Ion-Transport Design for High-PerformanceNa+‑Based ElectrochromicsRan Li,†,# Kerui Li,†,# Gang Wang,*,‡ Lei Li,∥ Qiangqiang Zhang,† Jinhui Yan,⊥ Yao Chen,¶

Qinghong Zhang,§ Chengyi Hou,† Yaogang Li,§ and Hongzhi Wang*,†

†State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering,§Engineering Research Center of Advanced Glasses Manufacturing Technology, Ministry of Education, Donghua University, Shanghai201620, People’s Republic of China‡School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States∥State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China⊥Department of Civil and Environmental Engineering, University of Illinois, Urbana−Champaign, Illinois 61801, United States¶Key Laboratory of Green Chemistry and Technology (Ministry of Education), College of Chemistry, Sichuan University,Chengdu 610064, People’s Republic of China

*S Supporting Information

ABSTRACT: Sodium ion (Na+)-based electrochemical systems have been exten-sively investigated in batteries and supercapacitors and also can be qualitycandidates for electrochromic (EC) devices. However, poor diffusion kineticsand severe EC performance degradation occur during the intercalation/deintercalation processes because the ionic radii of Na+ are larger than those ofconventional intercalation ions. Here, through intentional design of ion-transportchannels in metal−organic frameworks (MOFs), Na+ serves as an efficientintercalation ion for incorporation into a nanostructured electrode with a highdiffusion coefficient of approximately 10−8 cm2 s−1. As a result, the well-designed MOF-based EC device demonstrates desirable Na+ EC performance,including fast switching speed, multicolor switching, and high stability. A smart“quick response code” display is fabricated using a mask-free laser writingmethod for application in the “Internet of Things”. In addition, the concept ofion transport pathway design can be widely adopted for fabricating high-performance ion intercalation materials anddevices for consumer electronics.

KEYWORDS: Na+ electrochromic device, efficient transport channel, metal−organic frameworks, multicolor display,smart quick response code

Sodium ion (Na+)-based electrochemical systems havebeen extensively investigated in batteries and supercapac-itors thanks to their low cost, moderate operating condi-

tions, and higher safety compared with traditional lithium ion(Li+)-based systems.1−4 Electrochromic (EC) devices, having astructure and operating principle similar to that of batteries andsupercapacitors, exhibit reflective optical phenomena and wideapplications ranging from smart windows and e-paper to wear-able camouflage and multicolor displays.5−10 The operation ofEC devices involves Faradaic reaction processes by means ofintercalation/deintercalation or doping/dedoping of ionswithin the EC electrode.11−13 Typically, monovalent H+- andLi+-based electrolytes are used in EC devices. However, acidicH+-based electrolytes have a strong tendency to corrode thesurface of electrodes and show a very narrow electrochemicalwindow because of their low hydrogen evolution potential.Li+-based electrolytes suffer from high cost and safety issues.14−16

Therefore, it is important to explore a new generation of cation-based electrolyte systems for EC devices.Inspired by research on Na+ energy storage devices, Na+-based

electrolytes have been attempted in EC devices. For example,Dini et al. observed an optical change of approximately 40%at 650 nm with Na+ intercalation into amorphous WO3 andformation of NaxWO3 compounds during the EC process.17

Panchal and co-workers compared the electrochromic proper-ties of H+, Na+, and K+ intercalated with WO3 and demon-strated the thermally crystalline WO3 thin film with a colorationefficiency (CE) of approximately 14.9 cm2 C−1 at 650 nm forNa+.18 However, these Na+-based EC electrodes still suffer frompoor performance compared with H+- and Li+-based devices,

Received: February 5, 2018Accepted: March 29, 2018Published: March 29, 2018

Artic

lewww.acsnano.orgCite This: ACS Nano 2018, 12, 3759−3768

© 2018 American Chemical Society 3759 DOI: 10.1021/acsnano.8b00974ACS Nano 2018, 12, 3759−3768

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which results from the slow diffusion kinetics of Na+ with thelarger ionic radius during the redox reaction process.19 There-fore, it is of great significance to develop new EC electrodematerials for efficient Na+ intercalation/deintercalation.Metal−organic frameworks (MOFs), constructed from metal-

based nodes and organic linkers, are crystal materials with highsurface areas, nanostructured pores, and tunable chemical com-position and structure. MOFs show a broad range of appli-cations, including in gas storage/separation, catalysis, andsensors.20−23 Attributed to their uniform and engineered channeldimensions, MOF-based electrodes can realize the desired masstransfer of various ions in multiple dimensions.24,25 Dinca’s groupfirst reported using naphthalene-diimide-based MOFs as anelectrochromic material with tetra-n-butylammonium hexa-fluorophosphate (TBAPF6) as electrolyte, and MOFs wereconsidered to be potential candidates and studied in TBA+-based electrolytes systems.26−29 Rougie et al. recently fabricateda reflective electrochromic device associating HKUST-1 andZn-MOF-74 films via a Li+-based gel electrolyte membrane.30

However, although these works demonstrate MOFs have elec-trochromic behaviors, these MOFs do not show advantages andcan be replaced when compared with other typical EC materialssuch as transition metal oxides or polymers in TBA+- andLi+-based electrolyte systems. The significance and value of MOFsin the EC field have not been regarded, and optical propertiesbetween cation species and channel sizes are not clear yet.In this contribution, MOFs were utilized as intercalation elec-

trodes to realize an efficient Na+-based EC device exhibitingrapid multicolor switching and high contrast and stability.The ion-transport channel design concept was clearly demon-strated by the intentional introduction of two kinds of 1,4,5,8-naphthalenediimide (NDI)-based MOF films with two channelsizes (radii of approximately 10 and 33 Å, respectively). Thedesired MOF EC electrode (radius of approximately 33 Å)

exhibited the fastest color diversity, from transparent to redand then to dark blue with high coloration efficiencies up to260 cm2 C−1 at 720 nm, electrochemical stability over 500 cycles,and high optical contrast (ΔT ≈ 73%) in the Na+-based elec-trolyte, which were higher than reported Na+-based EC mate-rials and other EC MOFs in traditional TBA+- and Li+-basedelectrolytes and also comparable with other cation intercalationEC systems. Additionally, a multicolor EC device with displaypixels was fabricated to demonstrate potential applications inconsumer electronics, accompanied by low cost and safety.A demonstration of a “quick response code” (QRC) smartdisplay was fabricated by mask-free laser writing for applicationin the “Internet of Things” (IOT).

RESULTS AND DISCUSSIONTwo MOFs with different crystal structures were intentionallyprepared to explore the influence of the pore structure on iondiffusion and the priority of large channels in ion transport,as well as to achieve satisfactory EC performance. Here, asone kind of common n-type semiconductor in organic elec-tronics,31−37 NDIs with photophysical properties were intro-duced as the functional redox groups in MOFs.38−40 Then,two MOFs, [Ni2(BINDI)(DMF)4]·2DMF (Ni-BINDI) and[Ni2(CHNDI)(H2O)2]·4H2O (Ni-CHNDI), were synthesizedto investigate their application for Na+-based EC devices. Moredetails about the synthesis, structure, and pore size distributionare provided in Schemes S1−S3, Table S1, and Figures S1−S5in the Supporting Information.As shown in Figure 1a−d and Figure S1 in the Supporting

Information, two MOF films were deposited on fluorine-dopedtin oxide (FTO) glass by a solvothermal method and composedof uniformly distributed acicular nanorods with a similar thicknessof approximately 500 nm and diameters ranging from 50 to70 nm. The similar micromorphology is conducive to avoiding

Figure 1. Microstructural analysis of the MOF materials. SEM images (top) and corresponding sectional TEM images (bottom) of (a, c)Ni-BINDI and (b, d) Ni-CHNDI films; (e) simulated and experimental XRD patterns of Ni-BINDI and Ni-CHNDI films; simulated structuresof crystalline (f) Ni-BINDI and (g) Ni-CHNDI; (h) N2 adsorption isotherm curves for Ni-BINDI and NI-CHNDI powders measured at 77 K.

