Redox-active Moieties Research Articles

(Keynote) Molecular Engineering Strategies for Symmetric Aqueous Organic Redox Flow Batteries

In this contribution we use electronic structure calculations to reveal structure-property relationships for symmetric aqueous organic redox flow battery (RFB) materials. Unlike normal asymmetric RFBs, the symmetric ones are based on bipolar electrolytes that exist in at least three oxidation states and can undergo a minimum of two distinct redox processes. We compute from first principles the redox potentials of selected electrolytes based on quinone, pyrazine, and pyridazine redox-active moieties.[1] The objective is to understand how the interaction between the redox units affects the potentials and solvation energies. We find that electronic interaction between redox units and intramolecular hydrogen bonding can be exploited to tune the difference between the redox potentials, i.e., the theoretical voltage of the battery. The redox potentials can be further fine-tuned in either direction by adding substituents. Starting from these observations, we formulate a set of rules that will help in finding improved electrolytes for symmetric RFBs.[1] R. P. Fornari, M. Mesta, J. Hjelm, T. Vegge, P. de Silva, “Molecular Engineering Strategies for Symmetric Aqueous Organic Redox Flow Batteries”, ACS Materials Lett. 2020, 2, 3, 239–246.

Synthesis and characterization of viologen functionalized fluorene-containing poly(arylene ether ketone)s for polymer batteries

Organic polymers containing redox-active moieties have attracted increasing attention as electrode materials for high-performance rechargeable batteries due to their sustainability, flexibility, environmentally benign, and high stability. Herein, viologen functionalized fluorene-containing poly(arylene ether ketone)s (MV-FPAEKs) were synthesized by polycondensation, bromination, and quaternization in sequence. 1H NMR was used to monitor the degree of functionalization (DF), which increased with the increasing of the molar ratio of the bromination agent. The MV-FPAEK-96 with a DF of 96% for viologen was used as the active material for polymer cathode. The theoretical specific capacity was calculated to be 87.6 mAh g−1 based on the dual electron transfer per viologen unit. It had been found that the MV-FPAEK-96 battery delivered a discharge specific capacity of 87.1 mAh g−1 at a current rate of 0.1 C, and maintained 32.1 mAh g−1 after 100 galvanostatic cycles. In contrast, the small molecule of dimethyl viologen was highly soluble in the electrolyte, and the corresponding capacity decreased to negligible values after only 20 cycles. Therefore, the attachment of viologen to polymeric backbones is an effective strategy to increase the stability in electrolyte while maintaining the rechargeability, and the MV-FPAEK-96 is a promising redox-active candidate for polymer batteries.

Influence of Polymorphism on the Electrochemical Behavior of Dilithium (2,3-Dilithium-oxy)-terephthalate vs. Li

Organic electrode materials offer obvious opportunities to promote cost-effective and environmentally friendly rechargeable batteries. Over the last decade, tremendous progress has been made thanks to the use of molecular engineering focused on the tailoring of redox-active organic moieties. However, the electrochemical performance of organic host structures relies also on the crystal packing, like the inorganic counterparts, which calls for further efforts in terms of crystal chemistry to make a robust redox-active organic center electrochemically efficient in the solid state. Following our ongoing research aiming at elaborating lithiated organic cathode materials, we report herein on the impact of polymorphism on the electrochemical behavior of dilithium (2,3-dilithium-oxy-)terephthalate vs. Li. Having isolated dilithium (3-hydroxy-2-lithium-oxy)terephthalate through an incomplete acid-base neutralization reaction, its subsequent thermally induced decarboxylation mechanism led to the formation of a new polymorph of dilithium (2,3-dilithium-oxy-)terephthalate referred to as Li4-o-DHT (β-phase). This new phase is able to operate at 3.1 V vs. Li+/Li, which corresponds to a positive potential shift of +250 mV compared to the other polymorph formerly reported. Nevertheless, the overall electrochemical process characterized by a sluggish biphasic transition is impeded by a large polarization value limiting the recovered capacity upon cycling.

