Pore Size-Tuned Graphene Oxide Framework as ... - ACS Publications

Subscriber access provided by Kaohsiung Medical University

Communication

Pore Size-Tuned Graphene Oxide Framework as Ion-Selective and Protective Layers on Hydrocarbon Membranes for Vanadium Redox Flow Batteries Soohyun Kim, Junghoon Choi, Chanyong Choi, Jiyun Heo, Dae Woo Kim, Jang Yong Lee, Young Taik Hong, Hee-Tae Jung, and Hee-Tak Kim Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b01429 • Publication Date (Web): 03 May 2018 Downloaded from http://pubs.acs.org on May 3, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Pore Size-Tuned Graphene Oxide Framework as Ion-Selective and Protective Layers on Hydrocarbon Membranes for Vanadium Redox Flow Batteries Soohyun Kim,†,§ Junghoon Choi,† § Chanyong Choi,† Jiyun Heo,† Dae Woo Kim,† Jang Yong Lee,‡ Young Taik Hong,‡ Hee-Tae Jung,*,† and Hee-Tak Kim*,† †

Department of Chemical and Biomolecular Engineering, KAIST Institute for the Nanocentury,

Korea Advanced Institute of Science and Technology, 291, Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea ‡

Center for Membrane, Korea Research Institute of Chemical Technology, 141, Gajeong-ro, Yuseong-gu, Daejeon, Republic of Korea

ABSTRACT: The laminated structure of graphene oxide (GO) membranes provides exceptional ion separation properties, due to the regular interlayer spacing (d) between laminate layers. However, a larger effective pore size of the laminate immersed in water (~11.1 Å) than the hydrated diameter of vanadium ions (> 6.0 Å) prevents its use in vanadium redox flow battery (VRFB). In this work, we report an ion-selective graphene oxide framework (GOF) whose d is tuned by cross-linking the GO nanosheets. Its effective pore size (~5.9 Å) excludes vanadium

ACS Paragon Plus Environment

1

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

ions by size but allows proton conduction. The GOF membrane is employed as a protective layer to address the poor chemical stability of sulfonated poly(arylene ether sulfone) (SPAES) membranes against VO2+ in VRFB. By effectively blocking vanadium ions, the GOF/SPAES membrane exhibits 4.2 times lower vanadium ion permeability and five times longer durability compared with the pristine SPAES membrane. Moreover, the VRFB with the GOF/SPAES membrane achieves an energy efficiency of 89% at 80 mA cm-2 and a capacity retention of 88% even after 400 cycles, far exceeding Nafion 115, and demonstrating its practical applicability for VRFB.

KEYWORDS: graphene oxide framework membranes, vanadium redox flow batteries, pore size exclusions, hydrocarbon membranes, chemical stabilities

Demand for large-scale energy storage is increasing due to efforts to improve the reliability and quality of intermittent renewable energy sources.1-2 Among approaches for large-scale energy storage, redox flow batteries have attracted significant attention because of their technical advantages, including safety and independent scaling of power and energy ratings. In particular, the vanadium redox flow battery (VRFB) is regarded as one of the most promising candidates because of its advanced efficiency, high reliability, and the absence of cross-contamination. Recent demonstrations of kW to MW scale VRFB systems have confirmed the validity of the VRFB technology.3 Membranes which can prevent the mixing of positive and negative active materials but still allow proton conduction are essential for VRFB performance. To minimize power and energy losses, these require high ion conductivity and low vanadium ion permeability, as well as good


2

Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

chemical stability and low cost. Perfluorinated cation exchange membranes such as Nafion have been conventionally used for VRFBs because of their high proton conductivity and good chemical stability. However, the high cost and low proton (H+)/vanadium ion (Vn+) selectivity of Nafion impedes their wide-spread use in VRFB, and has motivated the development of cheaper and more ion-selective alternatives.4-6 Among those, hydrocarbon-based ion exchange membranes (HC membrane) has been highly attractive candidate due to its low cost and high ion selectivity.7-8 However, HC membranes are vulnerable to chemical degradation by the highly oxidative VO2+ ion, which lowers their competitive value.9-11 Recently, a number of efforts have been made to overcome the poor chemical stability of the HC ion-exchange membrane by either modifying its chemical structure of ionomers or introducing a protective layer. Structurally modified ion exchange membranes have shown improved chemical stability, however, their complex synthesis and insufficient stability limit their usage.12-15 On the other hand, the protective layer approach is promising because it allows the use of various low cost HC membranes.16-17 In our previous work,18 we fabricated a HC/Nafion bilayer membrane with a mechanical nano-fastener, where the Nafion layer protected the HC membrane from VO2+ ions. However, because of the high vanadium ion permeability of the Nafion protection layer, VO2+ ions reached the HC membrane, eventually causing delamination of the Nafion layer from the HC membrane. Yu et al. proposed a poly(tetrafluoroethylene) (PTFE) sandwiched sulfonated poly(ether ether ketone) (SPEEK) membrane.19 But while the porous PTFE film can improve the mechanical stability of the SPEEK membrane, it cannot stop the chemical degradation during cycling. Therefore, the development of a protective layer with higher VO2+ blocking is still needed.


