Constructing Long-Range Transfer Pathways with Ordered AcidâBase

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Energy, Environmental, and Catalysis Applications

Constructing Long-Range Transfer Pathways with Ordered Acid-Base Pairs for Highly Enhanced Proton Conduction Yarong Liu, Wenjia Wu, Ping Li, Jianlong Lin, Zhihao Yang, and Jingtao Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b21081 • Publication Date (Web): 19 Feb 2019 Downloaded from http://pubs.acs.org on February 21, 2019

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ACS Applied Materials & Interfaces

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Constructing Long-Range Transfer Pathways with Ordered Acid-Base

2

Pairs for Highly Enhanced Proton Conduction

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Yarong Liua,1, Wenjia Wua,b,1, Ping Lia, Jianlong Lina, Zhihao Yanga, Jingtao Wang a,*

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a

8

S Supporting Information ●

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ABSTRACT: Acid-base pairs hold great superiority in creating proton defects and

10

facilitating proton transfer with less or no water. However, the existing acid-base

11

complexes failing in assembling into ordered acid-base pairs and thus cannot always take

12

full advantage of acid-base synergetic effect. Herein, polymer quantum dots (PQDs) with

13

inherent ordered acid-base pairs are utilized and anchored on dopamine coated graphene

14

oxide (DGO), and thus forming into long-range conducting pathways. The resultant

15

building blocks (nPGO) are integrated in sulfonated poly(ether ether ketone) matrix to

16

fabricate composite membrane. The constructed long-range transfer highways with ordered

17

acid-base pairs impart composite membrane significantly enhanced proton conduction

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ability. Under hydrated state, the composite membrane attains 91% increase over the

19

control membrane in conductivity and the single cell fuel based on the membrane achieves

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71% promotion in maximum power density. Under anhydrous condition, more striking

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augment in conduction is observed for composite membrane, reaching 7.14 mS cm−1,

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almost 10 times of the control membrane value (0.78 mS cm−1). Remarkably, such

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anhydrous proton conduction performance is even comparable to that of composite

24

membrane impregnated with ionic liquids, which is hard to realize with conventional fillers.

25

Collectively, these results endow composite membranes great potential for application in

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hydrogen-based fuel cell, sensor, and catalysis.

27 28

KEYWORDS: polymer quantum dot, inherent ordered acid-base pairs, graphene oxide, long-range transfer highways, composite membrane, proton conduction

School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001, P. R. China Department of Civil and Environmental Engineering, Center for the Environmental Implications of NanoTechnology (CEINT), Duke University, Durham, North Carolina 27708, USA 1 These authors made an equivalent contribution to this work. b

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ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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

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1. INTRODUCTION

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High proton conduction materials, especially ones that can work efficiently under elevated

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temperatures and low humidity conditions, are urgently desired in the hydrogen fuel cell

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and sensor areas.1 As the benchmark, Nafion membrane shows excellent proton conduction

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under fully hydrated condition,2,3 while under the low-humidity and high-temperature

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conditions, it should be not eligible because of the severe deterioration of proton

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conduction, rooting in the loss of water.4,5 Up to now, massive endeavors have been paid

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out for developing membranes which could be capable of working under above-mentioned

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conditions.6-15 A general approach is to impregnate the membrane with low-volatile proton

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solvents (e.g., N-heterocycle, phosphonic acid, and ionic liquid).6-12 This can alleviate the

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major problems associated with proton conduction, due to the presence of low-volatile

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proton hopping sites. However, these composite membranes always suffer from serious

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mechanical strength decline and proton solvent leaching, resulted from the plasticizing

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effect and water-soluble property of proton solvents.9,13-15

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A strategy of acid-base composites offers potential to address these problems by forming

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acid-base pairs, which generate proton defects and then enable a fast Grotthuss-type proton

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transfer.16-28 So far, the developed acid-base pairs are commonly divided into two

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categories. One is incorporating functionalized (acidic or basic) nanofillers into (basic or

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acidic) polymer matrix.16-18 Ueda et al. obtained a 88 % increase in anhydrous conductivity

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at 140 °C for the phosphoric acid-doped SPEEK membrane (from 4.0 to 7.5 mS cm−1) with

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the introduction of 3 wt.% polybenzimidazole (PBI)-grafted graphene oxide (GO).19 The

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other is blending basic polymers (e.g., PBI, chitosan (CS)) with acidic polymers (e.g., 2


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sulfonated polysulfone (PSf), sulfonated poly(ether ether ketone) (SPEEK)).20-24 Fu and

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co-workers blended SPEEK with benzimidazole-grafted polysulfone to prepare composite

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membrane, which gave an enhanced proton conductivity of 0.2 mS cm-1 under anhydrous

4

condition in contrast to plain SPEEK membrane (0.06 mS cm-1) at 120 oC.25 However, the

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conductivity enhancements of these membranes are limited, as the random distribution of

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acid-base sites diminish corresponding synergistic effect of acid-base pairs in creating

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proton defects. Furthermore, the formed acid-base pairs generally unable to construct

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long-range highways. For the former case, it necessitates boring pretreatment to avoid the

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precipitation of polyelectrolyte complex.26-28 While for the latter case, the inhibited chain

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motility generated by steric hindrance of fillers always makes the acid and base sites far

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away from each other. Accordingly, materials with inherent ordered acid-base pairs as well

12

as with potential to be engineered into long-range pathways hold great promise to conquer

13

these problems.

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Recently, the research on polymer quantum dots (PQDs) has been paid much

15

attention.29-31 They possess some intrinsic advantages for application as efficient proton

16

carriers, including abundant conducting groups and molecular size of 2-10 nm, both of

17

which are readily to be engineered. Importantly, the inherent ordered acid-base pairs with

18

short inter-distance make it an ideal candidate for anhydrous proton conduction (Figure S1).

19

In a previous work,32 we have incorporated PQDs into Nafion and observed increased

20

proton conduction ability. However, the PQDs in Nafion were also discretely distributed.

21

Thus we speculate that more significant conduction enhancement might be achieved if

22

PQDs can be sequentially assembled. 3



1

Herein, novel building blocks with inherent ordered acid-base pairs are designed and

2

prepared to create long-range proton transfer highways: anchoring PQDs on dopamine

3

coated GO (nPGO). Dopamine was introduced to increase the anchoring sites and strength,

4

thus facilitating sequential distribution of PQDs. The nPGOs were incorporated in SPEEK

5

matrix to prepare composite membrane. SPEEK was chosen due to the good film-forming

6

property, excellent thermal and chemical stabilities, acceptable proton conduction ability,

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and low cost. By comparing the nPGOs-filled membrane to references composed of DGO

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or PQDs, we demonstrate that the ordered acid-base pairs are assembled onto long-range

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transfer highways along

nPGO-SPEEK

interface, giving highly enhanced proton

10

conduction. And the conduction property is well controlled by PQD loading and acid-base

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pair amount on nPGO. The proton conductivity of composite membrane gives an obvious

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91% increase over the control membrane and the hydrogen fuel cell output power based on

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this membrane gains a 71% enhancement under hydrated condition. These results have

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surpassed most SPEEK-based composite membranes. Most significantly, these ordered

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pairs show an anhydrous conductivity of 7.14 mS cm-1 at 120 oC. This powerful proton

16

conduction ability is almost one-order of magnitude higher than that of plain SPEEK

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membrane, even comparable to that of ionic liquid-impregnated membranes. Such

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performances are difficult to attain by traditional fillers. Furthermore, this work gives new

19

ideas to design efficient proton conducting materials under hydrated or anhydrous

20

condition.