A Nonaqueous Redox-Matched Flow Battery with Charge Storage in Insoluble Polymer Beads.

We describe the nonaqueous redox‐matched flow battery (RMFB), where charge is stored on redox‐active moieties covalently tethered to non‐circulating, insoluble polymer beads and charge is transferred between the electrodes and the beads via soluble mediators with redox potentials matched to the active moieties on the beads. The RMFB reported herein uses ferrocene and viologen derivatives bound to crosslinked polystyrene beads. Charge storage in the beads leads to a high (approximately 1.0–1.7 M) effective concentration of active material in the reservoirs while preventing crossover of that material. The relatively low concentration of soluble mediators (15 mM) eliminates the need for high‐solubility molecules to create high energy density batteries. Nernstian redox exchange between the beads and redox‐matched mediators was fast relative to the cycle time of the RMFB. This approach is generalizable to many different redox‐active moieties via attachment to the versatile Merrifield resin.

Effective Design Strategy of Small Bipolar Molecules through Fused Conjugation toward 2.5 V Based Redox Flow Batteries.

Using bipolar redox-active molecules (BRMs) as active materials is a practical way to address electrolyte crossover and resultant unpredictable side reactions in redox-flow batteries. However, the development of BRMs is greatly hindered by difficulties in finding new molecules from limited redox-active moieties and in achieving high cell voltage to compete with existing flow battery chemistries. This study proposes a strategy for design of high-voltage BRMs using fused conjugation that regulates the redox potential of integrated redox-active moieties. As a demonstration, quaternary N and ketone redox moieties are used to construct a new BRM that shows a prominent voltage gap with good electrochemical stability. A symmetrical redox-flow cell based on this molecule exhibits a high voltage of 2.5 V and decent cycling stability. This study provides a general strategy for designing new BRMs that may enrich the cell chemistries of organic redox-flow batteries.

One polymer with three charge states for two types of lithium-ion batteries with different characteristics as needed

Organic batteries materials exhibit merits of diverse structures, high capacities, less pollution and abundant sources, therefore, developing high-performance organic electrode materials is promising for the next generation of rechargeable batteries. Various advanced organic cathode materials have been reported but most of them possess only two charge states and can be used for one kind of battery. Thus, it is challenging to design organic material with three charge states for two types of high-performance organic batteries with different characteristics as needed. Herein, we designed and synthesized a polymer named P-BQPZ, which integrates maximum n-type and p-type redox-active moieties into one stable polymer with minimum redox-inactive moieties, and thus it can be used for two types of long-life lithium-ion batteries with different features (e.g. high capacity or output potential) by using different redox-active sites. The cathode half-cell based on n-type redox-active reaction exhibits a high capacity of 431.3 mA h g−1 (2.4 V vs Li/Li+) at 50 mA g−1 and a high retention of 99.95% per cycle up to 500 cycles at 1,000 mA g−1. Furthermore, the cathode half-cell based on p-type redox-active reaction displays relatively high output voltage of 3.1 V (vs Li/Li+, 176.6 mA h g−1 at 50 mA g−1) and superior retention of 99.97% per cycle at 500 mA g−1 for 1,000 cycles. More importantly, two kinds of all-organic batteries by using P-BQPZ cathode also operate well.

Redox-Hopping-Based Charge Transport Mediated by Ru(II)-Polypyridyl Species Immobilized in a Mesoporous Metal-Organic Framework

Electronic charge transport through crystalline metal-organic frameworks (MOFs) can be accomplished by site-to-site electron (or hole) hopping, provided that redox-active sites, such as easily reducible or oxidizable MOF linkers, are present. If the framework itself is redox-inert, solvent-assisted ligand incorporation of redox-active moieties can serve to enable hopping-based charge transport. Here we have studied the redox hopping process within Ru-bpy@NU-1008, where Ru-bpy is a carboxylate-functionalized derivative, i.e., a node-ligating derivative, of the well-known chromophore Ru(2,2′-bipyridine)32+, and NU-1008 is a redox-inert MOF featuring hierarchical porosity and csq topology. Chronoamperometry experiments with electrode-supported thin films of Ru-bpy@NU-1008 show that charge transport is feasible through portions of the MOF, with other portions being inaccessible. Possible confounding features are the undersized c-pores that cross-connect 1D mesoporous channels, as ingress and egress of charge-compensating anions is believed to accompany the net oxidation of Ru(II) to Ru(III) and the reduction of Ru(III) to Ru(II). Phenomenologically, transport through the electroactive portion of the films is diffusion-like, with the magnitude of the apparent diffusion coefficient being 6 × 10−12 cm2/s.

