Iodine Redox Research Articles

Photo‐Assisted Zn‐Iodine Battery via Bifunctional Cathode with Iodine Host and Solar Response Boost

AbstractThe aqueous photo‐assisted battery is considered an efficient means of converting and storing solar energy in one device. However, identifying a suitable photocathode with excellent iodine capture capabilities for photo‐assisted Zn‐iodine batteries still remains challenging. In this work, bifunctional BiOI is prepared as sole cathode material for a photo‐assisted Zn‐iodine battery while simultaneously realizing an iodine host and solar responsiveness. The as‐presented BiOI with abundant vacancies offers highly reversible photo‐assisted iodine redox reactions. Meanwhile, the dual reaction routes involving vacancy iodine storage and reversible two‐steps iodine redox are confirmed by in/ex situ characterization techniques during the energy storage process. Consequently, the assembled battery exhibits areal capacity of 0.24 mAh cm−2 at 1 mA cm−2 with coulombic efficiency exceeding 96.5%. More impressively, benefiting from the wide visible light absorption of the BiOI cathode, the battery demonstrates a much enhanced specific areal capacity of 0.4 mAh cm−2 at 1 mA cm−2 under sun illumination, representing a remarkable increment of 60% compared to that in the dark environment. This work expands the utility of cathode materials for a photo‐assisted Zn‐iodine battery.

Strong adsorption Fe[sbnd]N[sbnd]C catalytic cathode for 50,000 cycles aqueous zinc-iodine batteries

Aqueous zinc-iodine batteries have garnered increasing attention due to their low cost and high safety. However, their practical application is impeded by sluggish iodine redox reaction kinetics and the “shuttle effect” of polyiodides, which result in poor rate performance and limited cycled life. Here, we developed N-doped porous carbon fiber derived from Prussian blue and polyacrylonitrile (PAN) as a self-supporting cathode material for zinc-iodine batteries. The material demonstrates a high iodine adsorption capacity in the electrolyte solution. Density Function Theory (DFT) calculations indicate that the prepared materials demonstrate good catalytic activity. Furthermore, the interconnected carbon fiber network, characterized by high conductivity and a large specific surface area, facilitates rapid electron transport and ion diffusion. Consequently, the zinc-iodine battery demonstrates outstanding rate performance (148mAh g−1 at a high current density of 10 A/g) and a long cycling life of 50,000 cycles, with a capacity retention rate of 72.1 %. Additionally, the battery achieves an impressive calendar life of 8 months and 23 days.

Thermodynamically and Dynamically Boosted Electrocatalytic Iodine Conversion with Hydroxyl Groups for High-Efficiency Zinc-Iodine Batteries.

Rechargeable zinc-iodine (Zn-I2) batteries have shown immense potential for grid-scale energy storage applications, but there remain challenges of improving efficiency and cycling stability due to the sluggish iodine reduction reaction (IRR) kinetics and serious shuttle problem of polyiodides. We herein demonstrate an efficient metal-free hydroxyl (-OH)-functionalized carbon catalyst that effectively boosts the performance of Zn-I2 batteries. It has been found that the obtained electrocatalytic performance is strongly correlated with the surface oxygen chemical environment in the carbon matrix. Both theoretical calculations and experimental measurements have uncovered that the -OH group, rather than carbonyl (-C═O) and carboxyl (-COOH), provides the active electrocatalytic site for IRR, improves the iodine redox kinetics and the electrochemical reversibility, and facilitates I2 nucleation. As confirmed by a series of in situ and ex situ spectroscopy techniques, due to the favorable reaction thermodynamics and the lowered energy barrier for I3- dissociation, the O-H···I channels can effectively trigger the direct transformation of I2/I- and avoid the formation of stable polyiodides. As a result, the as-assembled battery of I2/oxygen-functionalized carbon cloth (I2/OCC-2)//Zn exhibits a high capacity of 2.27 mA h cm-2 at 1 mA cm-2, outstanding rate capability with 89.0% capacity retention at 20 mA cm-2, and long-term stability of 10,000 cycles.

