Multielectron Storage Research Articles

Redox Self-Equilibration in Molecular Vanadium Oxide Mixtures Enables Multi-Electron Storage.

Polyoxometalates (POMs) are ideal components for reversible multi-electron storage in energy technologies. To-date, most redox-applications employ only single, individual POM species, which limits the number of electrons that can be stored within a given potential window. Here, we report that spontaneous redox self-equilibration during cluster synthesis leads to the formation of two structurally related polyoxovanadates which subsequently aggregate into co-crystals. This results in systems with significantly increased redox reactivity. The mixed POM system was formed by non-aqueous self-assembly of a vanadate precursor in the presence of Mg2+, resulting in two mixed-valent (VIV/V) species, [(MgOH)V13O33Cl]4- (={MgV13}) and the di-vanadium-functionalized species [V14O34Cl]4- (={V14}), which co-crystallize in a 1 : 1 molar stoichiometry. Experimental data indicate that in the native state, {MgV13} is reduced by three electrons, and {V14} is reduced by five electrons. Electrochemical studies in solution show, that the system can reversibly undergo up to fourteen redox transitions (tentatively assigned to twelve 1-electron processes and two 2-electron processes) in the potential range between -2.15 V to +1.35 V (vs Fc+/Fc). The study demonstrates how highly redox-active, well-defined molecular mixtures of mixed-valent molecular metal oxides can be accessed by redox-equilibration during synthesis, opening new avenues for molecular energy storage.

Dithiolate-Based Scorpion Arm Ligand Synthesis and Characterization

Redox flow batteries (RFBs) play a vital role in the efficient and reliable utilization of renewable energy sources by providing a means to capture and store excess energy for later use.1–6 The synthesis and characterization of a novel scorpionate arm ligand, i-mntPy- (2,2-dicyano-1-pyridin-2-ylmethyl-1,1-dithiolate), are presented in this study. The ligand i-mntPy- was synthesized through a multistep synthetic route, starting from commercially available precursors. The chemical structure of the ligand was confirmed using various spectroscopic techniques, including NMR spectroscopy, ESI-MS, and Elemental analysis. Furthermore, the coordination ability of i-mntPy- to facilitate 2e- transfer in M(II/IV) coordination environment was investigated by the computational study and addition of Ni(II) and Pd(II) ions in the i-mntPy- solution. The results demonstrate the successful synthesis and characterization of the novel scorpionate arm ligand i-mntPy-, which coordinates with d8 metal centers and holds promise for future applications in coordination chemistry and energy storage. References (1) Mazumder, Md. M. R.; Jadhav, R. G.; Minteer, S. D. Phenyl Acrylate-Based Cross-Linked Anion Exchange Membranes for Non-Aqueous Redox Flow Batteries. ACS Mater. Au 2023. https://doi.org/10.1021/acsmaterialsau.3c00044.(2) Rahaman Mazumder, M. M.; Islam, R.; Khan, M. A. R.; Anis‐Ul‐Haque, K. M.; Rahman, M. M. Efficient AcFc‐[Fe III (Acac) 3 ] Redox Couple for Non‐aqueous Redox Flow Battery at Low Temperature. Chem. – Asian J. 2023, 18 (1). https://doi.org/10.1002/asia.202201025.(3) Mazumder, Md. M. R.; Dalpati, N.; Pokkuluri, P. R.; Farnum, B. H. Zinc-Catalyzed Two-Electron Nickel(IV/II) Redox Couple for Multi-Electron Storage in Redox Flow Batteries. Inorg. Chem. 2022, 61 (48), 19039–19048. https://doi.org/10.1021/acs.inorgchem.2c03124.(4) Mazumder, Md. M. R.; Burton, A.; Richburg, C. S.; Saha, S.; Cronin, B.; Duin, E.; Farnum, B. H. Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate. Inorg. Chem. 2021, acs.inorgchem.1c01699. https://doi.org/10.1021/acs.inorgchem.1c01699.(5) MAZUMDER MDMOTIURRAHAMAN, Islam R. Temperature-dependent study of AcFc-FeIII(acac)3 redox couple for non-aqueous redox flow battery. ChemRxiv. Cambridge: Cambridge Open Engage; 2022; https://doi.org/10.26434/chemrxiv-2022-3177p(6) Islam, R.; Mazumder, M. M. R.; Farnum, B. H. Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage. ECS Meet. Abstr. 2021, MA2021-01 (1), 54–54. https://doi.org/10.1149/ma2021-01154mtgabs. Figure 1