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2. EXPERIMENTAL SECTION

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2.1. Materials and Chemicals. Citric acid (CA, 99.5%), graphite powders (45 μm), and 4


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diethylenetriamine (DETA, 99%) were purchased from Sigma-Aldrich. Sulfuric acid

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(H2SO4, 98 wt.%), hydrogen peroxide (H2O2, 30 wt.%), N, N-dimethyl formamide (DMF),

3

and anhydrous ethyl alcohol were obtained from Bailingwei Technology Co., Ltd. Victrex®

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poly(ether ether ketone) (PEEK, grade 381G) was got from Nanjing Yuan9bang

5

Engineering Plastics Co., Ltd. Potassium permanganate (KMnO4) was acquired from

6

Kewei Chemistry Co., Ltd. Distilled water was utilized in the whole experiment.

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2.2. Synthesis of the Nanosheets and SPEEK. Graphite powders were oxidized to

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prepare GO based on the Hummers’ method.33 Dopamine coated GO (DGO) was also

9

synthetized according to the method in literature.34 Here, four kinds of nPGOs, where n (n

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= 1, 2, 3, 4) represented different PQD loading, were synthesized as following: 0.96 g citric

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acid (2.5 mol L-1) and 540 µL diethylenetriamine (2.5 mol L-1) were dissolved in DGO

12

aqueous solution (2.0 g) under ultrasonic treatment at ambient temperature for 5 min. Next,

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the mixture was put in a microwave-oven (750 W) to heat for 5 min, and then

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ultrasonically washed several times using 98% w/w ethanol, for removing residual

15

unreacted substance. Afterwards, the resultant products were dispersion in water, and

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3PGO

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kinds of nPGOs were prepared by adjusting DETA and CA concentration (0.1, 1.0, 2.5, and

18

5.0 mol L-1), as shown in Table S1. Besides, two graphene oxide quantum dots (GQDs)

19

with elevated carbonization degree (GmGO) were yielded by altering the solution to a

20

mixture of DGO aqueous solution (1.0 g L-1) and glycerol. The mass of DGO solution and

21

glycerol was 1.0 and 1.0 g, and 0.5 and 1.5 g, for G1GO and G2GO, respectively. PEEK

22

was sulfonated to obtain SPEEK with ~ 62% sulfonation degree.35

was obtained by freeze drying process for 48 h. Using the above method, other three

5



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2.3. Preparation of the Membranes. A certain amount of nPGO was dispersed in 8.0 g

2

DMF and treated with ultrasonication for 2 h at ambient temperature. Next, 0.7 g SPEEK

3

was immersed in the mixture. In order to get a homogeneous dispersion, the mixture was

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beat up thoroughly overnight at room temperature, and then cast onto flat glass plates in

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terms of the method in literature under the same conditions.34 The membranes were termed

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as SP-nPGO-X, and X (1%, 2%, 5%, and 10%) denoted the weight percentage of nPGO.

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Because 10 wt.% nPGO loading amount occurred agglomeration, 5 wt.% was chosen to

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better investigate the influence of filler category on membrane performances. Using the

9

above methods, the resultant composite membranes were produced by dissolving 0.035 g

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DGO, 0.035 g PQD, and 0.035 g GmGO into 3.5 g DMF, and named, respectively, as

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SP-DGO-5%, SP-PQD-5%, and SP-GmGO-5%. The SPEEK control membrane (SP) was

12

also fabricated with the same method. Notably, the average thicknesses of composite

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membranes were ranged from 41 to 74 μm (Table S2).

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2.4. Characterization of the Nanosheets and Membranes. The morphology of the

15

nanosheets were studied via atomic force microscopy (AFM) using Bruker Dimension

16

FastScanTM and transmission electron microscopy (TEM) on FEI model TECNAI G2-TEM

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(200 kV). The membranes were tested by wide X-ray diffractometry (WAXD) (from 5 to

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60o) and small-angle X-ray scattering (SAXS) (0.1-4o) through a Bruker D8 Advance ECO.

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Mechanical properties of the membranes were measured by manipulating the elongation

20

rate to 2.0 mm min-1 with Testometric 350AX. The membranes were broken by freeze

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fracture method and observed via cross-sectional scanning electron microscopy (SEM)

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with a JSM-7500F. Differential scanning calorimetry (DSC) was employed in 204 F1 6


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NETZSCH. The nanosheets, prior to testing, were pressed into tablets and then immersed

2

in water for a few minutes. Under nitrogen atmosphere, the hydrated state of nanosheets

3

were also measured by heated from -60 oC to 80 oC with the heating rate of 5 oC min-1.

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Besides, the weight fraction of bound water (ωb) was estimated by deducting the amount of

5

free water from the total water uptake (ωt). Under nitrogen atmosphere, the membranes

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were preheated from 30 to 120 oC with the heating rate of 10 oC min-1, followed by cooling

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down to 90 oC and then reheating up to 260 oC. An Escalab250Xi system was utilized to

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test X-ray photoelectron spectroscopy (XPS) (Thermo Fisher Scientific, Escalab 250Xi,

9

U.S). Under nitrogen atmosphere, thermogravimetric analysis (TGA), elevating the

10

temperature from 30 to 800 oC with the heating rate of 10 oC min-1, was performed by

11

TGA-50 SHIMADZU.

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2.5. Measurements of Water Uptake and Area Swelling. The area swelling and water

13

uptake of the membranes were tested at various temperatures (30, 40, 50, and 60 oC) in

14

accordance with the method in literature.36

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2.6. Ion Exchange Capacity (IEC), Proton Conductivity, and Fuel Cell Performance.

16

The IEC values of membranes were tested by back-titration method.23 The anhydrous

17

temperature-dependent proton conductivity of the pre-dried membranes (from 30 to 120 oC)

18

was tested by the same method and experimental instrumentation in our previously

19

published work.11,14,32,34 These completely dried membranes were also measured at 80 oC

20

under various humidifies and recorded data points for 90 min at each humidity step. The

21

membranes were immersed in water for 48 h before the test and measured at different

22

temperatures (from 30 to 90 oC) at 100% RH. 7



1

The membrane electrode assemblies (MEAs) were fabricated by SP, SP-DGO-5%,

2

SP-nPGO-5%, and SP-GmGO-5% on the basis of the method in literature.37 The

3

performances of single fuel cell based on membrane were measured in series of

4

temperatures (from 30 to 60 oC) under 100% RH in the light of the experimental

5

instrumentation under the identical system conditions.38 The stability was tested at 60 oC

6

and 100% RH, as the constant voltage loading was 0.6 V.

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3. RESULTS AND DISCUSSION

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3.1. Synthesis of the Nanosheets. Quantum dot (QD)-anchored nanosheets were

9

synthetized through a one-pot, microwave-assisted condensation of DETA and CA on

10

DGO surface (Scheme 1). Poly-dopamine layer was introduced to increase the anchoring

11

sites and strength by the abundant, homogeneous affinity sites, including –NH2 and –NH–

12

(Figure S2). Here, four kinds of polymer quantum dots anchored DGO (nPGO) with

13

different PQD loadings were prepared by regulating the precursor concentration. And two

14

types of graphene like quantum dots anchored DGO (GmGO), with similar physical

15

structures to 3PGO but reduced acid-base pairs, were also synthesized through elevating

16

the carbonization degree (Table S1). TEM images, Figure 1a-d, Figures S3, show that GO

17

of single layer possesses typical sheet structure with lateral dimension of above 2 µm.