Redox mediator enabling fast reaction kinetics and high utilization of iodine in aqueous iodine redox flow battery

Aqueous iodine redox flow batteries (AIRFBs) have been identified as a promising technology for large-scale energy storage. However, practical capacity of AIRFBs is limited by the relatively low utilization of iodine caused by the low reaction kinetics. Here, we report an electrode modified by cobalt hexacyanoferrate (CoHCF), which supports a redox-mediating process developing alternative redox reaction pathways of iodine with reduced redox activation energies. Contributed by the strong adsorption of iodine by CoHCF, redox reaction kinetics of iodine species is accelerated, and the utilization of iodine in batteries is increased. Applying the CoHCF modified carbon felt as cathode electrode, the constructed zinc-iodine redox flow battery exhibits a high iodine utilization reaching 95.59% of the theoretical capacity at a current density of 20 mA cm−2, which enhances 139.89% comparing to the battery without electrode modification. The redox mediator-based electrode enabling fast reaction kinetics and high utilization of iodine species offers a promising strategy enhancing the battery performance thereby advancing the development of AIRFBs.

Integrated Trap‐Adsorption‐Catalysis Nanoreactor for Shuttle‐Free Aqueous Zinc‐Iodide Batteries

AbstractAqueous zinc‐iodine batteries (AZIBs) are very promising energy storage systems owing to their safety, reliability, large specific capacity, and durable lifespan. However, the sluggish iodine redox kinetics and polyiodides shuttle effect severely impedes their wider application. Addressing these challenges, this study develops a new multifunctional nanoreactor integrating “Trap‐Adsorption‐Catalysis” advantages, which features the electron‐rich cobalt (Co) nanoparticles embedded in porous activated carbon (AC). Benefiting from the integrated advantages of trap‐adsorption‐catalysis behavior in the nanoreactor, this novel system enables the fast iodine (I2/I‐) conversion by enhanced kinetics, achieving high utilization of iodine and corrosion‐free zinc anode without producing polyiodides. In situ UV–vis spectroscopy, theoretical calculation combined with electrochemical analysis demonstrates that the Co@AC nanoreactor reduces the adsorption energy and conversion energy barrier of iodine species, and accelerates the conversion of polyiodides to improve the electrochemical properties. Notably, the Co@AC/I2 cathode delivers an outstanding rate capability of 221.1 and 102.5 mA h g−1 at the current density of 0.5 and 25C with high CE over >99.9%, respectively, low self‐discharge rate over 96h and high energy efficiency (EE) of 89.2% at 5.0C over 1000 cycles. These self‐discharge and EE properties are the best among AZIBs systems with Co‐based host cathodes ever reported.

Circumventing bottlenecks in H2O2 photosynthesis over carbon nitride with iodine redox chemistry and electric field effects

Artificial photosynthesis using carbon nitride (g-C3N4) holds a great promise for sustainable and cost-effective H2O2 production, but the high carrier recombination rate impedes its efficiency. To tackle this challenge, we propose an innovative method involving multispecies iodine mediators (I−/I3−) intercalation through a pre-photo-oxidation process using potassium iodide (suspected deteriorated “KI”) within the g-C3N4 framework. Moreover, we introduce an external electric field by incorporating cationic methyl viologen ions to establish an auxiliary electron transfer channel. Such a unique design drastically improves the separation of photo-generated carriers, achieving an impressive H2O2 production rate of 46.40 mmol g−1 h−1 under visible light irradiation, surpassing the most visible-light H2O2-producing systems. Combining various advanced characterization techniques elucidates the inner photocatalytic mechanism, and the application potential of this photocatalytic system is validated with various simulation scenarios. This work presents a significative strategy for preparing and applying highly efficient g-C3N4-based catalysts in photochemical H2O2 production.