2D Conjugated Covalent Organic Frameworks: Defined Synthesis and Tailor-Made Functions

ConspectusCovalent organic frameworks (COFs) are an emerging class of crystalline porous polymers and have received tremendous attention and research interest. COFs can be classified into two-dimensional (2D) and three-dimensional (3D) analogues. Resembling the architectures of porous graphene, 2D conjugated COFs have exhibited promising prospects in many fields, such as gas storage and separation, heterogeneous catalysis, sensing, photocatalysis, environmental remediation, drug delivery, energy storage and conversion, and so forth. However, efficient structural design for high-throughput production of crystalline 2D COFs remains challenging.In this Account, we summarize our recent contributions to the design, synthesis, and application exploration of 2D conjugated COFs. First, we raised an efficient "two-in-one" strategy for the facile synthesis of 2D imine COFs with good reproducibility and solvent adaptability. Thanks to this elaborate molecular design strategy, we could easily modulate the topology of COFs and fabricate COF films. In addition, we developed two approaches to stabilize the 2D conjugated COFs by using planar building blocks and donor-acceptor structures. We also proposed a skeleton engineering strategy to design COFs as electrode materials, through which redox-active orthoquinone moieties were stepwise-incorporated in the skeletons of isostructural 2D imine-linked COFs. This strategy enabled systematic investigations on a series of 2D conjugated COFs with analogous structures but different numbers of active sites for energy storage, which provides a good platform to unveil the underlying structure-property relationships. In addition, we recently developed a new kind of arylamine-linked 2D conjugated COFs. The electroactive diphenylamine linkages endowed these 2D conjugated COFs with extended conjugation and improved stability, which also conferred these COFs with excellent pseudocapacitive energy storage performance. Moreover, tailor-made sulfur-rich COFs were introduced that were synthesized by selective introduction of polysulfide or sulfonyl groups on the COF skeletons and were used for Li storage and proton conduction. At the end, the key challenges of 2D conjugated COFs toward practical applications and their future prospects are suggested. We hope that this Account will evoke new inspirations and innovative work in the field of 2D conjugated COFs in the near future, especially in some burgeoning and interdisciplinary research areas.

Stoichiometric carbocatalysis via epoxide-like C−S−O configuration on sulfur-doped biochar for environmental remediation

Heteroatom doping is a promising technique to enhance biochar for effective environmental remediation. However, development of electroactive heteroatom-doped biochars, e.g., sulfur-doped biochar, has been hindered due to complex nature of non-stoichiometric biomass-derived carbon and changeable electrochemical state of dopants. Herein, we produced a series of wood waste-derived biochars with customized levels of minerals and redox-active moieties, aiming to unravel the crucial factors for sulfur doping. Calcium (Ca) in biochar was found to preferentially coordinate with sulfur to form inactive inorganic sulfur minerals (i.e., CaSO4 and CaS) with inferior catalytic reactivity. After diminishing the inherent Ca minerals beforehand, we could introduce surface phenoxyl-type radicals (C−O•) and vacancy defects on the biochar to develop an electrophilic C−S−O bonding configuration, which guaranteed a high affinity towards peroxymonosulfate (PMS, 2.08 mM g−1, 30 min) and efficient removal of bisphenol A (BPA, 91.1%, 30 min). Scavenging experiments and in-situ Raman analyses indicated that the epoxide-like C−S−O structure induced nucleophilic addition of PMS to generate surface-bound singlet oxygen (1O2, major) and hydroxyl radicals (•OH, minor) through a preservative and stoichiometric interfacial reaction. Overall, the proposed approach overcomes the major hurdles in science-informed fabrication of sulfur-doped biochar and advances its development for environmental remediation.