18

AFM images, Figure 1e-i, Figures S4, reveal that the thickness of GO is 1.1 nm with a

19

smooth surface. After the self-polymerization, a uniform poly-dopamine layer is coated on

20

GO surface, which elevates sheet thickness to 1.5 nm. The layer structure of DGO is well

21

maintained, while it becomes a little dark due to the presence of poly-dopamine layer.39

22

This layer brings abundant hydrophilic groups (FTIR, Figure 2a and Figure S1), thus 8


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1

facilitating the adsorption of citric acid and diethylenetriamine and hence the formation of

2

PQDs/GQDs. This can be clearly observed in TEM and AFM images (Figure S5) that a

3

large amount of point-like attachments (PQDs) are distributed on DGO surface. PQDs

4

exhibit no lattice structure due to the presence of rich –NH2 and –CO2H.40 And these PQDs

5

allow nPGO generate photoluminescence effect under 365 nm UV (Figure S6). All the

6

anchored PQDs show uniform 0D structure with a size of 2-3 nm, and the size keeps

7

unchanged with the precursor concentration (0.1-5.0 mol L-1). As shown in Figure 1g-i,

8

elevating precursor concentration obviously increases the number of PQDs when the

9

concentration is below 5.0 mol L-1. Similarly, GmGO with the well-retained layer structure

10

possesses uniformly-distributed GQDs (Figure S3b and c). The size of anchored GQDs is

11

around 2.5 nm (Figure S4c). It should be noted that, the PQDs and GQDs remain firmly

12

anchored on the nanosheets although they have been fully washed by ultrasonic treatment.

9



1 2 3 4

Figure 1. TEM and AFM images of the nanosheets: (a and e) GO, (b and f) DGO, (c and g) 1PGO, (d and h) 3PGO (inset: height profile along the purple line); (i) the corresponding height profiles of AFM images.

5

FTIR results confirm the coating of poly-dopamine layer on DGO surface due to the

6

existence of characteristic peak at 1381 cm-1 for C-O-H (Figure 2a).41,42 By comparison,

7

nPGO

8

N-H at 1647 and 1554 cm-1, respectively.43 Meanwhile, the intensity of these two bands

9

elevates from 1PGO to 3PGO, suggesting the increased PQD loading. XRD, Figure 2b,

10

displays an average intersheet distance of GO of 0.86 nm with a diffraction peak value of

11

10.3°.44 The diffraction peak of DGO shifts to 8.9°compared to GO, which suggests an

12

increased intersheet distance of 0.99 nm. After modification with PQDs, the ordered

13

stacking of DGO is destroyed, and the characteristic peak at around 10.0° disappears.45

gives rise to two new peaks of C=O stretching vibration band and the bending of

10


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While a new amorphous band at 23° appears in the spectrum of nPGO, related to the

2

stacked structure of PQDs.32,40 In addition, the intensity of this band strengthens with the

3

increase of PQD loading on nanosheet, i.e., from 1PGO and 3PGO. TGA curves in Figure

4

2c show that the nanosheets undergo the water evaporation (30-150 oC), the deoxygenation

5

of oxygen containing groups (200-410 oC), and the decomposition of GO backbone

6

(420-800 oC) stages.46 Compared with GO, the presence of poly-dopamine layer and PQDs

7

postpones the starting degradation temperature of DGO and nPGO, resulting from their

8

protection for oxygen containing groups of GO (Figure S7a).13,47 Moreover, the

9

poly-dopamine layer obviously elevates the char yield of DGO at 800 oC. Compared with

10

DGO, nPGO produces lower char yield because of the polymer-like component of PQDs

11

(Figure 2c and Figure S7b). And as PQDs loading increases, the char yield of nPGO

12

gradually reduces. Based on char yield data, it shows that the loading of PQDs is relatively

13

high: up to 67 wt.% for 3PGO, which is possible to form inter-connected packing (Table

14

S1). While for 4PGO, the PQD loading decreases to 56.6 wt.%. This should be attributed to

15

the high precursor concentration and hence high solution viscosity, which may inhibit the

16

enrichment of precursor near DGO surface. For another, GmGO exhibits a close thermal

17

degradation process to nPGO. Under close QD loading, GmGO displays higher thermal

18

stability with larger char yield than nPGO. This is because of the high stability of GQDs as

19

compared to PQDs.

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C=O

DGO

1

100

a

10.3

-COOH

C-O-H

PGO

C=O amide

PGO 3

N-H

GO DGO 1PGO

8.9

b

3PGO

80

GO DGO 1PGO

70

3PGO

90

Weight (%)

C-O

Relative intensity / a.u.

O-H GO

Transmittance / a.u.

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 31

c

60 50

49.6% 42.9%

40

36.2%

30

1 2

4000

3500

2100 1400 Wave number (cm-1)

700

10

20

30

2θ / 

40

50

100

200

300

400

500

600

700

800

Temperature (C)

Figure 2. (a) FTIR spectra, (b) XRD patterns, and (c) TGA curves of as-prepared nanosheets.

3

3.2. Characterization of the Membranes. Afterwards, the nanosheets were integrated

4

in SPEEK matrix for fabricating proton exchange membranes. Cross-sectional SEM image

5

of SP control membrane shows uniform and smooth morphology without any cracks

6

(Figure 3a). GO makes the cross-section of SP-GO-5% become obviously crude with some

7

cracks (Figure S8).13 While SP-DGO-5% exhibits fewer wrinkles, and the polymer-filler

8

interfaces are dense (Figure 3b). This phenomenon is resulted from the strong electrostatic

9

attraction between DGO (–NH2/–NH–) and SPEEK (–SO3H), which improves interfacial

10

compatibility.34 For composite membranes with nPGO (Figure 3d and e), the cross-section

11

is also smooth and uniform, like that of SP-DGO-5%. Differently, the polymer-filler

12

interfaces of SP-nPGO-5% seem looser. These phenomena should be attributed to that the

13

inherent –NH2/–NH– would form intra-molecular interactions with –CO2H on nPGO,

14

reducing the electrostatic attraction with –SO3H of SPEEK when compared with DGO

15

(only –NH2/–NH–). This can be justified by FTIR results of composite membranes (Figure

16

S9), where the peak intensity of –SO3H for SP-nPGO-5% is stronger than that for

17

SP-DGO-5%. To further verify this speculation, G1GO and G2GO with fewer functional

18

groups (Figures S10 and S11) were synthesized through the carbonization of

19

O-/N-containing groups. The drastically reduced loading of O-/N-containing groups for 12


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1

GmGO weakens its interaction with SPEEK matrix (Figure S12). Therefore, the interfacial

2

compatibility becomes worse (Figure S13), even similar to that of SP-GO-5%. In addition,

3

it is interesting to find that, the polymer-filler interface of SP-nPGO-5% is more tortuous

4

when compared with SP-DGO-5%, inferring the presence of PQDs along DGO surface.

5

This meanwhile brings obvious photoluminescence effect under 365 nm UV (SP-3PGO-5%,

6

Figure 3c and f).

7 8 9

Figure 3. Cross-sectional SEM images of (a) SP, (b) SP-DGO-5%, (d) SP-1PGO-5%, and (e) SP-3PGO-5%; photographs of (c) SP-DGO-5% and (f) SP-3PGO-5% under 365 nm UV.

10

WAXD results, Figure 4a, Figures S14a and b, reveal that all SPEEK-based membranes

11

display broad bands (2θ = 8-21°) because of the semicrystalline nature of the membranes.