3

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 24

The graphene oxide (GO) membrane is a collection of GO nanosheets with an interlocking layered structure, and has recently attracted a great deal of interest due to its molecular separation properties and potential for industrial-scale production.20-23 The precise molecular sieving of the GO membrane is produced by the size exclusion of the interlayer spacing, d, between the GO nanosheets; ions with hydrated radii larger than the GO nanochannel are blocked, whereas smaller ions permeate through the interlayer spacing. Furthermore, the smaller ions experience ultrafast transport through the GO membrane, thousands of times faster than simple diffusion, due to a capillary-like force, which further strengthens its practical potential.22 These outstanding separation properties of the GO membrane can be exploited for electrochemical energy storage, as evidenced by the recent work on the suppression of polysulfide shuttle by a GO membrane for a lithium sulfur battery.24-26 To expand the applications of the GO membrane, it is critical to tune the effective pore size of the GO membrane for each application. A graphene oxide framework (GOF), which is derived from GO by introducing cross-linkers between the GO nanosheets, provides a versatile platform for tunable ion selectivity. By adjusting the length of the cross-linker, d can be controlled. GOFs with cross-linkers have been applied to gas separation and ion dialysis.27-29 The strong ion selectivity of the GOF motivated us to exploit it as a membrane component for VRFB. When the effective pore size of the GOF is between the hydrated size of vanadium ions and a proton, the GOF membrane is permeable to protons but blocks vanadium ions, as illustrated in Figure 1. The previously reported extraordinary fast proton conduction of GO also suggests it may be possible to achieve low membrane resistance with the GOF membrane.30-31 Based on these considerations, we designed an ion-selective GOF membrane as a protective layer to improve the chemical stability of the HC membrane for VRFB application. As a proof-


4

Page 5 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

of-concept, a GOF membrane with a target pore size was prepared using a crosslinking method, and was then combined with a sulfonated poly(arylene ether sulfone) (SPAES) membrane to form a GOF/SPAES membrane. The GOF membrane was found to not only protect the SPAES membrane from the oxidative VO2+ but also enhanced the vanadium ion selectivity of the GOF/SPAES membrane. The cycling stability of the VRFB was enhanced up to five times with the introduction of the GOF layer, and the energy efficiency of the GOF/SPAES membrane was even higher than that of a Nafion membrane. Based on these results, the GOF membrane offers strong benefits for achieving advanced VRFBs.

Figure 1. Schematics of the selective ion transfer of hydrated vanadium ions and protons in the GOF membrane, and the molecular structure of the GOF membrane, showing the GO nanosheets are cross-linked with EDA.


5

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 24

For high ion-selectivity between protons and vanadium ions, it is critical to control the effective pore size of the GOF membrane to dimensions capable of distinguishing between the hydrated diameters of vanadium ions and protons. This can be achieved by cross-linking the GO nanosheets with ethylenediamine (EDA) (Figure 1). The amine groups of the EDA react with the oxygen-containing functional groups of the GO; the nucleophilic attack of the amine to the epoxy and subsequent condensation reaction of the hydroxyl group results in C‒N covalent bonds.32-34 The C‒N covalent bonds stitch the GO nanosheets and form a framework structure.27, 29