Cross-Linked Anion Exchange Membranes for Non-Aqueous Redox Flow Battery

The development of redox flow batteries (RFBs) has been one of the primary responses to the need to store harvested renewable energy for improving grid reliability and utilization.1–6 In this study, we synthesized and characterized different Bromobutyl Norbornene backbone-based anion-exchange membranes (AEM) with different Tetramethyl hexadiamine crosslinker amounts and explored the performance of AEMs in non-aqueous redox flow batteries under ideal conditions. Performance was compared based on high stability in a non-aqueous solvent, high permeability to the charge-carrying ion, low electric cell resistance, low cross-over of the redox-active molecules, high mechanical property, and low cost. 100 cycles battery data indicates that Bromobutyl Norbornene-based AEM performance is far better than the commercial best membrane Fuma-375. The best membrane will be found which will show no cross-over of redox-active electrolytes after 1000 battery cycle experiments and exhibit low resistance and high structural/chemical stability in MeCN solvent. References (1) Mazumder, Md. M. R.; Burton, A.; Richburg, C. S.; Saha, S.; Cronin, B.; Duin, E.; Farnum, B. H. Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate. Inorg. Chem. 2021, 60 (17), 13388–13399. https://doi.org/10.1021/acs.inorgchem.1c01699.(2) Mazumder, M. M. R.; Farnum, B. H. Two One Electron vs One Two-Electron Redox System of Nickel Diethyldithiocarbamate for Redox Flow Battery; ACS, 2021. https://doi.org/10.1021/scimeetings.1c00951.(3) Mazumder, M. M. R. Ni(IV/II) Redox Couple 2e- Reversibility Improvement for Redox Flow Battery. ECS Meet. Abstr. 2021, MA2021-02 (5), 1855–1855. https://doi.org/10.1149/ma2021-0251855mtgabs.(4) Islam, R.; Mazumder, M. M. R.; Farnum, B. H. Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage. ECS Meet. Abstr. 2021, MA2021-01 (1), 54–54. https://doi.org/10.1149/ma2021-01154mtgabs.(5) Rahaman Mazumder, M. M.; Islam, R.; Khan, M. A. R.; Anis‐Ul‐Haque, K. M.; Rahman, M. M. Efficient AcFc‐[Fe III (Acac) 3 ] Redox Couple for Non‐aqueous Redox Flow Battery at Low Temperature. Chem. – Asian J. 2023, 18 (1). https://doi.org/10.1002/asia.202201025.(6) Mazumder, Md. M. R.; Dalpati, N.; Pokkuluri, P. R.; Farnum, B. H. Zinc-Catalyzed Two-Electron Nickel(IV/II) Redox Couple for Multi-Electron Storage in Redox Flow Batteries. Inorg. Chem. 2022, 61 (48), 19039–19048. https://doi.org/10.1021/acs.inorgchem.2c03124.