12

The crystallinity is evaluated by the diffraction band in form of full width at half maximum

13

(FWHM) (Table 1).48 SP obtains a FWHM value of 6.24º. By comparison, incorporating

14

DGO, 1PGO, and 3PGO makes the FWHM of composite membranes increased to 7.33º,

15

7.28º, and 7.02º, respectively, indicating reduction in crystallinity.49 Crystallinity reduction

16

should be ascribed to that, the nanosheets disturb the self-assembly of SPEEK chains 13



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1

through mutual interactions. Therefore, the FWHM of SP-3PGO-5% is smaller than that of

2

SP-1PGO-5%, as it has weaker interaction with SPEEK matrix. Similarly, the FWHM of

3

SP-GmGO-5% is much smaller (Figure S14b). These speculations can be directly testified

4

by DSC as depicted in Figure 4b. The relaxation process of structural reorganization of

5

membranes results in the appearance of endothermic bands (from 179 to 214 °C).50 The

6

transition temperature (Td) of SP is 179.8 °C. Composite membranes attain elevated Td

7

values, because the interferences generated by nanosheets restrain chain mobility.51 Similar

8

to SEM and WAXD results, the Td values of the membranes decrease in order of

9

SP-DGO-5% > SP-1PGO-5% > SP-3PGO-5% > SP, in accordance with strength of

10

interfacial interactions. The nanophase separation structure of the membranes is reflected

11

by SAXS patterns (Figure 4c and Figures S14c and d). SP attains a q value of 0.21 nm-1,52

12

while DGO incorporation shifts this ionomer peak to an increased value, reaching 0.30

13

nm-1, indicating narrower ionic clusters. Compared with SP-DGO-5%,

14

composite membranes display smaller peak values, and the values for SP-1PGO-5% and

15

SP-3PGO-5% are 0.28 and 0.25 nm-1, respectively. In addition, the value for SP-GmGO-5%

16

is further decreased (Figure S14d). These phenomena should also be resulted from the

17

weakened interface interactions, resulting in larger ionic clusters relative to DGO-filled

18

composite membrane.

14


nPGO-filled

Page 15 of 31

184.6oC SP-3PGO-5%

Heat flow (a.u.)

Relative intensity (a.u.)

a SP SP-3PGO-5% SP-1PGO-5%

b

202.9oC SP-1PGO-5%

o

213.9 C SP-DGO-5%

179.8oC SP

SP-DGO-5% 10

20

30

40

50

2θ (degree)

60

140

160

180

200

Temperature (oC)

220

240

50

c

SP SP-DGO-5% SP-1PGO-5%

40

SP

q=0.21 nm

SP-3PGO-5%

q=0.25 nm

SP-1PGO-5%

q=0.28 nm

SP-DGO-5%

q=0.30 nm

d

SP-3PGO-5%

Stress (MPa)

Relative intensity (a.u.)

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


30

20

10

0

0.2

0.4

1

0.6

0.8 q (nm-1)

1.0

1.2

1.4

0

15

50

Strain()

55

2 3

Figure 4. (a) WAXD patterns, (b) DSC curves, (c) SAXS patterns, and (d) stress-strain curves of SPEEK control and composite membranes.

4

Table 1. The FWHM, relative FWHM, tensile strength, and elongation at break of the membranes. Tensile strength

Elongation at

[MPa]

break [%]

1

36.0

53.9

7.33±0.05

1.18

46.3

49.7

SP-1PGO-5%

7.28±0.05

1.17

31.7

17.4

SP-3PGO-5%

7.02±0.05

1.13

22.1

14.5

Membrane

FWHM(°)

Relative FWHM

SP

6.24±0.05

SP-DGO-5%

5

The mechanical properties of as-prepared membranes are exhibited in Figure 4d and

6

Figures S15a and b. The stress-strain curve of SP control membrane implies acceptable

7

mechanical properties, in which the elongation at break and tensile strength are,

8

respectively, 53.9% and 36.0 MPa (Table 1). By comparison, hybridizing GO into

9

membrane significantly reduces the mechanical properties (Figure S15a), leading the

10

elongation at break and tensile strength to 3.7% and 17.6 MPa, respectively. Compared 15



1

with SP-GO-5%, the interface attractions between nPGO and SPEEK matrix endow

2

SP-nPGO-5% with elevated tensile strength, and SP-3PGO-5% attains an elongation at

3

break of 14.5% and a tensile strength of 22.1 MPa. SP-GmGO-5% displays similar

4

mechanical properties to SP-nPGO-5% (Figure S15b). The elongation at break and tensile

5

strength of SP-DGO-5% reach to 49.7% and 46.3 MPa, respectively, because of the much

6

stronger interface attractions. Notly, TGA results imply that all membranes obtain

7

acceptable thermal stability (Figure S15c and d).

8

Water molecules can facilitate the proton transfer via vehicle and Grotthuss mechanism

9

due to the medium of proton conduction and the construction of hydrogen-bond networks.

10

SP gains the area swelling and water uptake of, respectively, 17.6% and 22.3% at 30 oC

11

(Table 2). Compared with SP, SP-GO-5% attains elevated area swelling and water uptake,

12

respectively, achieving 19.9% and 22.4%. (Figures S16 and Table S2). This should be

13

resulted from the additional space for water storage at polymer-nanosheet interfacial

14

domains.53,54 Upon modification with PQDs, the nanosheets generate electrostatic

15

attractions with SPEEK, making the interfacial domains hard to swell. The area swelling

16

and water uptake of SP-3PGO-5% are reduced to 17.7% and 20.7%, respectively.

17

Simultaneously, the area swelling and area swelling of composite membrane decrease with

18

the enhancement of interfacial attractions (Figures S16a and b). For SP-GmGO-5%, despite

19

the weak interfacial attractions, the relatively hydrophobic nature of GmGO makes

20

composite membrane exhibit lower area swelling and water uptake. In addition, the area

21

swelling and water uptake of the membranes all elevate with testing temperature (Figures

22

S16c and d), and composite membranes exhibit better structural stability than the control 16


Page 16 of 31

Page 17 of 31 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

1


membrane.

2

3

Table 2. Water uptake, area swelling, and IEC of the membranes.

a

Membrane

Water uptakea (%)

Area swellinga (%)

IEC (mmol g-1)

SP

22.3

17.6

1.76 ±0.02

SP-DGO-5%

13.3

11.2

1.62 ±0.02

SP-1PGO-5%

13.6

12.8

1.74 ±0.02

SP-3PGO-5%

20.7

17.7

1.93 ±0.02

Measurement was at 30 oC.

4

3.3. IEC and Proton Conductivity of the Membranes. Table 2 reveals that the IEC

5

value of SP is 1.76 mmol g-1. After inserting DGO into membrane, the IEC value decreases

6

to 1.62 mmol g-1 because of the appearance of acid-base pairs between DGO and SPEEK.14

7

Compared with SP-DGO-5%, SP-nPGO-5% achieves higher IEC value. For instance,

8

SP-1PGO-5%, SP-2PGO-5%, SP-3PGO-5%, and SP-4PGO-5% attain the IEC values of,

9

respectively, 1.74, 1.75, 1.93, and 1.87 mmol g-1 (Table S2). Such findings may be ascribed

10

to the intra-molecular interactions on nPGO, and thus allowing more –SO3H on SPEEK to

11

expose.

12

The investigation of proton conduction properties of the membranes are exhibited in

13

Figure 5 and Figures S17. At 30 oC and 100% RH, SP obtains the conductivity of 11.6 mS

14

cm-1 (Figure 5a). While the proton conductivity of SP-DGO-5% gains an elevated value of

15

18.4 mS cm-1. Given the reduced ionic cluster size, IEC, and water uptake, one reason for

16

the conductivity enhancement should be derived from the formed acid-base pairs along

17

polymer-nanosheet interface. Such presumption can be further testified by the increased

18

proton conductivity of SP-nPGO-5%, which possesses inherent ordered acid-base pairs in

19

proton transfer highways (Figure 5b and Figure S17a). Different from the random 17



1

acid-base pairs in SP-DGO-5%, the inherent acid-base pairs on PQDs are highly ordered

2

(Scheme 1, in order of -acid-base-acid-base-). Besides, these PQDs offer additional

3

hydrogen-bond donors and increase strong water bonding sites in SPEEK matrix, both of

4

which can jointly construct abundant water-mediated hydrogen-bonded transfer networks,

5

accelerating protons transfer through Grotthuss mechanism.32 Accordingly, SP-1PGO-5%

6

obtains a significantly enhanced conductivity of 23.1 mS cm-1. Increasing the number of

7

ordered acid-base pairs endows composite membrane with further elevated proton

8

conduction, and SP-3PGO-5% with highest PQD loading achieves a conductivity of 35.0

9

mS cm-1. In addition, SP-GmGO-5% displays lower proton conductivity than that of

10

SP-nPGO-5% due to the reduced O-/N-containing groups (i.e., acid-base pairs) (Figure

11

S17b). Another reason for the conduction augment of SP-DGO-5% as compared to SP

12

should be originated from the constructed long-range transfer highways along 2D sheet

13

interfaces. To verify this speculation, PQDs were prepared and introduced into SPEEK

14

matrix to obtain composite membrane. Despite the larger number of ordered acid-base

15

pairs (compared to nPGO), SP-PQD-5% displays a lower proton conduction ability of 21.1

16

mS cm-1 due to the dis-continuous packing of PQDs in membrane (Figure S17b).