High performance Li-, Na-, and K-ion storage in electrically conducting coordination polymers.

Coordination polymers (CPs) made of redox-active organic moieties and metal ions emerge as an important class of electroactive materials for battery applications. However, the design and synthesis of high voltage alkali-cation reservoir anionic CPs remains challenging, hindering their practical applications. Herein, we report a family of electrically conducting alkali-cation reservoir CPs with the general formula of A2-TM-PTtSA (wherein A = Li+, Na+, or K+; TM = Fe2+, Co2+, or Mn2+; and PTtSA = benzene-1,2,4,5-tetra-methylsulfonamide). The incorporation of transition metal centers not only enables intrinsic high electrical conductivity, but also shows an impressive redox potential increase of as high as 1 V as compared to A4-PTtSA analogues, resulting in a class of organometallic cathode materials with a high average redox potential of 2.95–3.25 V for Li-, Na- and K-ion batteries. A detailed structure – composition – physicochemical properties – performance correlation study is provided relying on experimental and computational analysis. The best performing candidate shows excellent rate capability (86% of the nominal capacity retained at 10C rate), remarkable cycling stability (96.5% after 1000 cycles), outstanding tolerance to low carbon content (5 wt%), high mass loading (50 mg cm−2), and extreme utilisation conditions of low earth orbit space environment tests. The significance of the disclosed alkali-ion reservoir cathodes is further emphasized by utilizing conventional Li-host graphite anode for full cell assembly, attaining a record voltage of 3 V in an organic cathode Li-ion proof-of-concept cell.

Thiol-decorated covalent organic frameworks as multifunctional materials for high-performance supercapacitors and heterogeneous catalysis

This work highlights the importance of rational molecular design of COFs decorated with redox-active thiol moieties to confer them a multifunctional nature and to maximize their catalytic and electrochemical performances.

A robust redox-active hydrogen-bonded organic framework for rechargeable batteries

A robust HOF has been employed as cathode for LIBs. The decoration of rich redox-active moieties in HOFs introduces the surface-controlled capacitive mechanism in LIBs, accessing a high capacity, high rate capability and excellent cycling stability.

Quinone shuttling impels selective electrocatalytic alcohol oxidation: A hydrogen bonding-directed electrosynthesis

Electrochemical furfuryl alcohol oxidation to furfural impelled by quinones as electrocatalytic hydrogen shuttle mediators. • The analysis of the effect of 14 quinones in the electrocatalytic oxidation of furfuryl alcohol. • Potential of 3 ring quinones as electro-catalytic hydrogen shuttle mediators. • 3 ring quinones impel the selective oxidation of alcohol to aldehydes. Today development of efficient catalytic systems for selective oxidation of alcohols to aldehydes remains not only a major concern in basic chemistry research but also a significant challenge for the chemical industry. One promising green and sustainable approach to increase the selectivity as well as waste reduction and to minimize the use of toxic and/or hazardous substances is the development of selective electro-catalytic acceptorless dehydrogenation method. By that, it will be possible to facilitate catalyst recovery and reutilization as well as producing only hydrogen as the by-product. Quinones as principal redox-active moieties within natural organic materials play a key role in electron-transport processes of biological systems. Herein, by taking the oxidation of furfuryl alcohol (FA) in dimethyl sulfoxide (DMSO) as a model reaction, 14 quinone derivatives from 3 families (benzoquinones (BQs), naphthoquinones (NQs), and anthraquinones (AQs)) have been surveyed as a hydrogen acceptor mediators. We demonstrate that, only for three-member ring quinones such as 9,10-anthraquinone-2,6-disulfonic acid (AQDS), which are stable during electrocatalysis, a significant increase of the selectivity to furfural with addition of AQDS is achieved. The effect is assigned to strong intermolecular interaction between FA and quinone dianion (Q 2− ) with selective transformation to aldehyde its regeneration to quinone and hydrogen production over cathode surface. This study assesses and validates the potential of quinones as electrocatalytic hydrogen acceptor mediators to impel the selective oxidation of alcohol to aldehydes.