The EDA provides the appropriate d spacing required for the VRFB application, as will be

demonstrated later. The GOF membrane was fabricated by integrating a thin GOF laminate on a hydrophilic porous polytetrafluoroethylene (PTFE) support (MILLIPORE; pore size of 0.45 µm) via vacuum filtration (see the “Experimental Section” for more details). Scanning electron microscopy (SEM) images revealed that the GOF film uniformly and completely covered the PTFE support (Figure 2a and Figure S1). The uniform thickness of the GOF film (~0.4 µm) was confirmed by a cross-sectional image of the GO membrane (Figure 2b). To confirm the cross-linking of the GOF membrane, the C 1s spectra from the X-ray photoelectron spectroscopy (XPS) of the GO and GOF membranes were compared, as shown in Figure 2c and 2d. After reacting with EDA, a peak at 285.8 eV for the C‒N bond newly appeared for the GOF membrane, while the peak at 286.5 eV for the C‒O group was reduced. This result clearly demonstrates that the epoxy and hydroxyl groups of the GO were substituted by chemical bonding between the EDA cross-linkers and GO sheets.


6

Page 7 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

The substitution of the oxygen functional groups by the C‒N bonds was further evidenced by Fourier transform-infrared spectroscopy (FTIR) spectra of the GO and GOF membranes, as shown in Figure S2. The spectrum of the GO membrane exhibits absorption peaks at 3188, 1731, 1373, 1225, and 1054 cm-1 which can be attributed to the stretching vibrations of O‒H in hydroxyl, C=O, carboxy C‒O, epoxy C‒O, and alkoxy C‒O bonds, respectively.35 After the cross-linking reaction, the peak intensities of the oxygen functional groups were notably decreased, and new absorption peaks at 1649 and 1558 cm-1 arose, which correspond to the stretching vibrations of C‒N and N‒H bonds,34, 36 confirming the connection of the EDA crosslinker and GO. The pore sizes of the dry and hydrated GOF membranes were measured by X-ray diffraction (XRD) technique. From the XRD peak originating from the regular spacing of the layered GO nanosheets, the values for d-spacing can be quantified, as shown in Figure 2e and 2f. In a dry state, the d-spacing was 8.4 Å and 8.9 Å for GO and GOF, respectively. The larger d-spacing of the GOF is attributed to the inclusion of the cross-linker between the GO nanosheets. After hydration, the d of the GO membrane increased to 14.5 Å because of the intercalation of two or three layers of water molecules between the GO nanosheets, as illustrated in the inset of Figure 2e.22, 27 In contrast, the GOF membrane exhibited only a slight increase in d, from 8.9 Å to 9.3 Å (Figure 2f). The large difference in the change of d upon hydration between the GO (6.1 Å) and GOF (0.4 Å) membranes indicates that cross-linking can prevent excessive water inclusion and resist the expansion of the interlayer spacing. The pore size of the GO membrane can be determined by substracting the thickness of a single graphene layer (3.4 Å) from the d-spacing; the pore sizes of GO and GOF membranes were determined to be 11.1 Å and 5.9 Å, respectively. The GO membrane cannot effectively sieve vanadium ions, since the hydrated diameter of


7

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 24

vanadium ions (> 6.0 Å, multivalent metal ions) is smaller than its pore size.37-38 By contrast, the pore size of GOF (5.9 Å) is smaller than the hydrated size of vanadium ions, but still larger than that of protons (< 2.5 Å).39-40 Therefore, due to the pore size exclusion, the GOF membrane can effectively block the tranport of vanadium ions but allow proton transport, which is highly advantageous for use in VRFB.


8

Page 9 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 2. Basic characterizations of the GOF membrane. SEM images of (a) the surface and (b) a cross-section of the GOF membrane. C 1s XPS spectra of (c) the GO membrane and (d) the GOF membrane. XRD patterns of the dry state and hydrated state: (e) the GO membrane and (f) the GOF membrane. The insets show illustrations of the GO nanosheets changing their interlayer spacing, d, in the dry and hydrated states, respectively, for the GO and GOF membranes.