Defect regulation in bimetallic oxide cathodes for significantly improving the performance of flexible aqueous Zn-ion batteries

Bimetallic oxides have received extensive attention as cathode materials in aqueous zinc-ion batteries (AZIBs) due to their effective multi-electron storage mechanism. However, their capacity still falls short of the current demand. In this study, through reasonable structural design, we synthesized spherical glucose-derived carbon-regulated defect state Zn3V3O8 (ZVO) bimetallic oxide (CS@ZVO) cathode. Such a design avoids the layered accumulation of electrode materials, which prevents the structural collapse during the cycle process, leading to a significant improvement in the cycle stability of AZIBs. Additionally, the introduction of glucose-derived carbon can shift the valence state of vanadium in the ZVO bimetallic oxide cathode towards reduction, thereby significantly improving its Zn-ion storage capacity. The resulting CS@ZVO cathode manifests a high discharge capacity of 154 mAh g−1 at 1 A g−1 after 100 cycles and a stable lifespan of 2000 cycles at 5 A g−1. We also constructed a flexible and foldable AZIB using a hydrogel electrolyte, which operates with a specific capacity of up to 230 mAh g−1 at 0.5 A g−1 and can be bent and folded arbitrarily when working. This strategy for regulating the valence state of bimetallic oxides offers a promising path for the development of cathode materials in flexible AZIBs.

Zinc-Catalyzed Two-Electron Nickel(IV/II) Redox Couple for Multi-Electron Storage in Redox Flow Batteries.

Energy storage is a vital aspect for the successful implementation of renewable energy resources on a global scale. Herein, we investigated the redox cycle of nickel(II) bis(diethyldithiocarbamate), NiII(dtc)2, for potential use as a multielectron storage catholyte in nonaqueous redox flow batteries (RFBs). Previous studies have shown that the unique redox cycle of NiII(dtc)2 offers 2e- chemistry upon oxidation from NiII → NiIV but 1e- chemistry upon reduction from NiIV → NiIII → NiII. Electrochemical experiments presented here show that the addition of as little as 10 mol % ZnII(ClO4)2 to the electrolyte consolidates the two 1e- reduction peaks into a single 2e- reduction where [NiIV(dtc)3]+ is reduced directly to NiII(dtc)2. This catalytic enhancement is believed to be due to ZnII removal of a dtc- ligand from a NiIII(dtc)3 intermediate, resulting in more facile reduction to NiII(dtc)2. The addition of ZnII also improves the 2e- oxidation, shifting the anodic peak negative and decreasing the 2e- peak separation. H-cell cycling experiments showed that 97% Coulombic efficiency and 98% charge storage efficiency was maintained for 50 cycles over 25 h using 0.1 M ZnII(ClO4)2 as the supporting electrolyte. If ZnII(ClO4)2 was replaced with TBAPF6 in the electrolyte, the Coulombic efficiency fell to 78%. The use of ZnII to increase the reversibility of 2e- transfer is a promising result that points to the ability to use nickel dithiocarbonates for multielectron storage in RFBs.

High-Voltage Symmetric Nonaqueous Redox Flow Battery Based on Modularly Tunable [Ru2M(μ3-O)(CH3CO2)6(py)3] (M = Ru, Mn, Co, Ni, Zn) Cluster Compounds with Multielectron Storage Capability

Redox flow batteries (RFBs) provide an attractive solution for large-scale energy buffering and storage. This report describes the development of nonaqueous RFBs based on trimetallic coordination cluster compounds: [Ru2M(μ3-O)(CH3CO2)6(py)3] (M = Ru, Mn, Co, Ni, Zn). The all-ruthenium complex exhibited stable battery cycles in anolyte–catholyte symmetric operation, with rarely observed multielectron storage in a single molecule. Moreover, the complex holds modularly tunable synthetic handles for systematic improvements in solubility and redox potentials. An optimized battery stack containing [Ru3(μ3-O)(CH3CO2)6(py)3]+ anolyte and [Ru2Co(μ3-O)(CH3CO2)6(py)3] catholyte yielded stable cycles with a discharge voltage of 2.4 V, comparable to the state-of-the-art nonaqueous RFBs. Explanation for the exceptional stability of the charged states and prediction of systematic tunability of the redox potentials of the cluster compounds were assisted by DFT calculations.

