Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries

Open AccessCCS ChemistryRESEARCH ARTICLES22 Dec 2022Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries Xu Liu, Xuri Zhang, Chaoyu Bao, Zengrong Wang, Heng Zhang, Guoping Li, Ni Yan, Ming-Jia Li and Gang He Xu Liu Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710049 Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710054 , Xuri Zhang Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710054 , Chaoyu Bao School of Materials Science and Engineering, Engineering Research Center of Transportation Materials, Ministry of Education, Chang'an University, Xi'an, Shaanxi Province 710064 , Zengrong Wang Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710054 , Heng Zhang Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710054 , Guoping Li Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710049 , Ni Yan School of Materials Science and Engineering, Engineering Research Center of Transportation Materials, Ministry of Education, Chang'an University, Xi'an, Shaanxi Province 710064 , Ming-Jia Li Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710049 and Gang He *Corresponding author: E-mail Address: [email protected] Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710049 Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi Province 710054 https://doi.org/10.31635/ccschem.022.202202336 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Two-electron neutral aqueous organic redox flow batteries (AORFBs) hold more promising applications in the power grid than one-electron batteries because of their higher capacity. However, their development is strongly limited by the structural instability of the highly reduced species. By combining the extended π-conjugation structure of the anolytes and the enhanced aromaticity of the highly reduced species, we reported a series of highly conjugated and inexpensive arylene diimide derivatives ( NDI, PDI, and TPDI) as novel two-electron storage anolyte materials for ultrastable AORFBs. Matched with (ferrocenylmethyl)trimethylammonium chloride ( FcNCl) as catholyte, arylene diimide derivative-based AORFBs showed the highest stability in two-electron AORFBs to date. The NDI/ FcNCl-based AORFB delivered 98.44% capacity retention at 40 mA cm−2 for 350 cycles; TPDI/FcNCl-based AORFB also showed remarkable stability with 97.22% capacity retention at 20 mA cm−2 over 200 cycles. This finding lays the theoretical foundation and offers a reference for improving the stability of two-electron AORFBs. Download figure Download PowerPoint Introduction Currently, the imbalance between energy supply and demand has become increasingly prominent in the process of global economic development.1–3 Therefore, improving the storage and utilization efficiency of new energy (wind or solar) has attracted much attention.4–6 Flow batteries stand out in large-scale storage technology and have been applied to electricity grids due to the decoupled energy and power, scalability (up to MW/MWh), and security.7–9 Among them, neutral aqueous organic redox flow batteries (AORFBs) are expected to become the leader in next-generation energy storage and conversion devices, resulting from their high conductivity, safety, flexibility, environmental friendliness, and low cost.10–15 Electrolyte materials are the key points for neutral AORFBs.16,17 The energy source of existing electrolyte materials mainly relies on variable valence states such as C=O, C=N, N=O, and metals. The active materials, including arylene diimides,18,19 quinones,20,21 viologens,22–24 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO),25–28 ferrocenes,29–32 and so on,33–35 have excellent redox properties and high water solubility, rendering them very suitable for neutral AORFBs. Viologen has been widely used as an electrolyte material for neutral AORFBs.36–41 Viologens are mostly used for one-electron storage