To investigate the effect of crosslinking in selective ion transfer of vanadium species and proton, VO2+ ion permeability and area specific resistance (ASR) of GO and GOF membranes were measured as shown on Figure S3. The GOF membrane showed a much lower vanadium permeability than the GO membrane, demonstrating the blocking of vanadium ions by the modulated pore size with crosslinking. Furthermore, the ASR of the GOF membrane was only slightly larger (0.030 Ω cm2) than that of the GO membrane (0.024 Ω cm2) due to the pore size allowing proton transport. The stability of the GOF membrane in vanadium electrolytes was assessed by investigating the structural change of the GOF membrane upon immersion in the vanadium electrolytes. Figure S4 presents the XRD patterns for the GOF membranes after being immersed in V2+, V3+, VO2+, and VO2+ electrolytes for 48 h. For the VO2+ and VO2+ positive electrolytes, the d values were 9.0 Å and 9.1 Å, respectively, which are slightly smaller than that of the as-prepared GOF membrane (9.3 Å). This is because the electrostatic repulsion between the GO nanosheets is suppressed in the acidic conditions, due to the ionic screening effect of the protons.41-43 Nevertheless, the pore sizes of the GOF membrane after being soaked in the positive electrolyte (5.6 and 5.7 Å for VO2+ and VO2+ solutions) were still suitable for selective ion transfer in VRFB. However, after immersion in the negative electrolytes (V2+ and V3+ solutions), the XRD peaks were significantly


9

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 24

shifted to a higher 2 , indicating a decrease in d. The value for d was 3.8 Å for the V2+ electrolyte and 3.9 Å for the V3+ electrolyte. Such small spacings are characteristic of a reduced GO with high barrier characteristics.44 For further investigation, XPS measurements were conducted on the GOF membranes immersed in the various vandium electrolytes. As shown in the C 1s spectra (Figure S5), the preservation of the cross-linking was confirmed by the appearance of the peak at 285.8 eV from the C‒N bond, regardless of the kind of electrolytes, verifying the chemical stability of the C‒N bond in both positive and negative electrolytes. For the GOF membranes immsersed in the V2+ and V3+ electrolytes, however, the oxygen peaks (C‒ O, C=O, O‒C=O groups) from the GO sheet were smaller than those for the pristine, and the membranes immersed in the VO2+ and VO2+ electrolytes. These results show that the GO sheets are reduced by the reductive V2+ and V3+ ions. With the reduction of the GO, the interspacing was severly reduced due to the removal of oxygen functional groups on the GO surface and a stronger sp2 interaction, consequently resulting in the blocking of ion tranport. Because it is chemically reduced in the negative electrolytes, GOF membrane cannot be used alone as a VRFB membrane. However, the advantage of the GOF membrane can be exploited for VRFB by placing the GOF membrane on the positive side of the HC membrane, as a protective layer. Considering the stability of the GOF membrane with the positive electrolyte, and of the HC membrane with the negative electrolyte, a synergic GOF/HC membrane combination seems attractive. A SPAES membrane, which has a very high proton to vanadium ion selectivity but poor chemical stability,18 was selected as the HC membrane. Figure 3a shows a schematic of the GOF/SPAES membrane; the GOF layer supported by the porous PTFE support is placed on the positive side of the SPAES layer. Without additional procedure, the GOF membrane is simply superimposed on the SPAES membrane. The GOF layer can protect the SPAES membrane by


10

Page 11 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

sieving the oxidative VO2+ ions, and, at the same time, the SPAES membrane can shield the GOF membrane from the negative electrolytes. VO2+ permeability was examined by using a diffusion cell for the SPAES and GOF/SPAES membranes to confirm the vanadium ion sieving property of the GOF membrane. Nafion 115 membrane (thickness of 125 µm) was also compared to assess the applicability of the GOF/SPAES membrane for practical use. As shown in Figure 3b, the VO2+ concentration linearly increased with time for the Nafion 115, SPAES, and GOF/SPAES membranes. However, the SPAES and GOF/SPAES membranes showed much slower increases than Nafion 115, indicating a slower diffusion of VO2+ through the membranes. It is well known that the lower

vanadium

permeability of

the

SPAES

membrane

comes

from

its

smaller

hydrophobic/hydrophilic separation of rigid chain structure.8 VO2+ ion permeability was quantified from the slopes of the lines. The permeability was determined to be 1.33×10-3, 2.22×10-4, and 5.29×10-5 mol L-1 h-1 for the Nafion 115, SPAES, and GOF/SPAES membranes, respectively. The GOF/SPAES membrane exhibited 25 times lower vanadium permeability than the Nafion 115 membrane, and 4.2 times lower than the SPAES membrane. The significant decrease in vanadium ion permeability by combining the GOF membrane and the SPAES membrane demonstrates the excellent sieving of VO2+ by the GOF membrane. This result suggests that the GOF membrane can further reduce vanadium ion crossover, achieving higher coulombic efficiency (CE) and higher capacity retention, and protect the SPAES membrane in the GOF/SPAES membrane from the positive electrolyte for improved durability. ASR of the Nafion 115, SPAES, and GOF/SPAES membranes were measured using electrochemical impedance spectroscopy (EIS) and the results are compared in Figure 3c. The ASR of the GOF/SPAES membrane (0.125 Ω cm2) was 0.044 Ω cm2 larger than that of the