Reversible Multi-Electron Storage Enabled by Na5V(PO4)2F2 for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMB) are one of the utmost promising post-lithium energy storage technologies due to their high theoretical energy density, affordable low cost, and inherent safety with moisture and air. Nonetheless, the research of RMB has been limited due to the low power and reversible energy densities of available cathode materials. Herein, we report a new Mg battery cathode of trigonal Na5V(PO4)2F2 (t­-NVPF) which performs 136 mA h g−1 reversible capacity realizing multi-electron storage through the V4+/V3+ and V5+/V4+ redox couples. After the first reversible cycle MgNa3V(PO4)2F2 is formed. The geometry optimization and energy calculations on the systems MgxNa3V(PO4)2F2 were carried within the density functional theory (DFT) demonstrating Mg insertion can fill the Na6, Na8, and Na9 sites, and evidenced a 1.5 V difference for the same redox couple comparing with the experimental results. Some facets of its crystal and local structure are determined by XRD, EPR, XPS, and 31P and 51V solid-state NMR spectroscopy. The cells cycled 2.5 – 0.2 V vs. Mg2+/Mg and at low current densities exhibited diminished polarization. The average cell potential is 1.4 V, entailing an energy density of 190 W h kg-1­ at the materials’ level. This piece of work provides an effective strategy for designing multi-electron storage for high-energy rechargeable Mg batteries, but more efforts are required to overcome high polarization during charge-discharge cycles which are commonly found in Mg batteries.

Fast and Reversible Four-Electron Storage Enabled By Ethyl Viologen for Rechargeable Magnesium Batteries

Magnesium (Mg) batteries have been considered one of the most promising “post-lithium-ion” energy storage technologies owing to their high theoretical energy density, earth abundance, and intrinsic safety with air and moisture. However, the cell performance of Mg batteries has been limited to cathode materials leading to sluggish kinetics, low reversible energy density, and poor cycling stability. The development of Mg intercalation cathode materials[1–3] has been impeded by slow Mg2+ solid diffusion due to high charge density, sluggish charge redistribution, and strong electrostatic interaction with host and anions.[4] Many of the Li+-intercalation cathodes are not suitable for Mg2+ insertion.[5] Organic materials with high tunability have attracted significant attention,[6] but it has been challenging to achieve organic Mg batteries with a satisfactory energy density as the commercial lithium-ion battery (100-170 Wh kg-1 [7]) with high power and long cycle life. Here, a new organic cathode for rechargeable Mg batteries is reported based on ethyl viologen (EV), which not only has a fast redox couple EV2+/EV0 but also is capable of coupling with redox-active anions, such as iodide (I-), achieving a total four-electron storage. The EV2+/EV0 redox couple demonstrates a stable cycle life (500 cycles) with a superior rate performance (10 C) owing to intrinsic fast electrode kinetics, and a high material utilization (>80%) was achieved at 1.0 C under a high areal loading of 5 mg cm−2. When coupling with iodide I-, a reversible four-electron storage is achieved with a high energy density (304.2 Wh kg-1) and a stable cycle life (>100 cycles). This study provides effective strategies for designing reversible multielectron storage for high-rate and high-energy rechargeable Mg batteries.[8] Reference s : [1] X. Sun, P. Bonnick, V. Duffort, M. Liu, Z. Rong, K. A. Persson, G. Ceder, L. F. Nazar, Energy Environ. Sci. 9 (2016) 2273-2277.[2] X. Sun, P. Bonnick, L. F. Nazar, ACS Energy Lett. 1 (2016) 297-301.[3] B. Liu, T. Luo, G. Mu, X. Wang, D. Chen, G. Shen, ACS nano 7 (2013) 8051-8058.[4] E. Levi, M. D. Levi, O. Chasid, D. Aurbach, J Electroceram. 22 (2009) 13-19.[5] M. Bouroushian, Electrochemistry of metal chalcogenides, Springer Science & Business Media, Heidelberg, Berlin, 2010.[6] M. Mao, T. Gao, S. Hou, C. Wang, Chem. Soc. Rev. 47 (2018) 8804-8841.[7] J.-M. Tarascon, M. Armand, in: V. Dusastre (Ed.), Materials for Sustainable Energy: A Collection of Peer-Reviewed Research and Review Articles from Nature Publishing Group, World Scientific, Singapore, 2011, pp. 171–179.[8] Y. Sun, Q. Zou, Y. Lu, Adv. Energy Mater. 9 (2019) 1903002. Acknowledgements : This work was supported by a grant from the Research Grants Council (RGC) of the Hong Kong Administrative Region, China, under an RGC project No. T23-601/17-R.