due to the lack of stability of highly reduced species.42 Therefore, improving the effective electron utilization and stability of viologen has become an important challenge in the application of neutral AORFBs.43 In recent years, some research groups have made many efforts to expand the conjugated structure and electron delocalization of viologen by introducing electron donor groups such as thiazolo[5,4-d]thiazole,44 phenyls,45 and thiophene.46 The results proved that this strategy effectively stabilized the highly reduced species. However, the capacity retention is still less than 90% in 300 cycles, which is due to the pyridinium rings changing from aromaticity [NICS(1) = −9.28] (NICS = nucleus-independent chemical shift) to antiaromaticity [NICS(1) = 2.73], resulting in the decline of stability. Therefore, it is necessary to develop a new electrolyte material with a more stable structure for highly reduced species to achieve efficient two-electron storage stability. Arylene diimide derivatives have more conjugated planar rigid structures than viologens, including strong π–π conjugation and weak p–π conjugation, beneficial for promoting redox activity and electron transfer.47–53 In different redox states, these derivatives maintain good aromaticity and high stability.54 Moreover, their excellent photoelectrochemical properties, such as two-electron transfer, strong visible light absorption, photostability, and thermal stability, make them widely used in organic batteries,55–58 pseudocapacitors,59 optoelectronic devices,60 biosensing,61 and other applications. Recently, arylene diimide derivatives have also been used as electrolyte materials for flow batteries.62–64 Jin and coworkers reported an all-polymer particulate slurry redox flow battery using a microsized and uniformly dispersed all-polymer particulate suspension. The discharge capacity retention after 300 cycles was 70% of the initial capacity, and the capacity utilization was only a poor value of 9.23%.65 Byon and coworkers demonstrated a potassium salt of N,N′-bis(glycinyl)naphthalene diimide [ K2-BNDI], which showed a poor solubility of 30 mM in water. 0.025 M [ K2-BNDI]/ 4-OH-TEMPO AORFB delivered 83.2% capacity retention at 5 mA cm−2 in 100 cycles.66 The results indicated that the existing arylene diimide-based electrolytes have certain two-electron transfer properties. However, they still have many challenges such as insufficient stability and poor water solubility. Thus, it could be envisioned that the extension of the π-conjugated structure and the decoration of more hydrophilic groups with large sizes into hydrophobic arylene diimide derivatives such as different numbers (2∼6) of hydrophilic ammonium cation groups, should significantly enhance the structural stability, as well as increase the solubility of the active materials. This method would improve the charge repulsion between the pendent ammonium groups, prevent the dimerization degradation process, and inhibit electrolyte penetration.67 Based on these considerations, a series of inexpensive and high-yield quaternary ammonium salt-containing arylene diimide derivatives ( NDI, PDI, and TPDI) with narrow bandgap, and stable π-conjugate structure were synthesized as anolytes for AORFBs. Density functional theory (DFT) calculations showed that the aromaticity of arylene diimide derivatives was further enhanced from oxidized to highly reduced species. The larger molecular size achieved zero penetration for 30 days. Using (ferrocenylmethyl)trimethylammonium chloride ( FcNCl) as the catholyte, this work delivered excellent ultrastability for two-electron storage with a low daily decay and Coulombic efficiency (CE) close to 100%. Compared with previous work, our current approach demonstrated much better battery performance and was the most stable system for two-electron storage. Experimental Methods NMR spectra were collected using a Bruker 