17

Meanwhile, the conductivities of membranes all increase with the temperature (Figure 5b,

18

Figures S17a and b). The maximum hydrated conductivity of SP-3PGO-5% (76.5 mS cm-1)

19

at 90 oC is 1.9 times that of SP (11.6 mS cm-1). Besides, the extent of performance augment

20

in this study is much larger than that of most existing SPEEK composite membranes filled

21

by imidized-GO, microcapsules, N-decorated carbon nanotubes, or alkaline g-C3N4,

22

etc,55-57 highlighting the superiority of ordered acid-base pairs in boosting proton 18


Page 18 of 31

Page 19 of 31

conduction.

30

100% RH, 30C 0% RH, 30°C

2.8 80

2.4 2.0

25

1.6 20

1.2 15

0.8

10

0.4

5 0

SP

DG

5% O-

-

SP

S

O PG P- 1

-5%

-5%

S

SP-1PGO-5%

15.9

SP-3PGO-5%

14.6

4

21.8 SP SP-DGO-5% 16.6

2

0 20

40

60

80

Temperature (oC)

60

SP-3PGO-5%

50 40 30 20 10 30

100

40

50

60

70

80

90

Temperature (oC)

c

Ea (kJ mol-1)

b

SP SP-DGO-5% SP-1PGO-5%

70

O PG P- 3

8

6

0.0

Proton conductivity (mS cm-1)

35

a



40


1


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


120

40

RH=40%

RH=20%

RH=60%

d

30

20

10

SP-1PGO-5% SP-3PGO-5%

SP SP-DGO-5%

0 0

30

60

Time (min)

90

2 3 4 5 6

Figure 5. (a) Proton conductivity of membrane at 100% RH (30 oC) and 0% RH (30 oC), (b) temperature-dependent proton conductivity of membrane at 100% RH, (c) temperature-dependent proton conductivity of membrane at 0% RH, and (d) RH-dependent proton conductivity of membrane for 90 min at 80 oC in dry state.

7

The proton conductivity is displayed in Figure 5c and Figure S17c under anhydrous

8

condition. The conductivity of SP is 0.15 and 0.78 mS cm-1 at 30 and 120 oC, respectively.

9

SP-DGO-5% exhibits enhanced anhydrous proton conduction property. The conductivity

10

reaches, respectively, 0.35 and 1.24 mS cm-1 at 30 and 120 oC. This should be due to the

11

constructed long-range transfer highways as well as the formed acid-base pairs along it,

12

which reduce transfer energy barrier. This can be testified by the decreased Ea values of

13

SP-DGO-5% (16.6 kJ mol-1) compared to SP (21.8 kJ mol-1) (Figure 5c and Figure S17d).

14

By comparison, the introduction of nPGO with inherent ordered acid-base pairs along

15

nPGO-SPEEK

interface gives SP-nPGO-5% highly enhanced proton conductivity. The 19



1

anhydrous conductivity of SP-1PGO-5% elevates to 0.75 and 2.49 mS cm-1 at 30 and 120

2

o

3

resulted from that, protons can fast transport among the adjacent donors (–CO2H) and

4

acceptors (H2N–/–HN–) on PQDs via accelerated protonation/de-protonation process with

5

reduced enthalpy change.58,59 Moreover, the anhydrous proton conduction can be further

6

enhanced by increasing the loading of acid-base pairs. In such way, the enrichment of PQD

7

on nPGO surface possibly forms relatively continuous proton transfer highways. Thus,

8

SP-3PGO-5% gains the maximum anhydrous conductivity of 7.14 mS cm-1, almost

9

one-order of magnitude of that of SP at 120 oC. And this performance is even comparable

10

C, respectively, with a reduced Ea value of 15.9 kJ mol-1. This enhancement should be

to that of polymeric membranes impregnated with ionic liquids.8,11,14

11

In addition, RH-dependent proton conductivity of as-prepared membranes was tested

12

(Figure 5d). In contrast with SP and SP-DGO-5%, composite membranes with nPGO

13

display stronger moisture absorbing ability, especially for SP-3PQD-5%. It reaches

14

equilibrium within 15 min at each RH and then keeps a constant conductivity. While for

15

SP and SP-DGO-5%, they need more than 30 min. This strong moisture absorbing ability

16

should be derived from the hydrophilic groups on PQDs. In order to verify this speculation,

17

the powders of GO, DGO, and nPGO were pressed into tablet and then used to absorb

18

water molecules, followed by measuring their state (free or bound water) on DSC (Figure

19

S18 and Table S3).60,61 The water uptakes of GO and DGO tablets are 8.5% and 8.2%,

20

respectively, in which the ratio of bound water are 84.7% and 90.2%. By Comparison,

21

nPGO

22

14.2% and 17.6%, respectively, with the bound water ratio up to 96.5% and 98.9%.

exhibits stronger water absorbing ability: the water uptakes of 1PGO and 3PGO are

20


Page 20 of 31

Page 21 of 31 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


1

Composite membranes with other three contents of 3PGO were also prepared and tested.

2

The conductivity varies with

3

performances due to the highest PQD loading (Figure S19).

3PGO

content, and SP-3PGO-5% presents the best

4 5

Scheme 1. Schematic of the preparation and proton conduction mechanism of composite membrane.

6

3.4. Single Cell Performance. The hydrogen fuel cell performances of the membranes

7

are exhibited in Figure 6 and Figures S20. The open circuit voltages of all membranes

8

suggest respectable gas barrier ability, which are above 0.9 V. SP obtains the maximum

9

power density and current density of, respectively, 106.9 mW cm-2 and 369.6 mA cm-2 at

10

50 oC and 100% RH. Compared with SP, the power density and current density of

11

SP-DGO-5% gain increased values, respectively, reaching 120.7 mW cm-2 and 422.6 mA

12

cm-2. Such performance should be resulted from the enhanced gas barrier ability and

13

proton conduction of SP-DGO-5%. As for SP-nPGO-5%, the maximum power density and

14

current density are further highly elevated, whose trends are in accordance with the proton

15

conductivity (Figure S20a and b). Particularly, SP-3PGO-5% achieves the maximum power

16

density and current density of, respectively, 183.1 mW cm-2 and 580.7 mA cm-2, which are

17

1.6 times and 1.7 times higher than that of SP. From a comparison with other 21



Page 22 of 31

1

SPEEK-based composite membranes (Table S4), it is observed that nPGO are more

2

efficient to elevate the cell output power based on membrane than most of the fillers.

3

Simultaneously, the maximum power density and current density of SP-3PGO-5% increase

4

with the operating temperatures (30-60 °C) (Figure S20c). Furthermore, the stability of the

5

operation of the MEA was also detected based on SP-3PGO-5% for more than 60 h at a

6

constant voltage of 0.6 V. Notly, the single cell based on membrane does not exhibit any

7

degradation for 60 h (Figure 6b), demonstrating an excellent operation stability.