Photoinduced Charge Accumulation and Prolonged Multielectron Storage for the Separation of Light and Dark Reaction.

The utilization of solar energy is restricted by the intermittent nature of solar influx. We present novel noble-metal free complexes that can be photochemically charged in the presence of sacrificial electron donors and remain stable in its charged form for over 14 h. This allows the doubly reduced Cu(I) 4H-imidazolate complex to be stored after photochemical charging and used as a reagent in dark reactions, such as the reduction of methyl viologen or oxygen. Combined UV-vis/EPR spectroelectrochemistry indicates that a two-electron reduction is induced by introducing sacrificial electron donors that facilitate proton-coupled electron transfer. Repeated photochemical reduction and chemical oxidation reveals that the complex retained a charging capacity of 72% after four cycles. We demonstrate a chemical system that can decouple photochemical processes from the day-night cycle, which has been a barrier to realizing utilization of solar energy in photochemical processes on a global scale.

Fast and Reversible Four‐Electron Storage Enabled by Ethyl Viologen for Rechargeable Magnesium Batteries

AbstractMagnesium (Mg) batteries are the most promising “post‐lithium‐ion” energy storage technologies owing to their high theoretical energy density, low cost, and intrinsic safety with air and moisture. However, the development of Mg batteries has been limited to cathode materials leading to low power, low reversible energy density, and poor cycle life. Here, a new Mg cathode is reported based on ethyl viologen (EV), which not only has a fast redox couple EV2+/EV0 but also is capable of coupling with redox‐active anions, such as iodide (I−), achieving a total four‐electron storage. The EV2+/EV0 redox couple demonstrates a superior rate performance (10 C) and stable cycle life (500 cycles) owing to intrinsic fast electrode kinetics. A high material utilization (>80%) can be achieved at 1.0 C under a high areal loading of 5 mg cm−2. When coupling with iodide I−, a reversible four‐electron storage is achieved with a high energy density (304.2 Wh kg−1) and a stable cycle life (>100 cycles). This study provides effective strategies for designing reversible multielectron storage for high‐rate and high‐energy rechargeable Mg batteries.

Photocatalytic H2 Evolution Using a Ru Chromophore Tethered to Six Viologen Acceptors.

A new photo-charge separator (PCS) consisting of a [Ru(bpy)3 ]2+ (bpy=2,2'-bipyridine) chromophore and six viologen (MV2+ ) acceptors, [Ru(bpyMV2)3 ]14+ , is synthesized and its application in the photocatalytic H2 evolution reaction is reported. The present PCS possesses shorter linkers for connecting the Ru chromophore and the MV2+ acceptors in comparison with our previous PCSs (Inorg. Chem. Front., 2016, 3, 671-680) and shows a consecutive photo-driven electron transfer in the presence of a sacrificial electron donor [ethylenediaminetetraacetic acid (EDTA)], leading to a multi-electron storage over the PCS. This behavior can also be coupled with the catalytic H2 evolution by the presence of a colloidal Pt catalyst. More importantly, the present PCS exhibits a much higher durability during the photolysis, which is attributed to the higher rate in the catalytic process. The high durability is also attributed to its bulky framework preventing undesirable side reactions.

Exceptionally Long-Lived Photodriven Multi-Electron Storage without Sacrificial Reagents.