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the influence of micromorphology on ionic diffusion during thefollowing comparisons, which is consistent with the followingelectrochemical results. Although the X-ray diffraction (XRD)patterns of Ni-BINDI and Ni-CHNDI thin films matched nicelywith the respective simulated XRD patterns (Figure 1e), thediffraction peaks of Ni-BINDI were obviously different fromthose of Ni-CHNDI, indicating that they had different crystal struc-tures.29,41 In the structure of the Ni-BINDI lattice (Figure 1f andScheme S2 in the Supporting Information), the material crys-tallizes in the I41/a space group with 2-fold interpenetratedequivalent nets constructed of Ni(II) ions and conjugatedπ-deficient NDI rings, which results in the formation of square-shaped channels with dimensions of ca. 10 Å. For Ni-CHNDI,one-dimensional hexagonal channels with diameters of ca. 33 Åwere constructed using a five-coordinated Ni(II) ion as thecommon vertex and six helical Ni−O−C rods of composition[Ni2O2](CO2)2 as the sides (Figure 1g and Scheme S3 in theSupporting Information).42

The channel size and specific surface areas of Ni-CHNDIand Ni-BINDI were investigated by N2 uptake isotherm exper-iments (Figure 1h). Ni-BINDI shows a typical type I isothermcorresponding to microporous materials.43,44 Fitting of the N2adsorption isotherm to the Dubinin−Astakhov sorption showsa pore size distribution of approximately 10 Å (Figure S2,Supporting Information), which is in good agreement with thecrystal structure data above (10 Å). By applying the Langmuirand Dubinin−Radushkevich equations, the specific surface areawas calculated to be 556 m2 g−1.45 The Ni-CHNDI displayed atypical type IV isotherm with high N2 uptake. The pore sizedistribution was calculated to be approximately 33 Å (Figure S3,Supporting Information), in agreement with the reported values.29

Through fitting the N2 adsorption isotherm to the BET equa-tion, the specific surface area was calculated to be 2077 m2 g−1.Based on the isotherm information, Ni-CHNDI has wider channelsand a larger pore volume.To further examine the superiority of the large hexagonal

channels in ion-solid diffusion, electrochemical impedance spec-troscopy (EIS) and cyclic voltammetry (CV) for the two MOFswere measured in 0.1 M NaClO4, TBAClO4, LiClO4, andAl(ClO4)3 in propylene carbonate (PC) electrolytes, respec-tively. As expected, the EIS spectra of the two MOFs in variouselectrolytes are quite different (Figure 2a and Figure S6 in theSupporting Information).46−48 The Nyquist plot is composedof three regions: (1) a line at low frequency related to the capac-itive behavior; (2) a sloping (ca. 45°) linear region at high tomedium frequency presenting diffusion resistance; and (3) asemicircle at high frequency characterized the charge-transferresistance. As shown in Figure 2a and Figure S7 in the SupportingInformation, an almost vertical line at low frequency of Ni-CHNDIin NaClO4 solution demonstrates the good capacitive behaviorfor Na+.49 Herein, the Nyquist plots were well fitted with an equiv-alent Randles circuit model inset in Figure 4a using the followingequation:

δ ω′ = + + + +− −Z R R Z C(CPE ( ) )S CT W1 1

w L (1)

where a solution resistance (RS), a charge-transfer resistance(RCT), related constant phase elements (CPE), a Warburgimpedance (ZW), and low-frequency mass capacitance (CL) wereemployed.50 Among them, RCT represents the charge-transferresistance at the electrode/electrolyte interface. As listed inTable S2 in the Supporting Information, the RCT values ofthe Ni-BINDI measured in NaClO4, TBAClO4, LiClO4, and

Figure 2. Electrochemical properties and ion-diffusion schematic. (a) Nyquist plots and corresponding simulation results (fitting lines) ofNi-CHNDI films measured in 0.1 M Na+-, Li+-, TBA+-, and Al3+-based electrolytes; (b) cyclic voltammetry curves of the Ni-CHNDI filmmeasured in 0.1 M NaClO4/PC solution at scan rates of 10, 25, 50, 75, 100, 125, and 150 mV s−1 (inset: dependence of anodic and cathodiccurrents on the square root of scan rates); (c) diffusion coefficients of Ni-BINDI and Ni-CHNDI for different ions calculated via EIS and CVmeasurements; (d) schematics of ion diffusion in Ni-BINDI and Ni-CHNDI channels.

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Al(ClO4)3 electrolytes were 48, 63, 91, and 303 Ω, respectively,while those for Ni-CHNDI were 43, 70, 121, and 282Ω,respectively. Therefore, in the same electrolyte, the differencesin RCT between Ni-BINDI and Ni-CHNDI are small, indicatingthat the two MOF films possess similar charge-transfer imped-ances because of the nearly identical micromorphology of free-standing nanorods. For both Ni-BINDI and Ni-CHNDI,the relationship among the RCT values of the four electrolytesis Na+ < TBA+ < Li+ < Al3+, and the different RCT values ofthe four electrolytes indicate that Na+ transfers most quickly tothe MOF electrode surface from solution during the electroninjection.51

In addition to RCT, the apparent ion diffusion coefficient(Dapp,W), which represents the kinetics of ion insertion/deinsertionin the electrode material, can be calculated from the Warburgslope of the short, straight-line section in the Warburg regionderived from Fick’s law according to eqs 2 and 3:52

δ ω= −Z A/W w1/2

(2)

=A E X D(d /d )/SFC(2 )W1/2

(3)

where A is the differences of the real and imaginary compo-nents of the impedance, ω is the angular frequency, δw repre-sents the slope of ZW against ω−1/2, and dE/dX is the derivativeof the electrode potential with respect to the intercalationisotherm; S, F, and C are the surface area, Faraday constant, andmolar concentrations of ions, respectively. Notably, as shown inFigure 2c, the Dapp,W values for Ni-BINDI in NaClO4,TBAClO4, LiClO4, and Al(ClO4)3 were calculated to be 7.54 ×10−9, 6.12 × 10−9, 2.67 × 10−9, and 1.86 × 10−10 cm2 s−1,respectively, which were much lower than those of Ni-CHNDI(3.21 × 10−8, 1.03 × 10−8, 9.67 × 10−9, and 1.21 × 10−9 cm2 s−1,respectively). For the same ion electrolyte, the huge differencebetween the ion diffusion coefficients of the two MOFs can beattributed to faster ion transportation in the larger hexagonalchannels of the Ni-CHNDI (33 Å vs 10 Å) crystal structure.To further investigate the results described above and explain

the ion solid diffusion mechanism in the large hexagonal channels,cyclic voltammetry for the MOF films was conducted and com-pared in four electrolytes. As shown in Figure 2b and Figure S10in the Supporting Information, both Ni-BINDI and Ni-CHNDIfilms displayed two pairs of redox peaks, consistent with reported[NDI]/[NDI]− and [NDI]−/[NDI]2− redox couples (Scheme S4,Supporting Information).37 The reduction peak (C1) correspond-ing to [NDI] to [NDI]− and oxidation peak (A2) correspondingto [NDI]2− to [NDI]− are relatively small in the NaClO4/PCelectrolyte; these may be caused by the second electron transferof NDI cores of MOFs being easier than the first one duringboth the oxidation and reduction processes in the PC-basedelectrolyte.53,54 As shown in the inset of Figure 2b, all the oxi-dation and reduction peak currents were proportional to thesquare root of the scan rates, indicating that the charge/dischargeprogress was controlled by diffusion and limited by cation inter-calation (Figure 2b).55 Thus, the apparent ion diffusion coef-ficients (Dapp,CV) in MOF films for Na+, TBA+, Li+, and Al3+

ions can be also calculated using the Randles−Sevcik equation:56

= × × × × × ×i n D C S v2.687 10p5 3/2

CV1/2

01/2

(4)

where C0 is the concentration of active ions in the electrolytesolution, v is the potential sweep rate, ip is the peak currentdensity, S is the surface area, and n is the number of electronsinvolved in the reaction. As listed in Table S3 in the Supporting