Aqueous Rechargeable Manganese/Iodine Battery

AbstractCarbon neutralization has promoted the identification of new types of energy storage devices. Aqueous iodine batteries (AIBs) with reversible iodine redox activity are considered a viable candidate for stationary energy storage units and thus have recently drawn extensive research interest. Herein, we introduce an aqueous manganese iodine battery (AMIB), utilizing sodium iodide (NaI) as a redox‐active additive in the Mn(ClO4)2 (NMC) electrolyte, activated carbon (AC) as a redox host and Mn ions as the charge carrier. Taking advantage of enhanced kinetics facilitated by I2/2I− redox activity, our suggested AMIBs can be electrochemically charged/discharged with only a 6 % loss in capacity after 2,000 cycles at a low current density of 0.3 A g−1 in an AC||AC coin cell configuration. Moreover, the AC||Zn−Mn hybrid full‐cell configuration is also established with AC and a Zn−Mn anode involving the NMC electrolyte, which retains a high energy of 185 Wh kg−1 at a specific power of 2,600 W kg−1. Overall, the AMIBs in this study preferred I2/I− conversion chemistry, yielding stable cycle stability, rate performance, and low capacity loss per cycle when compared to Manganese Ion Batteries (MIBs) which are based on Mn2+ intercalation chemistry.

Ultrastable Electrolytic Zn-I2 Batteries Based on Nanocarbon Wrapped by Highly Efficient Single-Atom Fe-NC Iodine Catalysts.

Aqueous Zn-iodine (Zn-I2) conversion batteries with iodine redox chemistry suffers the severe polyiodide shuttling and sluggish redox kinetics, which impede the battery lifespan and rate capability. Herein, an ultrastable Zn-I2 battery is introduced based on single-atom Fe-N-C encapsulated high-surface-area carbon (HC@FeNC) as the core-shell cathode materials, which accelerate the I-/I3 -/I° conversion significantly. The robust chemical-physical interaction between polyiodides and Fe-N4 sites tightly binds the polyiodide ions and suppresses the polyiodide shuttling, thereby significantly enhancing the coulombic efficiency. As a result, the core-shell HC@FeNC cathode endows the electrolytic Zn-I2 battery with an excellent capacity, remarkable rate capability, and an ultralong lifespan over 60000 cycles. More importantly, a practical 253Wh kg-1 pouch cell shows good capacity retention of 84% after 100 cycles, underscoring its considerable potential for commercial Zn-I2 batteries.

Electron-outflowing heterostructure hosts for high-voltage aqueous zinc-iodine batteries

Enhancing the energy density is an imperative challenge in the advancement of aqueous zinc-iodine (Zn-I2) batteries, which hold great promise for grid energy storage systems. Achieving the reversible conversion reaction of high-valence iodine species, particularly I+/I0 redox chemistry, offers a substantial potential for improved energy density. In this study, we introduce a novel method of employing electron-outflowing heterostructured hosts to stabilize I+ ions in aqueous halide-free ZnSO4 electrolytes. Both experimental analyses and density functional theory (DFT) calculations reveal that the stabilization of thermodynamically unstable I+ cations originates from the charge transfer interaction between I+ ions and copper phthalocyanine (CuPc) within the hosts. The electron-outflowing effect resulting from the π-π conjugation between CuPc and the carbon framework in heterostructured hosts further intensifies the charge transfer interaction, leading to the reversible I+/I5− conversion reaction in Zn-I2 batteries. Consequently, this emerging redox reaction, validated by in-situ Raman and ex-situ ultraviolet-visible spectroscopy, introduces another voltage plateau at ∼1.6 V and enhances the energy density to 233.8 Wh kg–1 at 3.0 A g–1. This work showcases outstanding electrochemical performance for the Zn-I2 battery, providing valuable insights into advancing iodine redox chemistry featuring multiple electrons.

Highly Electrically Conductive Polyiodide Ionic Liquid Cathode for High-Capacity Dual-Plating Zinc-Iodine Batteries.

Zinc-iodine batteries are one of the most intriguing types of batteries that offer high energy density and low toxicity. However, the low intrinsic conductivity of iodine, together with high polyiodide solubility in aqueous electrolytes limits the development of high-areal-capacity zinc-iodine batteries with high stability, especially at low current densities. Herein, we proposed a hydrophobic polyiodide ionic liquid as a zinc-ion battery cathode, which successfully activates the iodine redox process by offering 4 orders of magnitude higher intrinsic electrical conductivity and remarkably lower solubility that suppressed the polyiodide shuttle in a dual-plating zinc-iodine cell. By the molecular engineering of the chemical structure of the polyiodide ionic liquid, the electronic conductivity can reach 3.4 × 10-3 S cm-1 with a high Coulombic efficiency of 98.2%. The areal capacity of the zinc-iodine battery can achieve 5.04 mAh cm-2 and stably operate at 3.12 mAh cm-2 for over 990 h. Besides, a laser-scribing designed flexible dual-plating-type microbattery based on a polyiodide ionic liquid cathode also exhibits stable cycling in both a single cell and 4 × 4 integrated cell, which can operate with the polarity-switching model with high stability.