11

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 24

SPAES membrane (0.081 Ω cm2) due to the GOF and the porous PTFE support layers. The ASR from the GOF layer was 0.030 Ω cm2, according to the ASR value for the stack of the SPAES membrane and the PTFE support (0.095 Ω cm2). The small ASR of the GOF layer could be attributed to rapid proton conduction through the nano-capillary pathways between the GO nanosheets.22, 30-31 Considering the smaller ASR and lower vanadium ion permeability of the GOF/SPAES membrane compared with those of Nafion 115, the GOF/SPAES membrane was superior to Nafion 115 for use in VRFB.

Figure 3. Membrane characterizations of the GOF/SPAES membrane. (a) A schematic of the GOF/SPAES membrane. (b) The change in VO2+ ion concentration in the blank solution with


12

Page 13 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

time during the vanadium permeability measurement with the diffusion cell. (c) ASR values for the Nafion 115, SPAES, and GOF/SPAES membranes (the green dotted line represents the ASR of the SPAES+PTFE membrane).

Because of its high ion selectivity and facile proton conduction, the GOF/SPAES membrane can achieve excellent electrochemical performance in the VRFB. Furthermore, if the GOF membrane can effectively shield the SPAES membrane, the durability of the VRFB can be enhanced. The electrochemical performance of a VRFB cell with the GOF/SPAES membrane was investigated and compared with cells prepared with Nafion 115 and SPAES membranes. Figure 4a shows the results of a self-discharge test, which indicates the relative degree of vanadium crossover. The open circuit voltage (OCV) of a 50% charged VRFB cell was monitored in idle mode. The OCVs gradually decreased with time and sharply dropped at a certain time, indicating there was significant mixing of the positive and negative electrolytes. The SPAES membrane showed a much longer self-discharge duration time (185 h) than Nafion 115 (52 h) due to its lower vanadium permeability. As expected from the vanadium ion permeability results, the addition of the GOF membrane to the SPAES membrane further increased the self-discharge duration time to 315 h, which demonstrates that the superior vanadium ion sieving property of the GOF layer can affect VRFB performance. The performance of VRFB cells with Nafion 115, SPAES, and GOF/SPAES membranes were evaluated for five cycles with successively increasing current densities from 40 to 200 mA cm-2. The resulting coulombic efficiencies, voltage efficiencies (VEs), and energy efficiencies (EEs) are compared in Figure 4b, 4c, and 4d respectively. Regardless of the membranes, CE increased and VE decreased with increasing current density due to the decreased time for vanadium ion


13

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 24

crossover, and increased polarization, respectively. Compared with the SPAES membrane, the GOF/SPAES membrane exhibited higher CEs and lower VEs, resulting in similar EEs, results which are in accordance with the vanadium ion permeability and ASR results. It is notable that the GOF/SPAES and SPAES delivered much higher CEs and EEs than those of the Nafion 115 membrane over all the current densities investigated, which emphasizes the practical benefits of the SPAES and GOF/SPAES membranes.


14

Page 15 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Figure 4. Electrochemical performances of the VRFBs with Nafion 115, SPAES, and GOF/SPAES membranes: (a) self-discharge test; (b) CE, (c) VE, and (d) EE of the VRFB cells at various current densities from 40 to 200 mA cm-2. Cycling performances of the VRFBs with the


15

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 24

Nafion 115, SPAES, and GOF/SPAES membranes at a current density of 80 mA cm-2: (e) discharge capacity, and (f) CE and EE.