Information, the Dapp,CV of the Ni-CHNDI thin film with fourions (approximately 10−8 cm2 s−1 for Na+, TBA+, and Li+ and10−9 cm2 s−1 for Al3+) are an order of magnitude larger thanthose of Ni-BINDI (approximately 10−9 cm2 s−1 for Na+, TBA+,and Li+ and 10−10 cm2 s−1 for Al3+), which agrees with the resultsfrom EIS (Figure 2c). Then, the reliability of ion diffusion coef-ficients was further promoted by a galvanostatic intermittenttitration (GITT) test in four electrolytes.57,58 As shown inFigures S8 and S9 in the Supporting Information, the variationof DG calculated from GITT exhibits a “W” type with twominimum regions at x = 0.3−0.5 and x = 1.1−1.3 and a largefluctuation in the x range from 0.6 to 0.9, which corresponds tothe two-step redox reaction of NDI cores in MOFs.59 Thecoefficient values DG of four ions calculated from GITT are lowerbut show a similar trend to those from EIS and CV techniques(for details see the Supporting Information). Compared with thetwo framework structures, the larger pore size in Ni-CHNDI isclearly beneficial for fast diffusion kinetics.Generally, the cations with larger radii have smaller diffusion

coefficients and show poorer solid diffusion because of the stron-ger ion-wall resistance with a crystal framework.60−62 However,compared with other ions with different sizes in the same MOF,it is interesting to find that Na+ has the fastest diffusion coef-ficient and Li+, with a smaller radius, is even slower than thoseof Na+ and TBA+ (Figure 2c). The diffusion coefficient of Al3+

is the smallest despite it having a smaller ionic radius. Theseresults clearly demonstrate that more than one factor affects thediffusion efficiency. First, for all the ions solvated in PC, thesolvated ions show that the TBA+-based solvated radius > Na+-based solvated radius > Li+-based solvated radius > Al3+-basedsolvated radius.63 Then, two main possible reasons are proposed:(1) steric resistance with the pathway induced by the radii ofsolvated species and (2) electrostatic interaction between thecrystal framework and the ions induced by both ion size andcharges of the ions. As shown in Figure 2d, larger cations withbigger solvation radii show a stronger steric effect with a crystalframework.64,65 So TBA+ suffers the strongest resistance withthe diffusion paths; however, the measured trend in diffusionconstant is Na+ > TBA+ > Li+ > Al3+. Another contributingfactor, electrostatic interaction between intercalated cationswith reduced NDI groups, associated with an ion’s valence andits solvated radius, was proposed. Because of the higher valence,Al3+ has an extremely strong electrostatic attraction with thereduced NDI cores in the framework channels, which leads tothe lowest diffusion coefficient.66 Although the radius of solvatedLi+ is smaller than those of Na+ and TBA+, the smaller solvationsphere might show stronger electrostatic attraction with thereduced NDI groups and bind securely with MOFs during theelectrochemical process, which may cause a decline in the Li+-based diffusion coefficient and solid diffusion.50 Similarly, strongelectrostatic attraction caused by the small solvation spherecould be another reason that Al3+ shows the smallest diffusioncoefficient, even though it has the lowest steric stabilizationwith frameworks. Thus, the interesting ion diffusion phenom-enon can possibly be attributed to the special microstructure ofthe MOF. Although a detailed and reasonable discussion hasbeen provided to explain the intercalation mechanism of differ-ent ions, the contrast and quantitative data between differenteffects are not clear and require further experimental supportand discussion.To visually verify the results described above and demonstrate

the application superiority of the MOF with large ion channels inNa+ EC devices, the EC performances of two MOF films were

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investigated in 0.1 M NaClO4/PC, TBAClO4/PC, LiClO4/PC,and Al(ClO4)3/PC solutions. In Figure 3a and Figure S11 inthe Supporting Information, both Ni-BINDI and Ni-CHNDIfilms displayed obvious shifts of the absorbance peak in differentelectrolytes, corresponding to similar reversible color changesfrom transparent to red and finally to dark blue (Figure 3b).This optical conversion is consistent with [NDI] being oxidizedto [NDI]•− and [NDI]2− redox couples.29 Here, the optical con-trast (ΔTmax) of Na

+-based Ni-CHNDI between transparent andblue colors is very high and calculated to be 73% at 720 nm. Thisvalue is much higher than those of other reported Na+-basedEC electrodes.17−19 As shown in Figure S11 in the SupportingInformation, for the other three ion-based electrolytes, the maxi-mum optical contrasts were also located at approximately 720 nmwith MOFs. The TBA+-, Li+-, and Al3+-based optical contrastsof Ni-CHNDI were 49%, 53%, and 27%, respectively, lowerthan that of the Na+ system (Table 1). The ΔTmax of Ni-BINDIwas also obtained in NaClO4 electrolyte (42%) and was foundto be lower than that of Ni-CHNDI because of its much lowerdiffusion coefficient, caused by the narrower channels (33% forTBA+, 29% for Li+, and 21% for Al3+). The results indicate thefast kinetics of Na+ in Ni-CHNDI can lead to a higher modula-tion range than other ion-based systems.The switching time of MOFs is generally characterized as the

period required for 90% of the optical change between thebleached and colored states to occur and is a crucial parameterfor EC devices. As expected, the Na+-based colored and bleachedtimes of the Ni-CHNDI film at 720 nm were calculated to be 2.1and 1.9 s (Figure 3c), which were much faster than reported Na+-based EC materials and other EC MOFs in traditional TBA+-and Li+-based electrolytes (Table S4, Supporting Information)

and also comparable with other cation intercalation EC sys-tems.14,67−72 TBA+-, Li+-, and Al3+-based switching times for theNi-CHNDI film were 4.8 s/4.1 s, 9.1 s/4.9 s, and 11.6 s/9.1 s, i.e.,slower than that of Na+ because of the poorer diffusion kineticsin the channels. In addition, for the Ni-BINDI films, the Na+-based switching times were calculated to be 9.8 s/5.1 s, thefastest among cation-based systems (Figure 3d and Figure S12in the Supporting Information). The changes in switching timescorrespond to the diffusion coefficients described above (Na+ >TBA+ > Li+ > Al3+) among the four ion-based systems. From acomparison of switching performance in two MOFs, Na+ wasfound to not show much advantage compared with the otherthree ions in Ni-BINDI, while the superiority of Na+ emergedin Ni-CHNDI, with larger ion transport channel dimensions.Coloration efficiency, another important parameter for EC mate-

rials, is defined as the change in optical density (OD) per unit

Table 1. EC Properties of Ni-BINDI and Ni-CHNDI Filmsfor Al3+, Li+, Na+, and TBA+ Systems

MOF electrolyteΔTmax(%)a

coloring/bleachingtime (s)b

CE(cm2 C−1)c

Ni-BINDI NaClO4 42 9.8/5.1 113.3/132.0

TBAClO4 33 11.5/6.8 86.2/99.5

LiClO4 29 13.6/6.4 96.7/102.1

Al(ClO4)3 21 14.3/12.9 37.1/42.1

Ni-CHNDI NaClO4 73 2.1/1.9 190.7/260.3

TBAClO4 49 4.8/4.1 164.5/190.1

LiClO4 53 9.1/4.9 112.3/166.2

Al(ClO4)3 27 11.6/9.1 78.9/94.1aOptical contrasts. bColoring/bleaching times at 720 nm measuredbetween biases of −1.5 and 0.5 V. cColoration efficiency at 500/720 nm.