A Bifunctional Electrolyte Additive Features Preferential Coordination with Iodine toward Ultralong‐Life Zinc–Iodine Batteries

AbstractAqueous zinc–iodine (Zn‐I2) battery is one of the most promising candidates for large‐scale energy storage due to its cost‐effectiveness, environmental friendliness, and recyclability. Its practical application is hindered by challenges including polyiodide “shuttle effect” in the cathode and anode corrosion. In this study, a zinc pyrrolidone carboxylate bifunctional additive is introduced to simultaneously tackle the issues of the polyiodide and Zn anode. It is revealed that the pyrrolidone carboxylate anions decrease the polyiodide concentration by preferential coordination between the pyrrolidone carboxylate anions and I2 based on the Lewis acid‐base effect, suppressing the shuttle effect and therefore improving the conversion kinetics for the iodine redox process. Meanwhile, the pyrrolidone carboxylate anions adsorbed on the Zn anode inhibit Zn corrosion and promote non‐dendritic Zn plating, contributing to impressive Coulombic efficiency and long‐term cycling stability. As a result, the Zn‐I2 full battery with the bifunctional zinc pyrrolidone carboxylate additive realizes a high specific capacity of 211 mAh g−1 (≈100% iodine utilization rate), and an ultralong cycling life of >30 000 cycles with 87% capacity retention. These findings highlight the significant potential of zinc pyrrolidone carboxylate as a transformative additive for aqueous Zn‐I2 batteries, marking a critical advancement in the field of energy storage technologies.

Secondary Amines Functionalized Organocatalytic Iodine Redox for High-Performance Aqueous Dual-Ion Batteries.

Aqueous dual-ion batteries (ADIBs) based on the cooperative redox of cations and iodine anions at the anode and cathode respectively, are attracting increasing interest because of high capacity and safety. However, the full-cell performance is limited by the sluggish iodine redox kinetics between iodide and polyiodide involving multiple electron transfer steps, and the undesirable shuttling effect of polyiodides. Here, this work reports a versatile conjugated microporous polymer functionalized with secondary amine groups as an organocatalytic cathode for ADIB, which can be positively charged and electrostatically adsorb iodide, and organocatalyze iodine redox reactions through the amine groups. Both theoretical calculations and controlled experiments confirm that the secondary amine groups confine (poly)iodide species via hydrogen bonding, which is essential for accelerating iodine redox kinetics and reducing the polyiodide shuttling effect. The ADIB achieves an ultrahigh capacity of 730 mAh g-1 with an ultrasmall overpotential of 47mV at 1 A g-1 , which also exhibits excellent rate performance and long cycling stability with a capacity retention of 74% after 5000 cycles at a high current density of 5 A g-1 . This work demonstrates the promise of developing organocatalysts for accelerating electrochemical processes, which remains a virtually unexplored area in electrocatalyst design for clean energy applications.

Suppression of Charge Recombination by Vertical Arrangement of A Donor Moiety on Flat Planar Dyes for Efficient Dye-Sensitized Solar Cells.

In dye-sensitized solar cells (DSSCs), flat planar dyes (e. g., highly light-harvesting porphyrins and corroles) with multiple anchoring groups are known to adopt a horizontal orientation on TiO2 through the multiple binding to TiO2. Due to the strong electronic coupling between the dye and TiO2, fast charge recombination between the oxidized dye and an electron in TiO2 occurs, lowering the power conversion efficiency (η). To overcome this situation, an additional donor moiety can be placed on top of the planar dye on TiO2 to slow down the undesirable charge recombination. Here we report the synthesis and photovoltaic properties of a triarylamine (TAA)-tethered gold(III) corrole (TAA-AuCor). The DSSC with TAA-AuCor using iodine redox shuttle exhibited the highest η-value among corrole-based DSSCs, which is much higher than that with the reference AuCor. The transient absorption spectroscopies clearly demonstrated that fast electron transfer from the TAA moiety to the corrole radical cation in TAA-AuCor competes with the undesirable charge recombination to generate long-lived charge separated state TAA⋅+-Cor/TiO2⋅- efficiently. Consequently, the introduction of the TAA moiety enhanced the η-value remarkably, demonstrating the usefulness of our new concept to manipulate charge-separated states toward highly efficient DSSCs.