8 9 10

Figure 6. (a) Single cell performances of the membrane under 50 oC and 100% RH, and (b) the durability of SP-3PGO-5% in single cell operated at 60 oC and 0.6 V with humidified (100% RH) H2/O2.

11

4. CONCLUSIONS

12

In summary, we have proved, in polymer electrolyte membrane,

nPGO

is capable of

13

constructing efficient long-range proton transfer highways. For this novel nanosheets,

14

PQDs are uniformly and firmly anchored on DGO, providing inherent ordered acid-base

15

pairs along sheet surface. By homogeneously dispersing in composite membrane, nPGOs

16

highly

17

low-energy-barrier transfer highways. Under hydrated condition, composite membrane

18

achieves an obvious 91% promotion over SP in proton conduction and a 71% improvement

19

in maximum power density. The performance is superior to most of the existing SPEEK

strengthen

the

proton

conduction

ability

22


of

membrane

by

forming

Page 23 of 31 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


1

membranes. More significantly, in the case of anhydrous proton conductivity, these ordered

2

acid-base pairs provide much stronger enhancement. The conductivity of SP-3PGO-5%

3

(0.78 mS cm-1) is almost one-order of magnitude higher than SP (7.14 mS cm-1) at 120 oC.

4

Such performance is comparable to that of ionic liquid-impregnated membranes, and also

5

much higher than that of composite membranes hybridized by GO, DGO, and PQDs, as

6

they fail to create ordered and long-range acid-base paired pathways. The conduction

7

property of composite membrane shows obvious dependence on the loading of acid-base

8

pairs. Accordingly, the distinctive design of these conducting materials makes great

9

potential for practical application of hydrogen-based fuel cell, sensor, and catalysis.

10

■ ASSOCIATED CONTENT

11

S Supporting Information ●

12

TEM images of 4PGO and GmGO. AFM topography images of 1PGO, 4PGO, and G2GO.

13

C 1s spectra of PQD, 3PGO, and G2GO. TGA curves of DGO, PQD, nPGO, and GmGO.

14

DSC curves of state of water in nanosheets. SEM images of SP-GO-5% and SP-G2GO-5%

15

through the cross-sectional scan. FTIR spectra, WAXD patterns, and SAXS patterns of the

16

membranes. Proton conductivity, area swelling, and water uptake of the membranes with

17

different filler contents. Anhydrous and hydrous conductivities of the membranes.

18

■ AUTHOR INFORMATION

19

Corresponding Author

20

*E-mail: [email protected]. Tel: 86-371-63887135. Fax: 86-371-63887135.

21

Notes

22

The authors declare no competing financial interest. 23



1

■ ACKNOWLEDGMENTS

2

This work is highly acknowledged by the Program for Science & Technology Innovation

3

Talents in Universities of Henan Province (18HASTIT002) and National Natural Science

4

Foundation of China (21576244). Global Scholar Program for Doctoral Students of

5

Zhengzhou University and Fok Ying Tung Education Foundation (161065) are also

6

supported.

7

■ REFERENCES

8

(1) Sadakiyo, M.; Okawa, H.; Shigematsu, A.; Ohba, M.; Yamada, T.; Kitagawa, H. Promotion of

9

Low-Humidity Proton Conduction by Controlling Hydrophilicity in Layered Metal-Organic

10

Frameworks. J. Am. Chem. Soc. 2012, 134, 5472–5475.

11

(2) Moghaddam, S.; Pengwang, E.; Jiang, Y. B.; Garcia, A. R.; Burnett, D. J.; Brinker, C. J.; Masel, R.

12

I.; Shannon, M. A. An Inorganic-Organic Proton Exchange Membrane for Fuel Cells with a Controlled

13

Nanoscale Pore Structure. Nat. Nanotechnol. 2010, 5, 230–236.

14

(3) Patel, H. A.; Mansor, N.; Gadipelli, S.; Brett, D. J. L.; Guo, Z. Superacidity in Nafion/MOF Hybrid

15

Membranes Retains Water at Low Humidity to Enhance Proton Conduction for Fuel Cells. ACS Appl.

16

Mater. Interfaces 2016, 8, 30687–30691.

17

(4) Karim, M. R.; Hatakeyama, K.; Matsui, T.; Takehira, H.; Taniguchi, T.; Koinuma, M.; Matsumoto,

18

Y.; Akutagawa, T.; Nakamura, T.; Noro, S. I.; Yamada, T.; Kitagawa H.; Hayami S. Graphene Oxide

19

Nanosheet with High Proton Conductivity. J. Am. Chem. Soc. 2013, 135, 8097–8100.

20

(5) Bukola, S.; Liang, Y.; Korzeniewski, C.; Harris, J.; Creager, S. Selective Proton/Deuteron Transport

21

through Nafion|Graphene|Nafion Sandwich Structures at High Current Density. J. Am. Chem. Soc. 2018,

22

140, 1743–1752.

23 24

(6) Verma, A.; Scott, K. Development of High-Temperature PEMFC Based on Heteropolyacids and Polybenzimidazole. J. Solid State Electrochem. 2010, 14, 213–219.

25

(7) Kim, S.; Joarder, B.; Hurd, J. A.; Zhang, J.; Dawson, K. W.; Gelfand, B. S.; Wong, N. E.; Shimizu,

26

G. K. H. Achieving Superprotonic Conduction in Metal-Organic Frameworks through Iterative Design

27

Advances. J. Am. Chem. Soc. 2018, 140, 1077–1082. 24


Page 24 of 31

Page 25 of 31 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


1

(8) Mondal, A. N.; Tripathi, B. P.; Shahi, V.K. Highly Stable Aprotic Ionic-Liquid Doped Anhydrous

2

Proton-Conducting Polymer Electrolyte Membrane for High-Temperature Applications. J. Mater. Chem.

3

2011, 21, 4117–4124.

4

(9) Bu, F.; Zhang, Y.; Hong, L.; Zhao, W.; Li, D.; Li, J.; Na, H.; Zhao, C. 1,2,4-Triazole Functionalized

5

Poly(arylene ether ketone) for High Temperature Proton Exchange Membrane with Enhanced Oxidative

6

Stability. J. Memb. Sci. 2018, 545, 167–175.

7

(10) Campagne, B.; David, G.; Améduri, B.; Jones, D. J.; Rozière, J.; Roche, I. Novel Blend

8

Membranes of Partially Fluorinated Copolymers Bearing Azole Functions with Sulfonated PEEK for

9

PEMFC Operating at Low Relative Humidity: Influence of the Nature of the N-Heterocycle.

10

Macromolecules 2013, 46, 3046–3057.

11

(11) Zhang, H.; Wu, W.; Wang, J.; Zhang, T.; Shi, B.; Liu, J.; Cao, S. Enhanced Anhydrous Proton

12

Conductivity of Polymer Electrolyte Membrane Enabled by Facile Ionic Liquid-Based Hoping

13

Pathways. J. Memb. Sci. 2015, 476, 136–147.

14 15

(12) Jang, S.; Kim, S. Y.; Jung, H. Y.; Park, M. J. Phosphonated Polymers with Fine-Tuned Ion Clustering Behavior: Toward Efficient Proton Conductors. Macromolecules 2018, 51, 1120–1128.

16

(13) Kowsari, E.; Zare, A.; Ansari, V. Phosphoric Acid-Doped Ionic Liquid-Functionalized Graphene

17

Oxide/Sulfonated Polyimide Composites as Proton Exchange Membrane. Int. J. Hydrogen Energy 2015,

18

40, 13964–13978.

19

(14) Wu, W.; Li, Y.; Chen, P.; Liu, J.; Wang, J.; Zhang, H. Constructing Ionic Liquid-Filled Proton

20

Transfer Channels within Nanocomposite Membrane by Using Functionalized Graphene Oxide. ACS

21

Appl. Mater. Interfaces 2016, 8, 588–599.