One-dimensional covalent organic framework—Carbon nanotube heterostructures for efficient capacitive energy storage

Covalent organic frameworks (COFs) with redox-active moieties are potential capacitive energy storage materials. However, their performance is limited by their poor electrical conductivity and sluggish ion diffusion in their nanopores. Herein, we report coaxial one-dimensional van der Waals heterostructures (vdWHs) comprised of a carbon nanotube (CNT) core and a pyrene–pyridine COF shell synthesized by an in situ wrapping method. The coaxial structure allows efficient electronic interaction between the CNT core and COF shell and improves the electrical conductivity significantly. It also improves electrolyte ion accesses to redox-active pyridine groups in the COF, resulting in excellent capacitive energy storage performance with a high specific capacitance of ∼360 F g−1, an excellent rate capability of ∼80%, and a good stability of 92% capacitance retention after 20 000 charge/discharge cycles. Our strategy opens the door to create other multi-dimensional vdWHs for various potential applications.

Tailor-made organic polymers towards high voltage aqueous ammonium/potassium-ion asymmetric supercapacitors

Engineering the polymers with electrochemical functionality is a topic of contemporary research towards developing lightweight and low-cost energy storage devices. In this study, a pair of organic polymers is successfully synthesized by coupling the redox-active moieties such as perylenetetracarboxylic diimide together through monosulfide and disulfide groups. The introduction of two different sulfide linkages in the polymeric chain yields two distinct morphologies due to the different structures of sulfide linkage groups. These polymers are tested as the electrode materials for supercapacitors in two different water-in-salt electrolytes. The interactions of K+/NH4+ ions with polymer electrodes are separately studied in 27 m potassium acetate (KAc) and 27 m ammonium acetate electrolytes. The polymer with monosulfide moieties shows better specific capacitance, rate capability, and cyclic stability in 27 m KAc compared to the one with disulfide moieties. In order to demonstrate the practical application, the asymmetric supercapacitors are fabricated by using the polymer and activated carbon as the negative and positive electrodes, respectively. The device with 27 m KAc delivers an energy density of 29.9 Wh kg−1 at the power density of 850 W kg−1 and exhibits 79% of the initial capacitance after 10,000 charge-discharge cycles at the current density of 2 A g−1.

Role of Antioxidant Moieties in the Quenching of a Purine Radical by Dissolved Organic Matter.

Dissolved organic matter (DOM) has been known to inhibit the degradation of trace organic contaminants (TrOCs) in advanced oxidation processes but quantitative understanding is lacking. Adenine (ADN) was selected as a model TrOC due to the wide occurrence of purine groups in TrOCs and the well-documented transient spectra of its intermediate radicals. ADN degradation in the presence of DOM during UV/peroxydisulfate treatment was quantified using steady-state photochemical experiments, time-resolved spectroscopy, and kinetic modeling. The inhibitory effects of DOM were found to include competing for photons, scavenging SO4•- and HO•, and also converting intermediate ADN radicals (ADN(-H)•) back into ADN. Half of the ADN(-H)• were reduced back to ADN in the presence of about 0.2 mgC L-1 of DOM. The quenching rate constants of ADN(-H)• by the 10 tested DOM isolates were in the range of (0.39-1.18) × 107 MC-1 s-1. They showed a positive linear relationship with the total antioxidant capacity of DOM. The laser flash photolysis results of the low-molecular-weight analogues of redox-active moieties further supported the dominant role of antioxidant moieties in DOM in the quenching of ADN(-H)•. The diverse roles of DOM should be considered in predicting the abatement of TrOCs in advanced oxidation processes.