Rates and pathways of iodine speciation transformations at the Bermuda Atlantic Time Series

The distribution of iodine in the surface ocean – of which iodide-iodine is a large destructor of tropospheric ozone (O3) – can be attributed to both in situ (i.e., biological) and ex situ (i.e., mixing) drivers. Currently, uncertainty regarding the rates and mechanisms of iodide (I-) oxidation render it difficult to distinguish the importance of in situ reactions vs ex situ mixing in driving iodine’s distribution, thus leading to uncertainty in climatological ozone atmospheric models. It has been hypothesized that reactive oxygen species (ROS), such as superoxide (O2•−) or hydrogen peroxide (H2O2), may be needed for I- oxidation to occur at the sea surface, but this has yet to be demonstrated in natural marine waters. To test the role of ROS in iodine redox transformations, shipboard isotope tracer incubations were conducted as part of the Bermuda Atlantic Time Series (BATS) in the Sargasso Sea in September of 2018. Incubation trials evaluated the effects of ROS (O2•−, H2O2) on iodine redox transformations over time and at euphotic and sub-photic depths. Rates of I- oxidation were assessed using a 129I- tracer (t1/2 ~15.7 Myr) added to all incubations, and 129I/127I ratios of individual iodine species (I-, IO3-). Our results show a lack of I- oxidation to IO3- within the resolution of our tracer approach – i.e., <2.99 nM/day, or <1091.4 nM/yr. In addition, we present new ROS data from BATS and compare our iodine speciation profiles to that from two previous studies conducted at BATS, which demonstrate long-term iodine stability. These results indicate that ex situ processes, such as vertical mixing, may play an important role in broader iodine species’ distribution in this and similar regions.

Activating iodine redox by enabling single-atom coordination to dormant nitrogen sites to realize durable zinc–iodine batteries

The introduction of a single Ni atom into an inactive N-doped carbon matrix, through its role as an electrocatalyst, awakens the dormant N sites, significantly suppressing the polyiodide shuttle effect and enhancing iodine redox kinetics.

Highly stable and high performance iodine redox flow batteries using host–guest interaction of (2-hydroxypropyl)-β-cyclodextrin additive

This study focuses on enhancing the stability of ARFBs using iodine as active material for the catholyte and (2-hydroxypropyl)-β-cyclodextrin as additive, to increase the solubility of I2 and activate the reaction of iodine to form the I3− ion.

Triflate anion chemistry for enhanced four-electron zinc-iodine aqueous batteries.

I+ hydrolysis, sluggish iodine redox kinetics and the instability of Zn anodes are the primary challenges for aqueous four-electron zinc-iodine batteries (4eZIBs). Herein, the OTf- anion chemistry in aqueous electrolyte is essential for developing advanced 4eZIBs. It is elucidated that OTf- anions establish weak hydrogen bonds (H bonds) with water to stabilize I+ species while optimizing a water-lean Zn2+ coordination structure to mitigate Zn dendrites and corrosion. Moreover, the interaction of the OTf- anions with the iodine species results in an increased equilibrium average intermolecular bond length of the iodine species, facilitating the 4e redox kinetics of iodine with improved reversibility.