Figure 3. Electrochromic properties of Ni-CHNDI films. (a) UV−vis absorbance spectra of Ni-CHNDI films measured at potentials of 0, −0.6, and−1.1 V, respectively, in 0.1 M NaClO4/PC solution; (b) digital photographs of Ni-CHNDI thin films at different color states compared with realflowers; in situ transmittance responses (at 720 nm) (c) for Ni-CHNDI measured in various 0.1 M electrolytes and (d) for Ni-BINDI andNi-CHNDI films measured in 0.1 M NaClO4/PC solution, respectively, between biases of −1.5 and 0.5 V; (e) OD as a function of chargedensity for (i) Ni-CHNDI films in various 0.1 M electrolytes and for (ii) Ni-BINDI in 0.1 M NaClO4/PC solution; (f) cycling stability ofNi-CHNDI and Ni-CHNDI films (at 720 nm) measured in 0.1 M NaClO4/PC solution.

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of inserted charge.73 Similar to the comparison results for theoptical contrast and switching times, the calculated CE of theNi-CHNDI film for Na+ (260.3 cm2 C−1) is notably higher thanthe values based on TBA+ (190.1 cm2 C−1), Li+ (164.5 cm2 C−1),and Al3+ (94.1 cm2 C−1) at 720 nm (Figure 3e and Table 1).It is also much higher than reported Na+-based EC materials.17−19

In addition, the Ni-CHNDI exhibited a higher CE for Na+ thanNi-BINDI films (132.0 cm2 C−1). The great EC performance ofNi-CHNDI with Na+ can be attributed to two key factors: (1) theone-dimensional acicular morphology of the Ni-CHNDI film and(2) large hexagonal channels in the crystalline structure.74 Theformer increases the contact area between the electrolyte and theactive materials, which leads to an increase in reaction active sitesand a reduction of the ion diffusion path. The latter can speed upthe solid diffusion of cations during insertion and extractionprocesses. As a result, by fabricating the MOF with suitable mor-phology and ion channels, Na+-based EC devices with fast responsespeed, high contrast, and high stability have been achieved.The high CE of Ni-CHNDI for Na+ can result in large optical

modulation with small amounts of insertion or extraction ions,which is beneficial for the long-term cycling stability.16 Therefore,both MOF films exhibited significant redox activity, and noobvious decline at a scan rate of 100 mV s−1 in NaClO4 wasobserved after 500 cycles (Figure S13, Supporting Information).Notably, Ni-CHNDI has great cyclic stability and still maintained91% of optical contrast after 500 repeated cycles in Na+

electrolyte (Figure 3f), which is further confirmed by com-paring the XRD curves before and after EC cycles (Figure S14,Supporting Information). The transparency of Ni-CHNDIfilms was not changed under UV irradiation for up to 100 h inthe air, which is also beneficial for the application of MOFs inoutdoor smart windows (Figure S15, Supporting Information).

To demonstrate the practical applications of a high-performanceMOF-based Na+ EC electrode material in consumer electronics, asolid-state, multicolor EC device with display pixels was fabricatedthrough a mask-free laser writing strategy. As shown in Figure 4a,the solid EC devices were assembled with FTO glass as thecounter electrode and a Na+-based polymer gel as an electrolyte.These devices have a low and practical operation potential rangingfrom −2.5 to 1 V. The different colors of the Ni-CHNDI-Na+-based display pixels are clearly visible with the naked eye(Figure 4b). Also, with the regulation of the drive voltage, the“transparent”, “red”, and “dark blue” colors appear at differentpixels, which suggests potential applications in high-resolution,low-cost, and multicolor displays.The stability of Ni-CHNDI-based devices was further inves-

tigated under different conditions. As shown in Figure S16 ofthe Supporting Information, the coloration performance of thedevices was not affected under UV irradiation for 100 h, corre-sponding to the good light stability of Ni-CHNDI films. Then,the thermal properties of two MOFs and a poly(methyl meth-acrylate) (PMMA)-based electrolyte were studied by thermalgravimetric analysis (TGA), CV test, and in situ transmit-tance responses as shown in Figures S17−S19 (more details inthe Supporting Information); the MOF-based EC layers arestable up to 350 °C. However, the operating temperature of thedevices is limited by the PMMA-based electrolyte (stable at lessthan 100 °C). As shown in Figure S18, the EC redox reactionof the devices can still be carried out at 90 °C. Additionally,Ni-CHNDI-based devices also show good electrochemical sta-bility and maintained 83%, 79%, and 64% of the optical contrastafter 500 repeated electrochemical cycles with PMMA/Na+

as gel electrolyte layer (Figure S19) at 30, 60, and 90 °C,respectively.75

Figure 4. Demonstration of EC devices for applications in consumer electronics and “shared bike” systems. (a) Schematic illustration of thefabrication of the EC device; (b) multicolor Ni-CHNDI-Na+-based display pixels with different voltages; (c) color switching of Ni-CHNDI-Na+-based QRC and detection of the QRC shown on the Ni-CHNDI-Na+-based EC device with a smart phone application; (d) electrochromicQRC devices on shared bikes; (e) antitheft mechanism of EC QRC in cartoon.

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Furthermore, by utilizing the rapid and high-precision laserwriting method, a version-5 QRC with dimensions of 2.5 ×2.5 cm2 was prepared, as shown in Figure 4c and Movie S1 inthe Supporting Information. The embedded code “MOF Na+”can be scanned and readily decoded with software installed on asmart phone. Because of the low cost of Na+-based electrolytes,the fabricated EC-based QRC systems were used as antitheftdevices on the widely popular “shared bikes” in Figure 4d andMovie S2 in the Supporting Information. These devices can bequickly driven by two 1.5 V commercial batteries. As shownin the cartoon in Figure 4e, the QRC appears only when thecustomer pays for the bike using a smart phone-based paymentsystem. Throughout the duration of use, customers can selectdifferent rental conditions by controlling the appearance/disappearance of the QRC, which can serve as an antitheft andsmart management system. The smart QRC in the “shared bike”demonstrates the great application potential of the Na+-basedEC in the IOT.

CONCLUSION

In this contribution, Na+ intercalation electrochromism was dem-onstrated with the utilization of MOF films as a high-efficiencyion transport electrode, exhibiting rapid multicolor switching,high contrast, and high stability. The concept of ion-transportchannel design for electrochromism was clarified by the inten-tional introduction of two kinds of NDI-based MOF films withvarious channel dimensions (radii of approximately 10 and 33 Å).These Na+ intercalation EC films with desired ion-transportchannel dimensions (radii of approximately 33 Å) exhibited fastcolor diversity from transparent to red and then dark blue,accompanied by a high CE up to 260 cm2 C−1, good stabilitywithin 500 cycles, and high optical contrast (ΔT ≈ 73%), whichare the highest in the reported Na+-based EC materials andother MOF EC materials.In addition, a multicolor EC glass with display pixels was

fabricated to demonstrate the potential applications in consumerelectronics. A demonstration of QRC with complicated patternswas done by mask-free laser writing for application in the IOT.The significance of this work includes the following: (1) theconcept of designing ion-transport pathways for EC can bewidely adopted for the design of high-performance ion-transport electrodes; (2) a high-performance Na+ intercalationEC was demonstrated, which provides the approach for low-cost, high-efficiency EC devices for applications in consumerelectronics and the IOT.