To ensure reliability in the VRFB, the membranes must demonstarte stable operation during cycling, as well as capacity retention and chemical stability over extended cycling. To determine whether the GOF membrane enhanced cycling stability, VRFB cells using different membranes were cycled at a current density of 80 mA cm-2. As shown in Figure 4e, the Naifon 115 membrane exhibited a rapid decay in capacity due to the high vanadium ion crossover, which is the most critical problem observed in Nafion-based conventional VRFBs. In contrast, the SPAES membrane showed much slower capacity decay during the initial 80 cycles, due to the lower vanadium permeability. However, the SPAES-based cell showed a sharp capacity drop after the 80th cycle, accompanying the abrupt decrease in CE and EE as presented in Figure 4f. This sudden failure was caused by the degradation of the SPAES membrane by VO2+ ions, as demonstrated in previous studies.9,

18-19

The GOF/SPAES-based cell, however, was able to

maintain stable operation for over 400 cycles (Figure 4e and 4f, and Figure S6; charge-discharge profiles), which corresponds to a more than five-fold durability enhancement. The improved durability with the GOF/SPAES membrane can mainly be attributed to the GOF membrane, not the PTFE support, since the VRFB with operated with a stack of SPAES membrane and PTFE support showed a decrease in efficiency after 109 cycles (Figure S7). These results clearly demonstrate that the chemical stability of the SPAES membrane was greatly improved by the additional GOF membrane. Its efficacy is better than that of the Nafion protection layer reported in our previous publication.18 Due to the high ion selectivity of the GOF membrane, the highly protective effect can be achieved without negating energy efficiency. Moreover, the VRFB


16

Page 17 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

assembled with the GOF/SPAES membrane achieved remarkably higher capacity retention (88% of initial capacity at 400th cycle) compared with the Nafion 115-based VRFB (13% of initial capacity at 200th cycle), which can be ascribed to the combined features of the SPAES and GOF membranes. It should also be noted that the GOF membrane was stable against the negative electrolyte in the GOF/SPAES configuration during cycling. Since the reduction of GOF by the negative electrode increases membrane resistance, the VE should have decreased in such event. However, the charging and discharge voltages of the GOF/SPAES membrane-based cell were stably maintained for over 400 cycles, as shown in Figure S6, confirming its stability against the negative electrolytes. The postmortem XPS analysis of the GOF membrane after long-term cycling further confirms its chemical stability (Figure S8a). In addition, there was no obvious change found in the postmortem SEM analysis of the GOF membrane after 180 cycles (Figure S8b). This suggests that the physical properties of the GOF membrane are sufficient for VRFB application. In summary, we successfully developed a highly ion-selective GOF membrane and combined it with a SPAES membrane to overcome the poor chemical stability of the SPAES membrane for use in VRFB. By cross-linking the GO nanosheets, a pore size with high selectivity between protons and vanadium ions was achieved, as well as high structural stability upon hydration. The crosslinked GOF membrane was placed as a protective layer between the SPAES membrane and positive electrolyte. The introduction of the GOF membrane reduced vanadium ion permeability by the pore size exclusion, while allowing fast proton conduction. A VRFB with the GOF/SPAES membrane showed much higher efficiency, and remarkably lower capacity decay rate than a Nafion 115-based VRFB. The VRFB with the GOF/SPAES membrane was able to


17

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 24

stably operate for over 400 cycles, in contrast to the sudden failure of a VRFB with a bare SPAES membrane after 80 cycles, demonstrating the advantage of the GOF membrane for extending the durability of HC membrane-based VRFBs.

ASSOCIATED CONTENT Supporting Information The following file is available free of charge. Detailed experimental methods for membrane preparation, characterization, and VRFB cell test. SEM images of the PTFE support, FTIR spectra of GOF membrane, XRD and C 1s XPS spectra after soaking in vanadium electrolytes, charge-discharge profiles of the GOF/SPAES membranebased VRFB, cycling performance of the VRFB with a stack comprised of SPAES membrane and PTFE support, SEM image of the GOF membrane after cycling (PDF)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Phone: 82-42-350-3931 *E-mail: [email protected]. Phone: 82-42-350-3916 Author Contributions §

S. K. and J. C. contributed equally to this work.

ACKNOWLEDGMENT


18

Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

This Research has been performed as a cooperation project of “Enhancing durability of redox flow batteries” and supported by the Korea Research Institute of Chemical Technology (KRICT). In addition, this work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20152010103210), and the Climate Change Research Hub of KAIST (Grant No. : N1117056). This work was supported by KAIST institute for the NanoCentury (KINC).

REFERENCES 1.

Yang, Z.; Zhang, J.; Kintner-Meyer, M. C.; Lu, X.; Choi, D.; Lemmon, J. P.; Liu, J.