22

(15) Singh, B.; Duong, N. M. H.; Henkensmeier, D.; Jang, J. H.; Kim, H. J.; Han, J.; Nam, S. W.

23

Influence of Different Side-Groups and Cross-Links on Phosphoric Acid Doped Radel-Based

24

Polysulfone Membranes for High Temperature Polymer Electrolyte Fuel Cells. Electrochim. Acta 2017,

25

224, 306–313.

26 27

(16) Rambabu, G.; Bhat, S. D. Amino Acid Functionalized Graphene Oxide Based Nanocomposite Membrane Electrolytes for Direct Methanol Fuel Cells. J. Memb. Sci. 2018, 551, 1–11.

28

(17) Beydaghi, H.; Javanbakht, M.; Kowsari, E. Synthesis and Characterization of Poly(vinyl

29

alcohol)/Sulfonated Graphene Oxide Nanocomposite Membranes for Use in Proton Exchange 25



1

Membrane Fuel Cells (PEMFCs). Ind. Eng. Chem. Res. 2014, 53, 16621–16632.

2

(18) Anahidzade, N.; Abdolmaleki, A.; Dinari, M.; Firouz, K. Metal-Organic Framework Anchored

3

Sulfonated Poly(ether sulfone) as a High Temperature Proton Exchange Membrane for Fuel Cells. J.

4

Memb. Sci. 2018, 565, 281–292.

5

(19) Shirdast, A.; Sharif, A.; Abdollahi, M. Effect of the Incorporation of Sulfonated

6

Chitosan/Sulfonated Graphene Oxide on the Proton Conductivity of Chitosan Membranes. J. Power

7

Sources 2016, 306, 541–551.

8

(20) Jheng, L. C.; Huang, C. Y.; Hsu, S. L. C. Sulfonated MWNT and Imidazole Functionalized

9

MWNT/Polybenzimidazole Composite Membranes for High-Temperature Proton Exchange Membrane

10

Fuel Cells. Int. J. Hydrogen Energy 2013, 38, 1524–1534.

11

(21) Qiu, X.; Ueda, M.; Hu, H.; Sui, Y.; Zhang, X.; Wang, L. Poly(2,5-benzimidazole)-Grafted

12

Graphene Oxide as an Effective Proton Conductor for Construction of Nanocomposite Proton Exchange

13

Membrane. ACS Appl. Mater. Interfaces 2017, 9, 33049–33058.

14 15

(22) Mack, F.; Aniol, K.; Ellwein, C.; Kerres, J.; Zeis, R. Novel Phosphoric Acid-Doped PBI-Blends as Membranes for High-Temperature PEM Fuel Cells. J. Mater. Chem. A 2015, 3, 10864–10874.

16

(23) Muthumeenal, A.; Neelakandan, S.; Kanagaraj, P.; Nagendran, A. Synthesis and Properties of

17

Novel Proton Exchange Membranes Based on Sulfonated Polyethersulfone and N-Phthaloyl Chitosan

18

Blends for DMFC Applications. Renew. Energy 2016, 86, 922–929.

19

(24) Ahmadian-Alam, L.; Mahdavi, H. Preparation and Characterization of PVDF-Based Blend

20

Membranes as Polymer Electrolyte Membranes in Fuel Cells: Study of Factor Affecting the Proton

21

Conductivity Behavior. Polym. Adv. Technol. 2018, 29, 2287–2299.

22

(25) Fu, Y.; Manthiram, A.; Guiver, M. D. Acid-Base Blend Membranes Based on

23

2-Amino-Benzimidazole and Sulfonated Poly(ether ether ketone) for Direct Methanol Fuel Cells.

24

Electrochem. commun. 2007, 9, 905–910.

25 26

(26) Smitha, B.; Sridhar, S.; Khan, A. A. Polyelectrolyte Complexes of Chitosan and Poly(acrylic acid) as Proton Exchange Membranes for Fuel Cells. Macromolecules 2004, 37, 2233–2239.

27

(27) Li, Z.; Jiang, Z.; Tian, H.; Wang, S.; Zhang, B.; Cao, Y. Preparing Alkaline Anion Exchange

28

Membrane with Enhanced Hydroxide Conductivity via Blending Imidazolium-Functionalized and

29

Sulfonated Poly(ether ether ketone). J. Power Sources 2015, 288, 384–392. 26


Page 26 of 31

Page 27 of 31 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


1

(28) Lin, Y.-F.; Hsiao, Y.-H.; Yen, C.-Y.; Chiang, C.-L.; Lee, C.-H.; Huang, C.-C.; Ma, C.-C. M.

2

Sulfonated Poly(propylene oxide) Oligomers/Nafion® Acid-Base Blend Membranes for DMFC. J.

3

Power Sources 2007, 172, 570–577.

4

(29) Zhu, S.; Meng, Q.; Wang, L.; Zhang, J.; Song, Y.; Jin, H.; Zhang, K.; Sun, H.; Wang, H.; Yang, B.

5

Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging. Angew.

6

Chem. Int. Ed. 2013, 52, 3953–3957.

7

(30) Kong, B.; Zhu, A.; Ding, C.; Zhao, X.; Li, B.; Tian, Y. Carbon Dot-Based Inorganic-Organic

8

Nanosystem for Two-Photon Imaging and Biosensing of pH Variation in Living Cells and Tissues. Adv.

9

Mater. 2012, 24, 5844–5848.

10 11 12 13 14 15

(31) Gupta, V.; Chaudhary, N.; Srivastava, R.; Sharma, G. D.; Bhardwaj, R.; Chand, S. Luminscent Graphene Quantum Dots for Organic Photovoltaic Devices. J. Am. Chem. Soc. 2011, 133, 9960–9963. (32) Wu, W.; Li, Y.; Liu, J.; Wang, J.; He, Y.; Davey, K.; Qiao, S. Z. Molecular-Level Hybridization of Nafion with Quantum Dots for Highly Enhanced Proton Conduction. Adv. Mater. 2018, 30, 1707516. (33) Marcano, D. C.; Kosynkin, D. V; Berlin, J. M.; Sinitskii, A.; Sun, Z.; Slesarev, A.; Alemany, L. B.; Lu, W.; Tour, J. M. Improved Synthesis of Graphene Oxide. ACS Nano 2010, 4, 4806–4814.

16

(34) He, Y.; Wang, J.; Zhang, H.; Zhang, T.; Zhang, B.; Cao, S.; Liu, J. Polydopamine-Modified

17

Graphene Oxide Nanocomposite Membrane for Proton Exchange Membrane Fuel Cell under

18

Anhydrous Conditions. J. Mater. Chem. A 2014, 2, 9548–9558.

19

(35) Ru, C.; Li, Z.; Zhao, C.; Duan, Y.; Zhuang, Z.; Bu, F.; Na, H. Enhanced Proton Conductivity of

20

Sulfonated Hybrid Poly(arylene ether ketone) Membranes by Incorporating an Amino-Sulfo

21

Bifunctionalized Metal-Organic Framework for Direct Methanol Fuel Cells. ACS Appl. Mater.

22

Interfaces 2018, 10, 7963–7973.

23 24

(36) Li, P.; Wu, W.; Liu, J.; Shi, B.; Du, Y.; Li, Y.; Wang, J. Investigating the Nanostructures and Proton Transfer Properties of Nafion-GO Hybrid Membranes. J. Memb. Sci. 2018, 555, 327–336.

25

(37) Wu, W.; Wang, J.; Liu, J.; Chen, P.; Zhang, H. Intercalating Ionic Liquid in Graphene Oxide to

26

Create Efficient and Stable Anhydrous Proton Transfer Highways for Polymer Electrolyte Membrane.

27

Int. J. Hydrogen Energy 2017, 42, 11400–11410.