EXPERIMENTAL SECTIONChemicals. All solvents were further dried using 3 Å molecular

sieves for 48 h. Ultrapure water (18.2 MΩ cm) was obtained from aMilli-Q water purification system (Millipore Corp., Bedford, MA,USA) unless stated otherwise. The FTO conductive glass (15 Ω/sq,Nippon Sheet Glass, Hyogo, Japan) was sequentially washed throughultrasonic treatment in detergent, acetone, ethanol, and deionizedwater. 1,4,5,8-Naphthalenetetracarboxylic dianhydride (Sigma-Aldrich),5-aminoisophthalic acid (TCL, 98%), 5-amino-2-hydroxybenzoic acid(TCL, 98%), NaClO4 (Alfa, 98%), Al(ClO4)3 (Adamas, 99%), LiClO4(Adamas, 99%), and TBAClO4 (Adamas, 98%) were used as receivedwithout further purification.Synthesis of N,N-Bis(5-isophthalic acid)naphthalenediimide

(H4BINDI) and N ,N-Bis(3-carboxy-4-hydroxyphenyl)-naphthalenediimide (H4CHNDI). N,N-Bis(5-isophthalic acid)-naphthalenediimide (H4BINDI) was synthesized according to the pre-vious report (Scheme S1, Supporting Information).40 Briefly, 1,4,5,8-tetracarboxy dianhydride (1.34 g, 5.0 mM) and 5-aminoisophthalic

acid (1.81 g, 10.0 mM) were added into 100 mL of acetic acid and refluxedfor 12 h. After cooling to room temperature the product was collectedby filtration and recrystallized from dimethylformamide (DMF) (80%).1H NMR (600 MHz, DMSO-d6, δ): 8.74 (s, 4H, Ar H), 8.59 (s, 2H,Ar H), 8.33 (s, 4H, Ar H) (Figure S4, Supporting Information). ForN,N-bis(3-carboxy-4-hydroxyphenyl)naphthalenediimide (H4CHNDI),100 mL of anhydrous DMF was charged with 1,4,5,8-naphthalenete-tracarboxylic dianhydride (1.34 g, 5.0 mM) and 5-amino-2-hydrox-ybenzoic acid (1.53 g, 10.0 mM), under a nitrogen atmosphere. Thereaction mixture was heated and stirred for 12 h, and the orange sus-pension was filtered off, washed with methanol, and then recrystallizedfrom DMF (65%). 1H NMR (600 MHz, DMSO-d6, δ): 8.72 (s, 4H,Ar H), 7.92 (s, 2H, Ar H), 7.58 (d, 2H, Ar H), 7.12 (d, 2H, Ar H)(Figure S5, Supporting Information).

Preparation of the Ni-BINDI and Ni-CHNDI Powder. To pre-pare Ni-BINDI, briefly, Ni(NO3)2·6H2O (0.29 g, 1 mM), 20 mL ofmixed DMF solution containing H4BINDI (0.36 g, 0.6 mM), and1 mL of 12 M HNO3 were added into a 50 mL Teflon-lined stainless-steel autoclave. Then, the autoclave was sealed and maintained in agravity convection oven at 130 °C for 24 h. For Ni-CHNDI,H4CHNDI (0.29 g, 0.5 mM), Ni(NO3)2·6H2O (0.29 g, 1 mM), and1 mL of methanol were added into 20 mL of DMF solution; then themixture was poured into the 50 mL autoclave at 130 °C for 24 h. Aftercooling to room temperature, the MOF powders were washed withDMF solution and then soaked in a methanol solution for 3 days, andfresh methanol was added every day before use.

Preparation of the Ni-BINDI and Ni-CHNDI Thin Film. To pre-pare Ni-BINDI, Ni(NO3)2·6H2O (0.15 g, 0.5 mM), 20 mL of mixedDMF solution containing H4BINDI (0.12 g, 0.2 mM), and 0.5 mL of12 M HNO3 as modulator were added into a 50 mL Teflon-linedstainless-steel autoclave, and the FTO glass was vertically submergedin the solution. Then, the autoclave was sealed and maintained in agravity convection oven at 130 °C for 50 min. For Ni-CHNDI,H4CHNDI (0.18 g, 0.2 mM), Ni(NO3)2·6H2O (0.15 g, 0.5 mM), and1 mL of methanol were added into 20 mL of a DMF solution; then themixture was poured into the 50 mL autoclave at 130 °C for 30 min.After cooling to room temperature, the FTO glass with MOF films waswashed with DMF solution and then soaked in a methanol solution for3 days, and fresh methanol was added every day before use.

Assembly of the Electrochromic Device. The MOF electrodeswere patterned by a pulsed CO2 laser, and the vector patterns weredesigned using CorelDraw software. The polymer gel electrolytecontained 0.1 M NaClO4 in PC solution and 20 wt % PMMA (relativeto the NaClO4 solution). ECDs were fabricated by inserting a Scotchtape spacer between the FTO electrodes, followed by injecting apolymer gel between the two electrodes.

Structure Simulation. The structure of Ni-BINDI was simulatedfrom the reported structure of Ca-NDI (CCDC 888794) and Sr-NDI(CCDC 1412539), but slightly different in unit cell sizes.40,41 Briefly,Ni2+ was introduced in place of the Ca2+ or Sr2+ in the reported MOFs.The matching analyses and the unit cell parameter refinement werecarried out by Materials Studio (v.8.0.0.843, 2014; Accelrys Software).The simulated XRD and structure are in the I41/a space group(see Table S1 for details). The structure of Ni-CHNDI was simulatedform reported Ni-NDISA.29 [CCDC 1585026 contains the supple-mentary crystallographic data for this paper. These data can be obtainedfree of charge from the Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif.]

Characterization. FTO glass with MOF films was cut into squaresof 1 cm2; then electrochemical measurements were carried out in a PCsolution containing 0.1 M electrolyte using three-electrode electro-chemical cells with the FTO substrate as the working electrode,platinum mesh as the counter electrode, and freshly prepared Ag/AgClas the pseudoreference electrode. EIS was conducted by an electro-chemical workstation (Biologic SAS, VSP-300) over a frequency rangeof 100 mHz to 1000 kHz. CV of the cells was measured by a CHI760D(Shanghai Chenhua Instruments, China) electrochemical measure-ment system. In the GITT, the films were rested for 5 h to reachequilibrium potential (E0) before the test; then a l mA cathodic currentpulse was continued for 0.5 s, and the relaxation time before the next

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current pulse was 100 s. The potential drifted less than 10 mV duringthe last relaxation.The XRD patterns were measured using an X-ray diffractometer

(D/max 2550 V, Rigaku, Japan, Cu Ka (λ = 0.154 nm) radiation at40 kV and 200 mA). The morphology of the samples was characterizedby field emission scanning electron microscopy (S-4800, Hitachi, Japan).High-resolution transmission electron microscopy images were obtainedusing a JEM 2100 F (JEOL, Tokyo, Japan) operating at 50 kV. 1H NMRspectra were recorded on an Avance3hd 600 MHz spectrometer(Bruker, Switzerland). The obtained product was dissolved in d6-DMSOfor NMR measurement. The UV−vis spectra of the samples werecollected at room temperature with a spectrophotometer (model Lambda950, PerkinElmer Co., USA). The nitrogen adsorption−desorptionisotherms of samples were measured using an automatic volumetricsorption analyzer (ASAP 2020, Micromeritics, USA) at liquid-nitrogentemperature, 77 K. Prior to the N2 adsorption−desorption measure-ment, all samples were degassed at 150 °C under vacuum for 24 h toremove impurities. TGA was measured from a Q5000IR equipment(TA Instruments, USA). During analysis the MOF samples wereheated from 50 to 600 °C in an air atmosphere at a constant rate of10 °C/min. The UV radiation of the MOF films was performed undera hand-held ultraviolet lamp (16 W, 372 nm).

ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acsnano.8b00974.

Figures S1−S19 and electrochemistry/electrochromicperformance of MOFs and comparison of MOFs andNa+-based EC materials (PDF)Movie of the MOF-based QRC device (AVI)Movie of the MOF-based QRC device (AVI)X-ray crystallographic file of the Ni-BINDI structure(CIF)

AUTHOR INFORMATIONCorresponding Authors*E-mail (G. Wang): wanggang070501@hotmail.com.*E-mail (H. Wang): wanghz@dhu.edu.cn.ORCIDYao Chen: 0000-0003-4414-8528Chengyi Hou: 0000-0003-4142-2982Hongzhi Wang: 0000-0002-5469-2327Author Contributions#R. Li and K.-R. Li contributed equally to this work.NotesThe authors declare no competing financial interest.

ACKNOWLEDGMENTSWe gratefully acknowledge the mentorship, support, and valuablediscussion from Prof. Elsa Reichmanis at Georgia Institute ofTechnology and the financial support of the NSF of China(51672043), MOE of China (111-2-04, IRT_16R13), STC ofShanghai (16JC1400700, 16XD1400100), SMEC (2017-01-07-00-03-E00055), and Eastern Scholar.

REFERENCES(1) Hwang, J. Y.; Myung, S. T.; Sun, Y. K. Sodium-Ion Batteries:Present and Future. Chem. Soc. Rev. 2017, 46, 3529−3614.(2) Kim, M. S.; Lim, E.; Kim, S.; Jo, C.; Chun, J.; Lee, J. GeneralSynthesis of N-Doped Macroporous Graphene-Encapsulated Meso-porous Metal Oxides and Their Application as New Anode Materialsfor Sodium-Ion Hybrid Supercapacitors. Adv. Funct. Mater. 2017, 27,1603921.

(3) Wang, X.; Kajiyama, S.; Iinuma, H.; Hosono, E.; Oro, S.;Moriguchi, I.; Okubo, M.; Yamada, A. Pseudocapacitance of MXeneNanosheets for High-Power Sodium-Ion Hybrid Capacitors. Nat.Commun. 2015, 6, ncomms7544.(4) Dall’Agnese, Y.; Taberna, P. L.; Gogotsi, Y.; Simon, P. Two-Dimensional Vanadium Carbide (MXene) as Positive Electrode forSodium-Ion Capacitors. J. Phys. Chem. Lett. 2015, 6, 2305−2309.(5) Niklasson, G. A.; Granqvist, C. G. Electrochromics for SmartWindows: Thin Films of Tungsten Oxide and Nickel Oxide, andDevices Based on These. J. Mater. Chem. 2006, 17, 127−156.(6) Wang, J. L.; Lu, Y. R.; Li, H. H.; Liu, J. W.; Yu, S. H. Large AreaCo-Assembly of Nanowires for Flexible Transparent Smart Windows.J. Am. Chem. Soc. 2017, 139, 9921−9926.(7) Yao, Z.; Di, J.; Yong, Z.; Zhao, Z.; Li, Q. Aligned CoaxialTungsten Oxide-carbon Nanotube Sheet: A Flexible and GradientElectrochromic Film. Chem. Commun. 2012, 48, 8252−8254.(8) Cai, G.; Wang, J.; Lee, P. S. Next-Generation MultifunctionalElectrochromic Devices. Acc. Chem. Res. 2016, 49, 1469−1476.(9) Yan, C.; Kang, W.; Wang, J.; Cui, M.; Wang, X.; Foo, C. Y.; Chee,K. J.; Lee, P. S. Stretchable and Wearable Electrochromic Devices. ACSNano 2014, 8, 316−322.(10) Mortimer, R. J.; Dyer, A. L.; Reynolds, J. R. ElectrochromicOrganic and Polymeric Materials for Display Applications. Displays2006, 27, 2−18.(11) Heckner, K. H.; Kraft, A. Similarities between ElectrochromicWindows and Thin Film Batteries. Solid State Ionics 2002, 152, 899−905.(12) Xia, X.; Ku, Z.; Zhou, D.; Zhong, Y.; Zhang, Y.; Wang, Y.; JoonHuang, M.; Tu, J.; Jin Fan, H. Perovskite Solar Cell PoweredElectrochromic Batteries for Smart Windows. Mater. Horiz. 2016, 3,588−595.(13) Wei, D.; Scherer, M. R. J.; Bower, C.; Andrew, P.; Ryhanen, T.;Steiner, U. A Nanostructured Electrochromic Supercapacitor. NanoLett. 2012, 12, 1857−1862.(14) Tian, Y.; Zhang, W.; Cong, S.; Zheng, Y.; Geng, F.; Zhao, Z.Unconventional Aluminum Ion Intercalation/Deintercalation for FastSwitching and Highly Stable Electrochromism. Adv. Funct. Mater.2015, 25, 5833−5839.(15) Yoo, S. J.; Lim, J. W.; Sung, Y. E.; Jung, Y. H.; Choi, H. G.; Kim,D. K. Fast Switchable Electrochromic Properties of Tungsten OxideNanowire Bundles. Appl. Phys. Lett. 2007, 90, 173126.(16) Brezesinski, T.; Fattakhova Rohlfing, D.; Sallard, S.; Antonietti,M.; Smarsly, B. M. Highly Crystalline WO3 Thin Films with Ordered3D Mesoporosity and Improved Electrochromic Performance. Small2006, 2, 1203−1211.(17) Dini, D.; Decker, F.; Masetti, E. A Comparison of theElectrochromic Properties of WO3 Films Intercalated with H+, Li+ andNa+. J. Appl. Electrochem. 1996, 26, 647−653.(18) Patel, K. J.; Panchal, C. J.; Desai, M. S.; Mehta, P. K. AnInvestigation of the Insertion of the Cations H+, Na+, K+ on theElectrochromic Properties of the Thermally Evaporated WO3 ThinFilms Grown at Different Substrate Temperatures. Mater. Chem. Phys.2010, 124, 884−890.(19) Fernandes, M.; Leones, R.; Pereira, S.; Costa, A. M. S.; Mano, J.F.; Silva, M. M.; Fortunato, E.; de Zea Bermudez, V.; Rego, R. Eco-Friendly Sol-Gel Derived Sodium-Based Ormolytes for ElectrochromicDevices. Electrochim. Acta 2017, 232, 484−494.(20) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. TheChemistry and Applications of Metal-Organic Frameworks. Science2013, 341, 1230444.(21) Lin, X.; Blake, A. J.; Wilson, C.; Sun, X. Z.; Champness, N. R.;George, M. W.; Hubberstey, P.; Mokaya, R.; Schroder, M. A PorousFramework Polymer Based on a Zinc(II) 4,4‘-Bipyridine-2,6,2‘,6‘-Tetracarboxylate: Synthesis, Structure, and “Zeolite-Like” Behaviors. J.Am. Chem. Soc. 2006, 128, 10745−10753.(22) Kornienko, N.; Zhao, Y.; Kley, C. S.; Zhu, C.; Kim, D.; Lin, S.;Chang, C. J.; Yaghi, O. M.; Yang, P. Metal-Organic Frameworks forElectrocatalytic Reduction of Carbon Dioxide. J. Am. Chem. Soc. 2015,137, 14129−14135.

