a comparable capacity (170 mAh g−1 at 0.5 A g−1), and excellent rate performance from 0.5 g−1 to 10 A g−1 in aqueous electrolytes. Significantly, the hydroxyl oxygen and azo functional groups on AOPs can spontaneously form metal heterocyclic complexes with zinc ions in 1 M Zinc trifluoromethanesulfonate (Zn(OTF)2) electrolyte, leading to a notable increase in voltage (by 0.2 V) and capacity (by 43 mAh g−1 at a current density of 2 A g−1) in aqueous zinc-ion battery. Additionally, mechanistic analysis reveals that the AOPs are an active material for bistate storage of zinc ions during the charging and discharging process. The AOPs not only store zinc ions in fully charged state by forming metal heterocyclic complexes but also store zinc ions by a redox reaction between azo functional groups and zinc ions at the discharge process. The results put forward a novel storage mechanism for zinc ions and will pave the way for AOPs’ development in aqueous batteries.