28

(38) Zhao, L.; Li, Y.; Zhang, H.; Wu, W.; Liu, J.; Wang, J. Constructing Proton-Conductive Highways

29

within an Ionomer Membrane by Embedding Sulfonated Polymer Brush Modified Graphene Oxide. J. 27



1 2 3

Power Sources 2015, 286, 445–457. (39) Xu, L. Q.; Yang, W. J.; Neoh, K. G.; Kang, E. T.; Fu, G. D. Dopamine-Induced Reduction and Functionalization of Graphene Oxide Nanosheets. Macromolecules 2010, 43, 8336–8339.

4

(40) Yuan, Z.; Wu, X.; Jiang, Y.; Li, Y.; Huang, J.; Hao, L.; Zhang, J.; Wang, J. Carbon

5

Dots-Incorporated Composite Membrane towards Enhanced Organic Solvent Nanofiltration

6

Performance. J. Memb. Sci. 2018, 549, 1–11.

7

(41) Kaminska, I.; Das, M. R.; Coffinier, Y.; Niedziolka-Jonsson, J.; Sobczak, J.; Woisel, P.; Lyskawa,

8

J.; Opallo, M.; Boukherroub, R.; Szunerits, S. Reduction and Functionalization of Graphene Oxide

9

Sheets Using Biomimetic Dopamine Derivatives in One Step. ACS Appl. Mater. Interfaces 2012, 4,

10

1016–1020.

11

(42) Hwang, S. H.; Kang, D.; Ruoff, R. S.; Shin, H. S.; Park, Y. Bin. Poly(vinyl alcohol) Reinforced

12

and Toughened with Poly(dopamine)-Treated Graphene Oxide, and Its Use for Humidity Sensing. ACS

13

Nano 2014, 8, 6739–6747.

14

(43) Yang, L.; Kong, J.; Yee, W. A.; Liu, W.; Phua, S. L.; Toh, C. L.; Huang, S.; Lu, X. Highly

15

Conductive Graphene by Low-Temperature Thermal Reduction and In Situ Preparation of Conductive

16

Polymer Nanocomposites. Nanoscale 2012, 4, 4968–4971.

17

(44) Pandey, R. P.; Thakur, A. K.; Shahi, V. K. Sulfonated Polyimide/Acid-Functionalized Graphene

18

Oxide Composite Polymer Electrolyte Membranes with Improved Proton Conductivity and

19

Water-Retention Properties. ACS Appl. Mater. Interfaces 2014, 6, 16993–17002.

20 21

(45) Fang, M.; Wang, K.; Lu, H.; Yang, Y.; Nutt, S. Single-Layer Graphene Nanosheets with Controlled Grafting of Polymer Chains. J. Mater. Chem. 2010, 20, 1982–1992.

22

(46) Wang, J.; Zhao, L.; Wei, D.; Wu, W.; Zhang, J.; Cheng, X. Effects of Intercalated Molecules in

23

Graphene Oxide on the Interlayer Channels for Anhydrous Proton Conduction. Ind. Eng. Chem. Res.

24

2016, 55, 11931–11942.

25 26

(47) Tang, H.; Ehlert, G. J.; Lin, Y.; Sodano, H. A. Highly Efficient Synthesis of Graphene Nanocomposites. Nano Lett. 2012, 12, 84–90.

27

(48) Yang, J. M.; Wang, S. A. Preparation of Graphene-Based Poly(vinyl alcohol)/Chitosan

28

Nanocomposites Membrane for Alkaline Solid Electrolytes Membrane. J. Memb. Sci. 2015, 477, 49–57.

29

(49) Jiang, R.; Kunz, H. R.; Fenton, J. M. Composite Silica/Nafion® Membranes Prepared by 28


Page 28 of 31

Page 29 of 31 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


1

Tetraethylorthosilicate Sol-Gel Reaction and Solution Casting for Direct Methanol Fuel Cells. J. Memb.

2

Sci. 2006, 272, 116–124.

3

(50) Dong, X.-Y.; Wang, J.-H.; Liu, S.-S.; Han, Z.; Tang, Q.-J; Li, F.-F.; Zang, S.-Q. Synergy between

4

Isomorphous Acid and Basic MOFs for Anhydrous Proton Conduction of Low-Cost Hybrid Membranes

5

at High Temperature. ACS Appl. Mater. Interfaces 2018, 10, 38209–38216.

6

(51) Yin, Y.; Wang, H.; Cao, L.; Li, Z.; Li, Z.; Gang, M.; Wang, C.; Wu, H.; Jiang, Z.; Zhang, P.

7

Sulfonated Poly(ether ether ketone)-Based Hybrid Membranes Containing Graphene Oxide with

8

Acid-Base Pairs for Direct Methanol Fuel Cells. Electrochim. Acta 2016, 203, 178–188.

9 10

(52) Eisenberg, A. Clustering of Ions in Organic Polymers. A Theoretical Approach. Macromolecules 1970, 3, 147–154.

11

(53) Liu, Q.; Shi, J.; Sun, J.; Wang, T.; Zeng, L.; Jiang, G. Graphene and Graphene Oxide Sheets

12

Supported on Silica as Versatile and High-Performance Adsorbents for Solid-Phase Extraction. Angew.

13

Chem. Int. Ed. 2011, 50, 5913–5917.

14 15

(54) Compton, O. C.; Nguyen, S. T. Graphene Oxide, Highly Reduced Graphene Oxide, and Graphene: Versatile Building Blocks for Carbon-Based Materials. Small 2010, 6, 711–723.

16

(55) Shukla, G.; Shahi, V. K. Sulfonated Poly(ether ether ketone)/Imidized Graphene Oxide Composite

17

Cation Exchange Membrane with Improved Conductivity and Stability for Electrodialytic Water

18

Desalination. Desalination 2018, https://doi.org/10.1016/j.desal.2018.03.018.

19

(56) Gong, C.; Zheng, X.; Liu, H.; Wang, G.; Cheng, F.; Zheng, G.; Wen, S.; Law, W.-C.; Tsui, C.-P.;

20

Tang, C.-Y. A New Strategy for Designing High-Performance Sulfonated Poly(ether ether ketone)

21

Polymer Electrolyte Membranes Using Inorganic Proton Conductor-Functionalized Carbon Nanotubes.

22

J. Power Sources 2016, 325, 453–464.

23

(57) Dong, C.; Wang, Q.; Cong, C.; Meng, X.; Zhou, Q. Influence of Alkaline 2D Carbon Nitride

24

Nanosheets as Fillers for Anchoring HPW and Improving Conductivity of SPEEK Nanocomposite

25

Membranes. Int. J. Hydrogen Energy 2017, 42, 10317–10328.

26 27

(58) Li, Y.; Wang, S.; He, G.; Wu, H.; Jiang, Z. Facilitated Transport of Small Molecules and Ions for Energy-Efficient Membranes. Chem. Soc. Rev. 2015, 44, 103–118.

28

(59) Wang, J.; He, Y.; Zhao, L.; Li, Y.; Cao, S.; Zhang, B.; Zhang, H. Enhanced Proton Conductivities

29

of Nanofibrous Composite Membranes Enabled by Acid-Base Pairs under Hydrated and Anhydrous 29



1

Conditions. J. Memb. Sci. 2015, 482, 1–12.

2

(60) Choi, B. G.; Hong, J.; Park, Y. C.; Jung, D. H.; Hong, W. H.; Hammond, P. T.; Park, H. Innovative

3

Polymer Nanocomposite Electrolytes: Nanoscale Manipulation of Ion Channels by Functionalized

4

Graphenes. ACS Nano 2011, 5, 5167–5174.

5 6

(61) Tamura, T.; Kawakami, H. Membranes for Fuel Cell Electrolytes. Nano Lett. 2010, 10, 1324– 1328.

30


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Constructing Long-Range Transfer Pathways with Ordered AcidâBase

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