400 MHz NMR spectrometer (Bruker, Zurich, Switzerland). UV–vis measurements were performed using a DH-2000-BAL Scan spectrophotometer (OceanOptics, Florida, USA). Cyclic voltammetry (CV) in solution was measured using a potentiostat model CHI660E B157216 (CH Instruments, Inc., Beijing, China). The Linear sweep voltammetry (LSV) was measured on a rotating disk electrode (RDE) device (Pine Instruments Co. (North Carolina, USA; 0.1963 cm2). The conductivity was measured using a conductivity meter (DDSJ-308A, Ningbo Hinotek Technology Co., Ltd., Zhejiang, China). Electrochemical impedance analysis (EIS) was performed using an Autolab electrochemical workstation (AUT86797-302N, Metrohm Instruments, Herisau, Switzerland). High-resolution mass spectra (HRMS) were collected on a Bruker maXis UHR-TOF mass spectrometer (Bruker Scientific Technology Co., Ltd., Beijing, China) in electrospray ionization (ESI) positive mode. Electron paramagnetic resonance (EPR) was measured using a Bruker A300-9.5/12 instrument (Bruker Scientific Technology Co., Ltd., Beijing, China) at room temperature in dry degassed methanol. The EPR parameters for the experiments are as follows: modulation frequency = 100 kHz, modulation amplitude = 1.0 G, time constant = 81.92 ms, conversion time = 80.00 m, center field = 3514.503 G, sweep width = 1000 G, microwave attenuation = 26.3 dB, microwave power = 0.00471 mW. All battery tests were conducted under an Ar atmosphere. The flow battery was tested at room temperature (RT) on a battery tester (NEWARE instrument, CT-4008T-5V12A-S1-F, Shenzhen, China). All photographs were taken using a Nikon D5100 digital camera. Both AMV and DSV anion exchange membrane were purchased from Wuhan Zhisheng New Energy Co., LTD. (Wuhan, China), with film thickness (130 μm, 100 μm), tensile strength (0.16 MPa, 0.14 MPa), pore diameter (1∼3 nm), and area-specific resistance (2.8 Ω cm2, 1.1 Ω cm2 for 0.5 M NaCl). Synthesis of NDI The cationic naphthalene diimide derivative NDI was synthesized following the previous literature procedure ( Supporting Information Scheme S1).68 Briefly, 1,4,5,8-naphthalene tetracarboxylic dianhydride ( NTDA) (1 g, 3.73 mmol) was dissolved in 120 mL dry toluene under N2 atmosphere and heated to 90 °C, and N,N-dimethyl-1,3-propanediamine (3 mL, 23.84 mmol) was added dropwise over 10 min. The reaction mixture was heated at 120 °C for 24 h. The crude mixture was concentrated on a rotary evaporator, and the yellow crystalline NDI-N was purified by recrystallizing from ethanol. Yield: 1 g (61%). A mixture of NDI-N (1 g, 2.29 mmol), 5 mL methyl chloride (1.0 mol L−1 in tetrahydrofuran [THF]), and 50 mL dry dimethylformamide (DMF) were added. The solution was sealed in a pressure vial with a Teflon bushing and heated at 85 °C for 12 h. The resulting suspension was cooled, collected by vacuum filtration, washed with DMF, acetone, and ether, and then dried in a vacuum at 60 °C overnight to give a gray solid NDI product. Yield: 1.1 g (89%). 1H NMR (400 MHz, D2O, δ): 8.60 (S, J = 2.4 Hz, 4H), 4.23 (t, J = 6.9 Hz, 4H), 3.57–3.48 (m, 4H), 3.14 (s, 18H), 2.32–2.22 (m, 4H). 13C NMR (101 MHz, D2O, δ): 163.47, 131.00, 125.57, 125.46, 63.95, 52.96, 37.70, 21.38. HRMS (ESI) m/z: [M−2Cl]2+ calcd for C26H34N4O4, 233.1285; found, 233.12779. Synthesis of PDI The cationic perylene diimide derivative PDI was synthesized following the literature procedure ( Supporting Information Scheme S2).69 3,4,9,10-Perylenetetracarboxylic dianhydride ( PTCDA) (2 g, 5.10 mmol) and N,N-dimethyl-1,3-propanediamine (6 mL, 47.68 mmol) were dissolved in 80 mL dry isobutanol and heated at 90 °C for 24 h with stirring under N2 atmosphere. The crude product was filtered and washed with deionized water and ethanol. The obtained residue was treated with 5% aqueous NaOH solution at 90 °C for 30 min to remove the unreacted raw material. The suspended mixture was filtered, washed with water and ethanol, and dried under vacuum to give the product a red solid PDI-N. Yield: 2.6 g (90%). To a mixture of PDI-N (2 g, 3.57 mmol), 8 mL methyl chloride (1.0 mol L−1 in THF), and 150 mL dry toluene were added. The solution was sealed in a pressure vial with a Teflon bushing and heated at 105 °C for 12 h. The resulting suspension was cooled, collected by vacuum filtration, washed with toluene, and ether, and then dried in a vacuum at 60 °C overnight to give a brownish-red PDI product. Yield: 2.2 g (93%). 