Refining the carbonate-associated iodine redox proxy with leaching experiments

Iodate ions can substitute for carbonate in crystal lattices, which is why carbonate-associated iodine (CAI) is increasingly being used to track redox-sensitive iodine species, and by extrapolation, the redox conditions of ancient oceans. Extracting iodine from carbonate rocks is challenging, however, because iodine is susceptible to volatilization in acidic solutions. A broadly similar leaching scheme with different leaching times has been applied to all kinds of ancient carbonate rocks. However, the effects of non‑carbonate phases and iodine stability during leaching remain under-constrained, which limits its use for paleoredox reconstruction. For this study, we assessed these issues by conducting a series of leaching experiments on carbonate standards and ancient carbonate rocks of varying purity. We first developed an alternative stabilizer for iodine, i.e., 3% EDTA (ethylenediaminetetraacetic acid) in 3% NH4OH (ammonium hydroxide). This easily accessible new stabilizer effectively prevents the precipitation of metal ions from the alkaline solution, thus easing the preparation process and reducing the iodine signal drift during the CAI analysis. We also propose two interlaboratory limestone standards for iodine analysis with long-term (one year) I/Ca values of 0.43 ± 0.03 μmol/mol for limestone CRM-393 and 0.99 ± 0.06 μmol/mol for argillaceous limestone SRM-1c. Here we demonstrate that excessive leaching times (>60 min) can lead to the loss of nearly half of the iodine released under typical leaching conditions. Bulk carbonate digestion is shown to potentially underestimate primary CAI concentrations due to the presence of diagenetic carbonates. Moreover, we identified phosphates and organic matter as potential contaminants, the inadvertent leaching of which could lead to overestimated concentrations. Although the potential significance of such contamination warrants further study, our results show that contamination, if present, can be minimised by oxidative cleaning with 12% NaClO followed by dissolution in 0.3 M acetic acid. The possibility that measured CAI concentrations can be both under- and over-estimated may lead to reassessment of oxygenation events identified from the iodine concentrations of impure carbonate rocks.

Bidirectional Confined Redox Catalysis Manipulated Quasi-Solid Iodine Conversion for Shuttle-Free Solid-State Zn-I2 Battery.

Electrochemically reversible conversion of I2/I- redox couple in a controllable iodine speciation manner is the eternal target for practical metal-iodine batteries. This contribution demonstrates an advanced polyiodide-free Zn-I2 battery achieved by the bidirectional confined redox catalysis-directed quasi-solid iodine conversion. A core-shell structured iodine cathode is fabricated by integrating multiporous Prussian blue nanocubes as a catalytic mediator, and the polypyrrole sheath afforded a confinement environment that favored the iodine redox. The zincate Znx+1FeIII/II[Fe(CN)6]y has substantially faster zinc-ion intercalation kinetics and overlapping kinetic voltage profiles compared with the I2/ZnI2 redox, and behave as a redox mediator that catalyze reduction of polyiodides via chemical redox reactions during battery discharging and an exemplary reaction is Zn(I3)2+2Znx+1FeII[Fe(CN)6]y=3ZnI2+2ZnxFeIII[Fe(CN)6]y,ΔG=-19.3kJmol-1). During the following recharging process, the electrodeposited ZnI2 can be facially activated by iron redox hotspots, and the ZnxFe[FeIII/II(CN)6]y served as a cation-transfer mediator and spontaneously catalyze polyiodides oxidation (Zn(I3)2+2ZnxFe[FeIII(CN)6]y=3I2+2Znx+1Fe[FeII(CN)6]y,ΔG=-7.72kJmol-1), manipulating the reversible one-step conversion of ZnI2 back to I2. Accordingly, a flexible solid-state battery employing the designed cathode can deliver an energy density of 215Wh kgiodine -1.

Leveraging sulfonated poly(ether ether ketone) for superior performance in zinc iodine redox flow batteries

Sulfonated poly (ether ether ketone) SPEEK membranes with a degree of sulfonation of approximately 73 % were synthesized and investigated as the cation exchange membrane (CEM) for the zinc iodine (ZI) redox flow battery (RFB). Specifically, SPEEK was used in ZI RFB with 1 mol L−1 electrolyte and its performance was compared to the current benchmark CEM, Nafion™. Notably, columbic and energy efficiencies of 92.9 % and 75.9 %, respectively, were measured for the ZI battery with SPEEK at 17 mA cm−2, which was a 370 % increase in energy density compared to those with Nafion 212 membranes. RFBs with SPEEK exbibit a peak power density of 122 mW cm−2 at a current density of 166 mA cm−2 (98 mW/cm2 at 133 mA/cm2 with Nafion 212) because of their lower overpotential and higher discharge voltage. These results demonstrate the high cation selectivity of the SPEEK membranes in neutral, salt-based electrolytes, and provide the groundwork to develop a suitable replacement to Nafion for low-cost RFBs.