ACS Nano Article

DOI: 10.1021/acsnano.8b00974ACS Nano 2018, 12, 3759−3768

3766

(23) Patwardhan, S.; Schatz, G. C. Theoretical Investigation ofCharge Transfer in Metal Organic Frameworks for ElectrochemicalDevice Applications. J. Phys. Chem. C 2015, 119, 24238−24247.(24) Aubrey, M. L.; Long, J. R. A Dual-Ion Battery Cathode viaOxidative Insertion of Anions in a Metal-Organic Framework. J. Am.Chem. Soc. 2015, 137, 13594−13602.(25) Ameloot, R.; Aubrey, M.; Wiers, B. M.; Gomora-Figueroa, A. P.;Patel, S. N.; Balsara, N. P.; Long, J. R. Ionic Conductivity in the Metal-Organic Framework UiO-66 by Dehydration and Insertion of LithiumTert-Butoxide. Chem. - Eur. J. 2013, 19, 5533−5536.(26) Wade, C. R.; Li, M.; Dinca, M. Facile Deposition ofMulticolored Electrochromic Metal-Organic Framework Thin Films.Angew. Chem., Int. Ed. 2013, 52, 13377−13381.(27) Kung, C. W.; Wang, T. C.; Mondloch, J. E.; Fairen-Jimenez, D.;Gardner, D. M.; Bury, W.; Klingsporn, J. M.; Barnes, J. C.; Van Duyne,R.; Stoddart, J. F.; Wasielewski, M. R.; Farha, O. K.; Hupp, J. T. Metal-Organic Framework Thin Films Composed of Free-Standing AcicularNanorods Exhibiting Reversible Electrochromism. Chem. Mater. 2013,25, 5012−5017.(28) Xie, Y. X.; Zhao, W.-N.; Li, G. C.; Liu, P. F.; Han, L. A.Naphthalenediimide-Based Metal-Organic Framework and Thin FilmExhibiting Photochromic and Electrochromic Properties. Inorg. Chem.2016, 55, 549−551.(29) AlKaabi, K.; Wade, C. R.; Dinca, M. Transparent-to-DarkElectrochromic Behavior in Naphthalene-Diimide-Based MesoporousMOF-74 Analogs. Chem. 2016, 1, 264−272.(30) Mjejri, I.; Doherty, C. M.; Rubio-Martinez, M.; Drisko, G. L.;Rougier, A. Double-Sided Electrochromic Device Based on Metal-Organic Frameworks. ACS Appl. Mater. Interfaces 2017, 9, 39930−39934.(31) Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dotz,F.; Kastler, M.; Facchetti, A. A High-Mobility Electron-TransportingPolymer for Printed Transistors. Nature 2009, 457, 679−686.(32) Alvey, P. M.; Ono, R. J.; Bielawski, C. W.; Iverson, B. L.Conjugated NDI-Donor Polymers: Exploration of Donor Size andElectrostatic Complementarity. Macromolecules 2013, 46, 718−726.(33) Wurthner, F.; Ahmed, S.; Thalacker, C.; Debaerdemaeker, T.Core-Substituted Naphthalene Bisimides: New Fluorophors withTunable Emission Wavelength for FRET Studies. Chem. - Eur. J.2002, 8, 4742−4750.(34) Wang, G.; Persson, N.; Chu, P.-H.; Kleinhenz, N.; Fu, B.;Chang, M.; Deb, N.; Mao, Y.; Wang, H.; Grover, M. A. MicrofluidicCrystal Engineering of π-Conjugated Polymers. ACS Nano 2015, 9,8220−8230.(35) Naab, B. D.; Gu, X.; Kurosawa, T.; To, J. W. F.; Salleo, A.; Bao,Z. Role of Polymer Structure on the Conductivity of N-DopedPolymers. Adv. Electron. Mater. 2016, 2, 1600004.(36) Zhan, X.; Facchetti, A.; Barlow, S.; Marks, T. J.; Ratner, M. A.;Wasielewski, M. R.; Marder, S. R. Rylene and Related Diimides forOrganic Electronics. Adv. Mater. 2011, 23, 268−284.(37) Wang, G.; Huang, W.; Eastham, N. D.; Fabiano, S.; Manley, E.F.; Zeng, L.; Wang, B.; Zhang, X.; Chen, Z.; Li, R.; Chang, R. P. H.;Chen, L. X.; Bedzyk, M. J.; Melkonyan, F. S.; Facchetti, A.; Marks, T. J.Aggregation Control in Natural Brush-Printed Conjugated PolymerFilms and Implications for Enhancing Charge Transport. Proc. Natl.Acad. Sci. U. S. A. 2017, 114, E10066−E10073.(38) Bhosale, S. V.; Jani, C. H.; Langford, S. J. Chemistry ofNaphthalene Diimides. Chem. Soc. Rev. 2008, 37, 331−342.(39) Olivier, Y.; Niedzialek, D.; Lemaur, V.; Pisula, W.; Mullen, K.;Koldemir, U.; Reynolds, J. R.; Lazzaroni, R.; Cornil, J.; Beljonne, D.25th Anniversary Article: High-Mobility Hole and Electron TransportConjugated Polymers: How Structure Defines Function. Adv. Mater.2014, 26, 2119−2136.(40) Garai, B.; Mallick, A.; Banerjee, R. Photochromic Metal-organicFrameworks for Inkless and Erasable Printing. Chem. Sci. 2016, 7,2195−2200.(41) Han, L.; Qin, L.; Xu, L.; Zhou, Y.; Sun, J.; Zou, X. A NovelPhotochromic Calcium-Based Metal-Organic Framework Derived