New insights into the mechanisms underlying biochar-assisted sustained high-efficient co-digestion: Reducing thermodynamic constraints and enhancing extracellular electron transfer flux

To clarify the roles of biochar in the anaerobic co-digestion of waste activated sludge (WAS) and food waste (FW), batch tests were conducted coupled with thermodynamics, extracellular electron transfer flux and microbial community analysis. Compared with the control group, biochar significantly facilitated the co-digestion at three periods, but its sustainable facilitation was mainly in the syntrophic methanogenesis of volatile fatty acids (VFAs). The thermodynamic analysis confirmed that biochar could alleviate limitations imposed by high hydrogen partial pressure during interspecies hydrogen transfer (IHT), the thermodynamic windows was expanded 137% and 92% in the syntrophic methanogenesis of acetate and propionate, respectively. Meanwhile, due to the redox capacity of biochar (4.85 and 0.35 μmol e−/g biochar), the equivalent current of direct interspecies electron transfer (DIET) flux for syntrophic methanogenesis of acetate and propionate obtained were 1.0 × 10−4 A and 0.9 × 10−4 A, which were 108 times than that of IHT. It should be noticed that the functional microorganisms like Methanosarcina which could participate DIET were only enriched on the surface of biochar, the dominant Methanothermobacter in suspended sludge probably indicate IHT was still the main pathway for syntrophic methanogenesis. Nevertheless, the DIET triggered by the redox-active moieties on the surface of biochar and the enhanced IHT by alleviating thermodynamic restrictions, promoted the syntrophic methanogenesis synergistically.

Step Toward Eco-Friendly Green Source of Non-Aqueous Electrolytes for Redox Flow Battery

The efficient utilization of energy from non-exhaustive resources without adverse effects on the environment is a way forward for the sustainable development of society. The intermittent nature of renewable energy from non-exhaustive resources such as solar, wind, etc., requires a large-scale and advanced energy storage system to eliminate the impact of intermittency on the power grid. Redox flow battery (RFB) technology is one of the promising candidates for large-scale grid systems. Present commercial RFB technology is based on the redox reactions of electroactive metals, which are constrained by material abundance, cost, and environmental issues. These issues are prompting scientists to look into organic-based technologies as potential metal-free battery alternatives. Organic-based materials offer structural diversity of organic molecules to adjust the electrolyte materials' thermodynamics and redox characteristics, in addition to low cost and scalability. This opens the door to the development of green and sustainable energy storage devices.Despite development over the last decade, organic compound exploitation for RFB remains limited. Organics with limited ionic conductivity and poorly defined conducting channels have poor voltage efficiency and cyclability. In aqueous flow batteries, the cell potential is also limited by the electrolysis of water. The scientific community, on the other hand, is addressing this issue by introducing the non-aqueous RFB (NAqRFB).Quinones are the most redox-active moieties found in natural organic materials, and they play a critical role in biological electron transport. They are a class of molecules that are formed from aromatic compounds like benzene or naphthalene and have a fully conjugated cyclic diketone structure with a redox reaction based on the rearrangement of the conjugated double bond. 1,4-naphthoquinone (NQ) is investigated as a possible negolyte candidate. NQ as metal-free organic negolyte was coupled with metal acetylacetonate-based posolytes, M(acac), where M = Cr, V, Mn. Both types of redox species (metal & metal-free) have good solubility in the solvent - Dimethylacetamide (DMA) - and ionic conductivity was enhanced using the supporting electrolyte of TEABF4. Cyclic voltammetry (CV) analysis using glassy carbon working electrode (GCE) highlighted that NQ offers reversibility; the high value of negative redox potential -1.75 V vs. Ag/Ag+ enables higher cell potential and posses no irreversible side reactions.The electrochemical stability of the negolyte was further tested using the symmetrical cell having an electrolyte of 0.06 M concentration of NQ as redox species. The electrolyte flow from the reservoir, cathode, and anode in a series arrangement. The redox species are reduced at the cathode and then oxidized at the anode, which helps maintain the state-of-charge (SOC) at 50 %. The cell was operated for 50 cycles at the C-rate = 1C, i.e., 2.75 mA⋅cm-2 at the cutoff potentials of ±0.3 V. The energy efficiency of that symmetric cell was 99.7 %, and discharge capacity retention was 99.967%. These results are validated from the reported study by Yu Ding, 2016. This strengthen the motivation of using the NQ as metal-free organic negolyte for single NAqRFB-cell. The insertion of the mentioned metals (Cr, V, Mn) at the posolyte while keeping NQ ion at the negolyte ensured the generation of novel chemistries for NAqRFBs, in detail NQ||Cr, NQ||V, and NQ||Mn, with cell potential differences of 3.25 V, 2.2 V, and 2.45 V, respectively.Detailed characterization was performed using polarization, EIS, and charge-discharge cycling (CDC) – Table 1. Post-mortem CVs of the electrolyte using GCE highlight the stability of the electrolyte after intensive CDC. The RFB assembled with NQ||Cr offered the highest capacity and energy density. However, it was faced with lower energy efficiency. The post-mortem analyses on the posolyte signify that there was crossover through the membrane, which ended up with a contaminated electrolyte (mixture with negolyte chemistry) that affected the extended capacity of the cell. The RFB composed of NQ||V offers the 2nd highest capacity and energy density than others and is two times more than reported V||V NAqRFB. Reinforced membranes permit to decrease the permeability of the membrane toward smaller ions of NQ as compared to V2+ redox ions. Furthermore, the NQ||Mn battery demonstrated a stable performance up to 25 cycles having higher efficiencies and with a decent energy density of ca. 60 mWh.g-1 . NQ has high solubility of 1.5 M in DMA and future work at higher capacities is in progress for in-depth study covering other aspects. The study may ascertain the feasibility of NQ-based RFB to be the eco-friendly green alternate battery chemistry. Figure 1