Chem. Rev. 2011, 111, 3577-3613. 2.

Wang, W.; Luo, Q.; Li, B.; Wei, X.; Li, L.; Yang, Z. Adv. Funct. Mater. 2013, 23, 970-

986. 3.

Skyllas-Kazacos, M.; Chakrabarti, M.; Hajimolana, S.; Mjalli, F.; Saleem, M. J.

Electrochem. Soc. 2011, 158, R55-R79. 4.

Sun, C.; Chen, J.; Zhang, H.; Han, X.; Luo, Q. J. Power Sources 2010, 195, 890-897.

5.

Luo, Q.; Li, L.; Wang, W.; Nie, Z.; Wei, X.; Li, B.; Chen, B.; Yang, Z.; Sprenkle, V.

ChemSusChem 2013, 6, 268-274. 6.

Viswanathan, V.; Crawford, A.; Stephenson, D.; Kim, S.; Wang, W.; Li, B.; Coffey, G.;

Thomsen, E.; Graff, G.; Balducci, P. J. Power Sources 2014, 247, 1040-1051. 7.

Mai, Z.; Zhang, H.; Li, X.; Bi, C.; Dai, H. J. Power Sources 2011, 196, 482-487.


19

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

8.

Page 20 of 24

Xi, J.; Li, Z.; Yu, L.; Yin, B.; Wang, L.; Liu, L.; Qiu, X.; Chen, L. J. Power Sources

2015, 285, 195-204. 9.

Kim, S.; Tighe, T. B.; Schwenzer, B.; Yan, J.; Zhang, J.; Liu, J.; Yang, Z.; Hickner, M.

A. J. Appl. Electrochem. 2011, 41, 1201-1213. 10. Chen, D.; Hickner, M. A. Phys. Chem. Chem. Phys. 2013, 15, 11299-11305. 11. Yuan, Z.; Li, X.; Hu, J.; Xu, W.; Cao, J.; Zhang, H. Phys. Chem. Chem. Phys. 2014, 16, 19841-19847. 12. Chen, D.; Wang, S.; Xiao, M.; Meng, Y. Energy Environ. Sci. 2010, 3, 622-628. 13. Lee, J. Y.; Yu, D. M.; Kim, T.-H.; Yoon, S. J.; Hong, Y. T. J. Membr. Sci. 2015, 492, 209-219. 14. Yin, B.; Li, Z.; Dai, W.; Wang, L.; Yu, L.; Xi, J. J. Power Sources 2015, 285, 109-118. 15. Jo, S. G.; Kim, T.-H.; Yoon, S. J.; Oh, S.-G.; Cha, M. S.; Shin, H. Y.; Ahn, J. M.; Lee, J. Y.; Hong, Y. T. J. Membr. Sci. 2016, 510, 326-337. 16. Luo, Q.; Zhang, H.; Chen, J.; You, D.; Sun, C.; Zhang, Y. J. Membr. Sci. 2008, 325, 553558. 17. Jia, C.; Liu, J.; Yan, C. J. Power Sources 2012, 203, 190-194. 18. Kim, S.; Yuk, S.; Kim, H. G.; Choi, C.; Kim, R.; Lee, J. Y.; Hong, Y. T.; Kim, H.-T. J. Mater. Chem. A 2017, 5, 17279-17286. 19. Yu, L.; Xi, J. ACS Appl. Mater. Interfaces 2016, 8, 23425-23430.