from a Naphthalene Diimide Chromophore. Chem. Commun. 2013,49, 406−408.(42) Deng, H.; Grunder, S.; Cordova, K. E.; Valente, C.; Furukawa,H.; Hmadeh, M.; Gandara, F.; Whalley, A. C.; Liu, Z.; Asahina, S.;Kazumori, H.; O’Keeffe, M.; Terasaki, O.; Stoddart, J. F.; Yaghi, O. M.Large-Pore Apertures in a Series of Metal-Organic Frameworks. Science2012, 336, 1018−1023.(43) Sun, D.; Ma, S.; Ke, Y.; Collins, D. J.; Zhou, H.-C. AnInterweaving MOF with High Hydrogen Uptake. J. Am. Chem. Soc.2006, 128, 3896−3897.(44) Setoyama, N.; Kaneko, K.; Rodriguez-Reinoso, F. Ultra-micropore Characterization of Microporous Carbons by Low-Temper-ature Helium Adsorption. J. Phys. Chem. 1996, 100, 10331−10336.(45) Terzyk, A. P.; Gauden, P. A.; Kowalczyk, P. What Kind of PoreSize Distribution Is Assumed in the Dubinin-Astakhov AdsorptionIsotherm Equation? Carbon 2002, 40, 2879−2886.(46) Zhou, Y.; Wang, J.; Hu, Y.; O’Hayre, R.; Shao, Z. A PorousLiFePO4 and Carbon Nanotube Composite. Chem. Commun. 2010,46, 7151−7153.(47) Levi, M. D.; Aurbach, D. Diffusion Coefficients of Lithium Ionsduring Intercalation into Graphite Derived from the SimultaneousMeasurements and Modeling of Electrochemical Impedance andPotentiostatic Intermittent Titration Characteristics of Thin GraphiteElectrodes. J. Phys. Chem. B 1997, 101, 4641−4647.(48) DeBlase, C. R.; Hernandez-Burgos, K.; Rotter, J. M.; Fortman,D. J.; dos S. Abreu, D.; Timm, R. A.; Diogenes, I. C. N.; Kubota, L. T.;Abruna, H. D.; Dichtel, W. R. Cation-Dependent Stabilization ofElectrogenerated Naphthalene Diimide Dianions in Porous PolymerThin Films and Their Application to Electrical Energy Storage. Angew.Chem., Int. Ed. 2015, 54, 13225−13229.(49) Shao, Y.; El-Kady, M. F.; Lin, C.-W.; Zhu, G.; Marsh, K. L.;Hwang, J. Y.; Zhang, Q.; Li, Y.; Wang, H.; Kaner, R. B. 3D Freeze-Casting of Cellular Graphene Films for Ultrahigh-Power-DensitySupercapacitors. Adv. Mater. 2016, 28, 6719−6726.(50) Amin, M. A. Weight Loss, Polarization, ElectrochemicalImpedance Spectroscopy, SEM and EDX studies of the CorrosionInhibition of Copper in Aerated NaCl Solutions. J. Appl. Electrochem.2006, 36, 215−226.(51) Hauch, A.; Georg, A. Diffusion in the Electrolyte and Charge-Transfer Reaction at the Platinum Electrode in Dye-Sensitized SolarCells. Electrochim. Acta 2001, 46, 3457−3466.(52) Xiao, P.; Lv, T.; Chen, X.; Chang, C. LiNi0.8Co0.15Al0.05O2:Enhanced Electrochemical Performance from Reduced CationicDisordering in Li Slab. Sci. Rep. 2017, 7, 1408.(53) Ammar, F.; Saveant, J. M. Convolution Potential SweepVoltammetry: II. Multistep Nernstian Waves. J. Electroanal. Chem.Interfacial Electrochem. 1973, 47, 215−221.(54) Phelps, J.; Bard, A. J. One- vs. Two-Electron Oxidations ofTetraarylethylenes in Aprotic Solvents. J. Electroanal. Chem. InterfacialElectrochem. 1976, 68, 313−335.(55) Howlett, P. C.; MacFarlane, D. R.; Hollenkamp, A. F. HighLithium Metal Cycling Efficiency in a Room-Temperature IonicLiquid. Electrochem. Solid-State Lett. 2004, 7, A97−A101.(56) Guarr, T. F.; Anson, F. C. Electropolymerization of Ruthenium(Bis (1, 10-Phenanthroline) (4-Methyl-4’-Vinyl2, 2’-Bipyridine)Complexes through Direct Attack on the Ligand Ring System. J.Phys. Chem. 1987, 91, 4037−4043.(57) Dees, D. W.; Kawauchi, S.; Abraham, D. P.; Prakash, J. Analysisof the Galvanostatic Intermittent Titration Technique (GITT) asApplied to a Lithium-Ion Porous Electrode. J. Power Sources 2009, 189,263−268.(58) Macrelli, G.; Poli, E. Mixed Cerium/Titanium and Cerium/Zirconium Oxides as Thin Film Counter Electrodes for All Solid StateElectrochromic Transmissive Devices. Electrochim. Acta 1999, 44,3137−3147.(59) Ding, N.; Xu, J.; Yao, Y. X.; Wegner, G.; Fang, X.; Chen, C. H.;Lieberwirth, I. Determination of the Diffusion Coefficient of LithiumIons in Nano-Si. Solid State Ionics 2009, 180, 222−225.

ACS Nano Article

DOI: 10.1021/acsnano.8b00974ACS Nano 2018, 12, 3759−3768

3767

(60) Dennis, J. R.; Hale, E. B. Crystalline to AmorphousTransformation in Ion-Implanted Silicon: A Composite Model. J.Appl. Phys. 1978, 49, 1119−1127.(61) Yung-Fang, Y. Y.; Kummer, J. T. Ion Exchange Properties of andRates of Ionic Diffusion in Beta-Alumina. J. Inorg. Nucl. Chem. 1967,29, 2453−2475.(62) Lunell, S.; Stashans, A.; Ojamae, L.; Lindstrom, H.; Hagfeldt, A.Li and Na Diffusion in TiO2 from Quantum Chemical Theory versusElectrochemical Experiment. J. Am. Chem. Soc. 1997, 119, 7374−7380.(63) Pilon, L.; Wang, H.; d’Entremont, A. Recent Advances inContinuum Modeling of Interfacial and Transport Phenomena inElectric Double Layer Capacitors. J. Electrochem. Soc. 2015, 162,5158−5178.(64) Chmiola, J.; Yushin, G.; Gogotsi, Y.; Portet, C.; Simon, P.;Taberna, P. L. Anomalous Increase in Carbon Capacitance at PoreSizes Less Than 1 Nanometer. Science 2006, 313, 1760−1763.(65) Galhena, D. T. L.; Bayer, B. C.; Hofmann, S.; Amaratunga, G. A.J. Understanding Capacitance Variation in Sub-Nanometer Pores by inSitu Tuning of Interlayer Constrictions. ACS Nano 2016, 10, 747−754.(66) Li, K.; Shao, Y.; Liu, S.; Zhang, Q.; Wang, H.; Li, Y.; Kaner, R. B.Aluminum-Ion-Intercalation Supercapacitors with Ultrahigh ArealCapacitance and Highly Enhanced Cycling Stability: Power Supplyfor Flexible Electrochromic Devices. Small 2017, 13, 1700380.(67) Cong, S.; Tian, Y.; Li, Q.; Zhao, Z.; Geng, F. Single-CrystallineTungsten Oxide Quantum Dots for Fast Pseudocapacitor andElectrochromic Applications. Adv. Mater. 2014, 26, 4260−4267.(68) Elool Dov, N.; Shankar, S.; Cohen, D.; Bendikov, T.; Rechav,K.; Shimon, L. J. W.; Lahav, M.; van der Boom, M. E. ElectrochromicMetallo-Organic Nanoscale Films: Fabrication, Color Range, andDevices. J. Am. Chem. Soc. 2017, 139, 11471−11481.(69) Koo, B.-R.; Ahn, H. J. Fast-Switching Electrochromic Propertiesof Mesoporous WO3 Films with Oxygen Vacancy Defects. Nanoscale2017, 9, 17788−17793.(70) Thummavichai, K.; Trimby, L.; Wang, N.; Wright, C. D.; Xia, Y.;Zhu, Y. Low Temperature Annealing Improves the Electrochromicand Degradation Behavior of Tungsten Oxide (WOx) Thin Films. J.Phys. Chem. C 2017, 121, 20498−20506.(71) Yuan, G.; Hua, C.; Huang, L.; Defranoux, C.; Basa, P.; Liu, Y.;Song, C.; Han, G. Optical Characterization of the Coloration Processin Electrochromic Amorphous and Crystalline WO3 Films bySpectroscopic Ellipsometry. Appl. Surf. Sci. 2017, 421, 630−635.(72) Ghosh, K.; Roy, A.; Tripathi, S.; Ghule, S.; Singh, A. K.;Ravishankar, N. Insights into Nucleation, Growth and Phase Selectionof WO3: Morphology Control and Electrochromic Properties. J. Mater.Chem. C 2017, 5, 7307−7316.(73) Gaupp, C. L.; Welsh, D. M.; Rauh, R. D.; Reynolds, J. R.Composite Coloration Efficiency Measurements of ElectrochromicPolymers Based on 3,4-Alkylenedioxythiophenes. Chem. Mater. 2002,14, 3964−3970.(74) Lee, S. H.; Deshpande, R.; Parilla, P. A.; Jones, K. M.; To, B.;Mahan, A. H.; Dillon, A. C. Crystalline WO3 Nanoparticles for HighlyImproved Electrochromic Applications. Adv. Mater. 2006, 18, 763−766.(75) Chen, X.; Shen, X.; Li, B.; Peng, H. J.; Cheng, X. B.; Li, B. Q.;Zhang, X. Q.; Huang, J. Q.; Zhang, Q. Ion-Solvent ComplexesPromote Gas Evolution from Electrolytes on a Sodium Metal Anode.Angew. Chem., Int. Ed. 2018, 57, 734−737.

ACS Nano Article

DOI: 10.1021/acsnano.8b00974ACS Nano 2018, 12, 3759−3768

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