1H NMR (400 MHz, CF3COOD, δ): 8.94 (s, 8H), 4.62 (s, 4H), 3.81 (s, 4H), 3.37 (s, 18H), 2.61 (s, 4H). 13C NMR (101 MHz, CF3COOD, δ): 165.93 (s), 136.37 (s), 133.24 (s), 129.41 (s), 126.44 (s), 124.48 (s), 121.85 (s), 64.88 (s), 53.22 (s), 37.92 (s), 21.84 (s). HRMS (ESI) [M−2Cl]2+ calcd for C36H38N4O4, 295.1441; found, 295.14421. Synthesis of TPDI Compound TPDI was synthesized according to a previous procedure in the literature ( Supporting Information Scheme S3).70 PTCDA (1.62 g, 4.13 mmol) and N,N-dimethyl-1,3-propanediamine (30 mL, 201 mmol) were added, mixed, and heated at 100 °C for 28 h, then the temperature was gradually increased to 170 °C for over 4 h. Then the mixture was cooled to room temperature and a mixture of ethanol and diethyl ether (1:3) was added. The resulting precipitate was collected by suction filtration, washed with diethyl ether, and dried under a vacuum to obtain a red solid TPDI-N. Yield: 2.4 g (90%). To a mixture of TPDI-N (1.38 g, 2.13 mmol), water (6 mL), 85% formic acid (6.4 mL), and 30% formaldehyde (4.4 mL) were added. The solution was stirred at room temperature for 1 h and then heated at 120 °C for 16 h. Caution: During this time, the mixture produced a lot of carbon dioxide, so slow deflation was required after the reaction. The solution was cooled to room temperature, then precipitated with ethyl ether, and centrifuged (8000 rpm for 5 min at 25 °C). The residue was dried under a vacuum, obtaining their tertiary amine analogue TPDI-MN, a red solid. Yield: 1.9 g (86%). A mixture of TPDI-MN (1.5 g, 1.45 mmol), dry MeOH (60 mL), and Na2CO3 (1 g) was stirred at room temperature for 12 h, then added methyl iodide (3 mL, 48.19 mmol), and heated at 60 °C for 12 h. The mixture was cooled to room temperature, then precipitated with ethyl ether. The resulting precipitate was collected by suction filtration, washed with diethyl ether, and dried under a vacuum. The product was exchanged for chloride by column anion exchange with Amberlite® IRA-900 chloride from anion exchange resin to give a red solid TPDI. Yield: 1.39 g (90%). 1H NMR (400 MHz, CF3COOD, δ): 8.95 (dd, J = 8.1 Hz, 8H), 5.10 (s, 4H), 4.56 (s, 20H), 4.35 (s, 8H), 3.60 (s, 36H). 13C NMR (101 MHz, CF3COOD, δ): 167.80 (s), 136.82 (s), 133.39 (s), 129.63 (s), 126.73 (s), 124.66 (s), 121.57 (s), 54.43 (s), 53.64 (s), 52.02 (s), 49.62 (s), 44.23 (s), 35.56 (s). HRMS (ESI) [M−3Cl]2+ calcd for C50H74N8O4, 283.5272; found, 283.52952. Synthesis of [(NPr)2V]Cl4 Compound [(NPr)2V]Cl4 was synthesized according to the literature.22 In a 250 mL N2 purged Schlenk flask, 4,4′-bipyridine (2.0 g, 12.8 mmol) was combined with (3-bromopropyl)trimethylammonium bromide (10 g, 38.3 mmol) in 15 mL of dimethyl sulfoxide (DMSO) and stirred at 100 °C for 3 h. The resulting precipitate was collected by suction filtration and washed with cold DMSO and acetonitrile. The product was exchanged for chloride by column anion exchange with Amberlite® IRA-900 chloride form anion exchange resin to give a white solid [(NPr)2V]Cl4. Yield: 4.48 g (70%). 1H NMR (400 MHz, D2O, δ): 9.09 (s, 2H), 8.51 (s, 2H), 4.74 (s, 2H), 3.47 (d, J = 4.4 Hz, 2H), 3.08 (d, J = 2.3 Hz, 9H), 2.57 (s, 2H). Synthesis of FcNCl FcNCl was synthesized according to a reported method.71 (Ferrocenylmethyl)dimethylamine (10 g, 41.2 mmol), methyl chloride (49.4 mL, 445.3 mmol), and 25 mL dry CH3CN were added to a round-bottom flask, which was stirred at RT overnight. The product was collected by filtration, washed three times with 10 mL ether, and dried under a vacuum to obtain a yellow solid FcNCl product. Yield: 10.9 g (90%). 