Viologen-Immobilized 2D Polymer Film Enabling Highly Efficient Electrochromic Device for Solar-Powered Smart Window.

Electrochromic devices (ECDs) have emerged as a unique class of optoelectronic devices for the development of smart windows. However, current ECDs typically suffer from low coloration efficiency (CE) and high energy consumption, which have thus hindered their practical applications, especially as components in solar-powered EC windows. Here, the high-performance ECDs with a fully crystalline viologen-immobilized 2D polymer (V2DP) thin film as the color-switching layer is demonstrated. The high density of vertically oriented pore channels (pore size ≈ 4.5nm; pore density ≈ 5.8 × 1016 m-2 ) in the synthetic V2DP film enables high utilization of redox-active viologen moieties and benefits for Li+ ion diffusion/transport. As a result, the as-fabricated ECDs achieve a rapid switching speed (coloration, 2.8 s; bleaching, 1.2 s), and a high CE (989 cm2 C-1 ), and low energy consumption (21.1 µW cm-2 ). Moreover, it is managed to fabricate transmission-tunable, self-sustainable EC window prototypes by vertically integrating the V2DP ECDs with transparent solar cells. This work sheds light on designing electroactive 2D polymers with molecular precision for optoelectronics and paves a practical route toward developing self-powered EC windows to offset the electricity consumption of buildings.

Immobilizing Redox-Active Tricycloquinazoline into a 2D Conductive Metal-Organic Framework for Lithium Storage.

Heteroaromatic-conjugated aromatic molecules have inspired numerous interests in rechargeable batteries like Li-ion batteries, but were limited by low conductivity and easy dissolution in electrolytes. Herein, we immobilize a nitrogen-rich aromatic molecule tricycloquinazoline (TQ) and CuO4 unit into a two-dimensional (2D) conductive metal-organic framework (MOF) to unlock their potential for Li+ storage. TQ was identified redox activity with Li+ for the first time. With a synergistic effect of TQ and CuO4 unit, the 2D conductive MOF, named Cu-HHTQ (HHTQ=2,3,7,8,12,13-hexahydroxytricycloquinazoline), can facilitate the Li+ /e- transport and ensure a resilient electrode, resulting in a high capacity of 657.6 mAh g-1 at 600 mA g-1 with extraordinary high-rate capability and impressive cyclability. Our findings highlight an efficient strategy of constructing electrode materials for energy storage with combining multiple redox-active moieties into conductive MOFs.