Photoexcitation of a molecular pentad in the presence of Sc3+ in de-aerated CH3 CN leads to a quinone dianion that is stable on the millisecond timescale. Light-driven electron accumulation on the quinone unit is sensitized by two Ru(bpy)32+ complexes in an intramolecular process, which relies on covalently attached triarylamine donors rather than on sacrificial reagents. Lewis acid-Lewis base interactions between Sc3+ and quinone dianion are responsible for the exceptionally long lifetime of this photoproduct. Our study of photoinduced multi-electron transfer is relevant in the greater context of solar energy conversion.

Structural deformation of a ring-shaped Re(I) diimine dinuclear complex in the excited state

We investigated the excited state of a ring-shaped dinuclear Re(I) diimine bis-carbonyl complex that shows promise with regard to efficient photosensitized reactions and multi-electron storage, using time-resolved infrared (TR-IR) vibrational spectroscopy and quantum chemical calculations. Anomalous peaks in the CO stretching region of the TR-IR spectrum were well reproduced by the calculations. It was found that metal-to-ligand charge transfer occurs only in one of the Re complex units, and that the excited state geometry is deformed relative to the ground state in order to relax the associated steric tension. This structural deformation generates the unique photophysical properties of the complex.

Resonance Raman studies of photochemical molecular devices for multielectron storage

AbstractResonance Raman spectroscopy was utilized for the first time to characterize the nature of the 1metal‐to‐ligand charge transfer (MLCT) state of a ruthenium complex containing the redoxactive tetraazatetrapyrido‐pentacene (tatpp) ligand. The presented results show that the long‐wavelength absorption is originating from transitions involving the terminal phenanthroline and the tatpp ligands. Copyright © 2008 John Wiley & Sons, Ltd.

Multi-electron storage of photoenergy using Cu 2O–TiO 2 thin film photocatalyst

UV–vis irradiation of thin films of TiO 2 (ITO/TiO 2) and Cu 2O/TiO 2 (ITO/Cu 2O/TiO 2) coated on conducting glasses generate H 2 from H 2O and once the illumination is ceased, the H 2 production was still noticeable under dark for ITO/Cu 2O/TiO 2 at a lesser production rate for up to 2 h. No such dark reactions were observed for ITO/TiO 2 or TiO 2-coated copper metal foil (Cu/TiO 2). It was noticed that the irradiation of ITO/Cu 2O/TiO 2 leads to formation of trapped electrons and this stored energy leads to generate H 2 from H 2O in the dark.

Primary charge separation in photoinduced multielectron storage systems. A dinuclear ruthenium(ii) species featuring a charge-separated state with a lifetime of 1.3 µs

The primary photoinduced charge separation and recombination processes occurring in a dinuclear Ru(II) complex capable to perform multielectron storage upon light excitation have been studied in different solvents: the charge-separated state obtained in dichloromethane is, to the best of our knowledge, the longest-lived ever reported for a ruthenium polypyridine complex.

Multielectron storage and hydrogen generation with colloidal semiconductors

Multielectron storage and hydrogen generation by light is achieved in aqueous dispersions of ultrafine TiO(2) particles (120-A diameter) when the amphiphilic viologen derivative N-tetradecyl-N'-methyl-4,4'-dipyridinium dichloride (C(14)MV(2+)) is used as an electron relay. Consecutive reduction of C(14)MV(2+) to the radical ion (C(14)MV(+)) and neutral (C(14)MV(0)) was observed after band-gap excitation of the semiconductor particle. Through surface adsorption of the relay, these electron-transfer reactions can occur very rapidly and are completed within less than 100 musec (pH 11). Two-electron reduction of C(14)MV(2+) can be coupled with H(2) generation in alkaline medium in the presence of Pt catalyst codeposited onto the TiO(2) particle. Electron-relay-free systems are 1/15th as efficient in producing H(2) at the same pH.