1H NMR (400 MHz, D2O, δ): 4.49 (t, J = 1.8 Hz, 2H), 4.40 (t, J = 1.8 Hz, 2H), 4.37 (s, 2H), 4.25 (s, 5H), 2.92 (s, 9H). Computational methods We performed simulations of the experiments to confirm the conformation of the oxidized products via predictions of UV-vis spectroscopy of the compounds in water to resolve their properties. We employed the Polarizable Continuum Model (PCM) as a self-consistent reaction field (SCRF) for the calculation of their equilibrium geometries, vibrational frequencies, vertical excitation energies and the corresponding absorption wavelengths. The geometries for the ground state of these compounds were optimized at the B3LYP hybrid functional and 6-311+G(d) basis set for all atoms.37 The structures of all stationary points were characterized as true minima on the potential energy surface from a vibrational frequencies analysis in which imaginary modes were absent. Using the optimized ground-state equilibrium geometries in water solution as starting points, the absorption wavelengths (λTD-DFT), oscillator strength (f), molecular orbitals (MOs) were calculated with the non-equilibrium time-dependent Density Functional Theory (TD-DFT) framework. The same functional and basis set was employed in the optimization calculations. All of the above DFT and TD-DFT calculations reported in this work were performed using the Gaussian 09 code.23,72 The volume was estimated using Marching Tetrahedron (MT) mothed, based on the vdW surface defined by ρ = 0.001 au isosurface, using the Multiwfn code.73 NMR chemical shifts for Nucleus-independent chemical shift (NICS)74,75 values were calculated at the points shown using the GIAO76 method. Result and Discussion Synthesis and structure characterization The designed arylene diimide derivatives, NDI, PDI, and TPDI, were synthesized according to the previous literature (Scheme 1).68,70 First, NTDA and PTCDA underwent a ring-opening reaction, then reacted with an amino group to form amides and subsequently, imides by the closed-loop reaction. Then methyl chloride was introduced to produce highly hydrophilic naphthalene diimide ( NDI) and perylene diimide ( PDI) via ionization. The methylation reaction of TPDI is different from NDI and PDI. The amino group reacted with excess formic acid and formaldehyde to obtain tertiary amines by Eschweiler–Clarke reaction, and further got quaternary ammonium salt product with methyl iodide. Among them, the solubility of NDI in 2 M NaCl solution is as high as 1.00 M, corresponding to a theoretical capacity of 53.6 Ah L−1. Expanding only the conjugation resulted in the solubility of PDI of 0.08 M. Further improvement of the solubility by introducing more hydrophilic ammonium cation groups to prepare TPDI, yielded a solubility of 0.14 M, approximately twice that of PDI ( Supporting Information Figure S1). The solubility and capacity information of NDI/ PDI/ TPDI are summarized in Supporting Information Table S1. The molecular structures were verified by NMR and HRMS. The and calculated values of UV–vis absorption spectra were ( Supporting Information Compared with NDI the absorption of PDI and TPDI showed a bandgap, an and absorption in the visible Scheme 1 The of arylene diimide Download figure Download PowerPoint Electrochemical characterization The electrochemical properties of NDI/ PDI/ TPDI redox were characterized by and Supporting Information Figure Figure the structural of the arylene diimide derivatives the redox NDI an two-electron at = ( = ( PDI also redox at = ( = ( TPDI one-electron and two-electron with redox of = ( = ( due to the of the and electron The redox of PDI and TPDI were significantly than that of The potential between the redox of NDI/ PDI/ TPDI