20

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

20. Nair, R.; Wu, H.; Jayaram, P.; Grigorieva, I.; Geim, A. Science 2012, 335, 442-444. 21. Sun, P.; Zhu, M.; Wang, K.; Zhong, M.; Wei, J.; Wu, D.; Xu, Z.; Zhu, H. ACS Nano 2012, 7, 428-437. 22. Joshi, R.; Carbone, P.; Wang, F.-C.; Kravets, V. G.; Su, Y.; Grigorieva, I. V.; Wu, H.; Geim, A. K.; Nair, R. R. Science 2014, 343, 752-754. 23. Abraham, J.; Vasu, K. S.; Williams, C. D.; Gopinadhan, K.; Su, Y.; Cherian, C. T.; Dix, J.; Prestat, E.; Haigh, S. J.; Grigorieva, I. V. Nat. Nanotechnol. 2017, 12, 546-550. 24. Huang, J.-Q.; Zhuang, T.-Z.; Zhang, Q.; Peng, H.-J.; Chen, C.-M.; Wei, F. ACS Nano 2015, 9, 3002-3011. 25. Shaibani, M.; Akbari, A.; Sheath, P.; Easton, C. D.; Banerjee, P. C.; Konstas, K.; Fakhfouri, A.; Barghamadi, M.; Musameh, M. M.; Best, A. S. ACS Nano 2016, 10, 7768-7779. 26. Zhuang, T. Z.; Huang, J. Q.; Peng, H. J.; He, L. Y.; Cheng, X. B.; Chen, C. M.; Zhang, Q. Small 2016, 12, 381-389. 27. Hung, W.-S.; Tsou, C.-H.; De Guzman, M.; An, Q.-F.; Liu, Y.-L.; Zhang, Y.-M.; Hu, C.C.; Lee, K.-R.; Lai, J.-Y. Chem. Mater. 2014, 26, 2983-2990. 28. Jia, Z.; Wang, Y. J. Mater. Chem. A 2015, 3, 4405-4412. 29. Jia, Z.; Wang, Y.; Shi, W.; Wang, J. J. Membr. Sci. 2016, 520, 139-144. 30. Karim, M. R.; Hatakeyama, K.; Matsui, T.; Takehira, H.; Taniguchi, T.; Koinuma, M.; Matsumoto, Y.; Akutagawa, T.; Nakamura, T.; Noro, S.-i. J. Am. Chem. Soc. 2013, 135, 80978100.


21

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 24

31. Gao, W.; Wu, G.; Janicke, M. T.; Cullen, D. A.; Mukundan, R.; Baldwin, J. K.; Brosha, E. L.; Galande, C.; Ajayan, P. M.; More, K. L. Angew. Chem., Int. Ed. 2014, 53, 3588-3593. 32. Park, S.; Dikin, D. A.; Nguyen, S. T.; Ruoff, R. S. J. Phys. Chem. C 2009, 113, 1580115804. 33. Kim, N. H.; Kuila, T.; Lee, J. H. J. Mater. Chem. A 2013, 1, 1349-1358. 34. Wang, Z.; Dong, Y.; Li, H.; Zhao, Z.; Wu, H. B.; Hao, C.; Liu, S.; Qiu, J.; Lou, X. W. D. Nat. Commun. 2014, 5, 5002. 35. Yang, D.; Velamakanni, A.; Bozoklu, G.; Park, S.; Stoller, M.; Piner, R. D.; Stankovich, S.; Jung, I.; Field, D. A.; Ventrice Jr, C. A. Carbon 2009, 47, 145-152. 36. Pulikkathara, M. X.; Kuznetsov, O. V.; Khabashesku, V. N. Chem. Mater. 2008, 20, 2685-2695. 37. Yang, R.; Xu, Z.; Yang, S.; Michos, I.; Li, L.-F.; Angelopoulos, A. P.; Dong, J. J. Membr. Sci. 2014, 450, 12-17. 38. Yuan, Z.; Zhu, X.; Li, M.; Lu, W.; Li, X.; Zhang, H. Angew. Chem., Int. Ed. 2016, 55, 3058-3062. 39. Newton, M. D.; Ehrenson, S. J. Am. Chem. Soc. 1971, 93, 4971-4990. 40. Tuckerman, M.; Laasonen, K.; Sprik, M.; Parrinello, M. J. Chem. Phys. 1995, 103, 150161. 41. Huang, H.; Mao, Y.; Ying, Y.; Liu, Y.; Sun, L.; Peng, X. Chem. Commun. 2013, 49, 5963-5965.


22

Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

42. Klechikov, A.; Yu, J.; Thomas, D.; Sharifi, T.; Talyzin, A. V. Nanoscale 2015, 7, 1537415384. 43. Zheng, S.; Tu, Q.; Urban, J. J.; Li, S.; Mi, B. ACS Nano 2017, 11, 6440-6450. 44. Su, Y.; Kravets, V.; Wong, S.; Waters, J.; Geim, A.; Nair, R. Nat. Commun. 2014, 5, 4843.


23

Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 24

Table of Contents Graphic


24

Pore Size-Tuned Graphene Oxide Framework as ... - ACS Publications

Recommend Documents