gradually from to to which was to the increased conjugation and more The current of NDI was significantly higher than that of PDI and TPDI, which was by the solubility The better the solubility of the the the the conductivity was resulting in an increased of effective charge The of redox of NDI, PDI, and TPDI showed a with the of that all redox were and with FcNCl as the the NDI/ PDI/ FcNCl-based AORFBs delivered and battery them as anolytes to improve the energy of batteries in of different NDI/ PDI/ TPDI showed good with a of redox excellent redox and stability. Figure 1 Cyclic of mM NDI, PDI, TPDI, and FcNCl with in 0.5 M NaCl The reaction structure of the arylene diimide Download figure Download PowerPoint Electrochemical characterization was used to the electrochemical of NDI/ PDI/ TPDI ( Supporting Information The and electron transfer constant for the process are and cm2 and and the process, and are cm2 and The transfer constant of NDI/ PDI/ TPDI was high to flow batteries with low and DFT calculations DFT calculations were to confirm the conformation of the oxidized NDI PDI and TPDI and reduced NDI PDI and TPDI The oxidized NDI PDI and TPDI demonstrated excellent with a strong π-conjugated rigid planar and narrow of and the electron transfer of the was and a new π–π conjugated was The were and which are to the electron transfer of the The results are shown in Supporting Information Figure that the were well the center system and by the ammonium further proved that diimide derivatives are a of stable electrolyte material. for the stability of arylene diimide derivatives is The results to the same the pyridinium rings of are they are in This from to be an important for the instability of [(NPr)2V]Cl4 two-electron storage. In NDI the naphthalene was [NICS(1) = and the diimide rings were [NICS(1) = In NDI all the rings [NICS(1) = In PDI the was [NICS(1) = the rings that form the naphthalene were [NICS(1) = and the diimide rings were [NICS(1) = In PDI all rings are [NICS(1) = The results for TPDI are very to for PDI. The values showed that the of their aromaticity is TPDI PDI NDI corresponding to molecular stability. Moreover, their molecular are calculated as and which is beneficial for the penetration of The of the electrolyte for the membrane Engineering Co., was tested by for 30 and and were in the by UV–vis that ( Supporting Information Figure important be the of and π–π which further increased the between and the of Figure 2 molecular molecular and of NDI NDI PDI PDI TPDI and TPDI by DFT calculations. of aromaticity of NDI, PDI, and TPDI from the oxidized to the highly reduced species. The red enhanced the red reduced aromaticity still the enhanced The of the rings is used to the aromaticity of a and all values are Download figure Download PowerPoint In UV–vis spectra The in UV–vis spectra were to the two-electron transfer process and conjugation of these batteries By different the UV–vis spectra of different molecular states were NDI nm), the initial absorption of NDI to be in the mainly at and an applied potential of NDI an electron and the species NDI The absorption of the visible light was and a was at The of the anolyte from to the is increased to NDI the reduced NDI The absorption was enhanced at and and the of the anolyte PDI and TPDI the same Compared with NDI, the visible light absorption of PDI and TPDI showed an which have been by increased The absorption of the oxidized state PDI in the visible was mainly at and the to the species PDI to and the increased to the absorption of reduced PDI increased at and Compared with PDI, TPDI in absorption in the visible and due to the The absorption of the oxidized state TPDI is mainly at and in the visible the increased to the absorption of the species TPDI was at and the absorption of reduced TPDI was at and the increased to diimide materials, the increased absorption and the of absorption were by