Enhanced Energy Harvesting by Concentration. Gradient-Driven Ion Transport in SBA-15 Mesoporous

Transcription

1 Eletroni Supplementary aterial (ESI) for ab on a Chip. This journal is The Royal Soiety of Chemistry 016 Eletroni supplementary information (ESI) Enhaned Energy arvesting by Conentration Gradient-Driven Ion Transport in SBA-15 esoporous Silia Thin Films Junho wang* a,b, Sho Kataoka b,, Akira Endo b, and irofumi Daiguji a,b a Department of ehanial Engineering, Graduate Shool of Engineering, The University of Tokyo, ongo, Bunkyo-ku, Tokyo , Japan b CREST, Japan Siene and Tehnology Ageny (JST), 7 Gobanho, Chiyoda-ku, Tokyo -0076, Japan National Institute of Advaned Industrial Siene and Tehnology (AIST), AIST Tsukuba Central 5-, igashi, Tsukuba, Ibaraki , Japan Table of Contents S1. Fabriation of the nanofluidi devie with an SBA-15 PS thin film S. Equivalent iruit model for energy harvesting harateristis 6 S3. easurement of redox potential differene 9 S4. Ativity oeffiients for alulating the redox potentials 11 S5. Effet of weak ion onentration solutions on p max and η max 14 S1

2 S1. Fabriation of the nanofluidi devie with an SBA-15 PS thin film The nanofluidi devie was fabriated by bonding the mirostrutured-pds hip embossed by the soft lithography (Replia miromolding) to the Si hip on whih a patterned PS thin film was overed with a SiO layer resulting in two reservoirs formed on both sides of the patterned PS thin film. Fig. S1 shows a shemati illustration of the fabriation proedure for the nanofluidi devie whih has a built-in PS thin film with uniaxially aligned nanopores. Firstly, the as-prepared PS thin film on the Si substrate (Stage 1) was overed with a positive photoresist (OFPR P, Tokyo Ohka Kogyo Co., td., Japan) layer of ~ 6.5 µm using a spinoating method, then exposed by maskless arbitrary optial miro-pattern generator to form the retangular pattern (1 mm in length 300 µm in width), and developed in an aqueous alkali solution (ND-3, Tokyo Ohka Kogyo Co., td., Japan) for 90 s to obtain an upper layer pattern (Stage ). In the following plasma hemial vapor deposition proess (Stage 5), some deposits may be reated inside the nanopores. To trunate the edge of the nanopore array, the width of the retangular pattern here is larger than that of the final retangular patterned PS (1 mm in length 0 µm in width). The resulting upper photoresist layer pattern was hard baked at 383 K for 300 s to produe a robust masking layer. Then, the retangular mask patterned PS thin film was formed by CF 4 /O plasma reative ion ething, RIE, (SACO RIE-00, Japan) at 80 W and 5 Pa for 60 s (Stage 3). Afterwards, the remaining photoresist layer was stripped off using an aetone remover (Wako Pure Chemistry Industries, td., Japan) (Stage 4), then it was rinsed with DI water in the ultrasoni bath for 3 min, and the sample was hard baked at 383 K for 300 s again. Seondly, a SiO layer of ~0 nm in thikness was deposited onto the entire area inluding the patterned PS thin film via plasma hemial vapor deposition, PCVD, (SACO PCVD PD-0SS, Japan) (Stage 5). Subsequently, the aforementioned mask pattern proess on the substrate with the deposited SiO thin layer was ompleted to make two reservoirs (1 mm in width 3 mm in length) on S

3 both sides of the patterned retangular PS thin film in the same way. The distane between reservoirs is 0 µm and idential with the width of the final retangular pattern (Stage 6). The RIE proess was then performed in the CF 4 /O plasma at 80 W and 5 Pa for 10 s to eth the deposited SiO layer (Stage 7) and sequentially in the SF 6 /O plasma at 80 W and 5 Pa for 480 s to eth a layer of ~ 1 µm in depth on the Si substrates (Stage 8). Afterwards, the remaining photoresist layer was stripped off using the aetone remover (Stage 9), then it was rinsed with DI water in the ultrasoni bath for 3 min, and the sample was hard baked at 383 K for 300 s again. Finally, the 1st mirostrutured-pds hip and nd PDS hip for injeting aqueous solutions were bonded onto the patterned substrate with the PS thin film by a wet-pds bonding method (Stage ). Figure S1. Shemati illustration of the fabriation proedure of the nanofluidi devie with the PS thin film of the uniaxially aligned nanopores. S3

4 Fig. S (a) and (b) show a top view and a ross-setional view of PDS hips produed by the soft lithography (replia miro-molding method), respetively. There are four holes (1 mm in diameter) for effetively injeting aqueous solutions. Two inlet holes were formed on eah reservoir using a 1 mmdiameter disposable biopsy punh with a plunger system (Kai Industries Co. td., Japan). The size of eah reservoir is 3 mm in length, 1 mm in width, and 0 µm in height. The distane between the two reservoirs is 50 µm. The seond PDS hip shown in Fig. S () and (d) has muh larger reservoirs and the size is 8 mm in length, 3.5 mm in width, and 5 mm in height. Figure S. Shemati diagram of the PDS hip. (a) Top view and (b) ross setional view (at A 1 -Á 1 line) of the first mirostrutured PDS hip with four drilled holes for injeting aqueous solutions, and () top view and (d) ross-setional view (at A -Á line) of the seond PDS hip with two retangular reservoirs. S4

5 The as-prepared PDS hips were leaned with isopropanol (Wako Pure Chemistry Industries, td., Japan) in the ultrasoni bath for 600 s. The sample was dried using a nitrogen gun and then plaed in a lean room at room temperature for 4 hours. Afterwards, a PDS monomer/uring agent mixture (:1 wt/wt %) was spread on a lean silion substrate by a spin oater at 7500 rpm for 10 s, yielding a thin layer of wet PDS (a. 5 µm in thikness). The bonding side of the PDS hip was diretly applied to the wet PDS layer, and thus the bonding surfae was oated with the wet PDS. Within half an hour, the PDS hips were arefully aligned and bonded onto the patterned substrate using a stereomirosope (model SZ-00, Nikon Instruments In., Japan) and a miro manipulator (-15 model, Narishige, Japan). The ombined hip was then ured in a onvetion oven at 353 K for 1 hour to ompletely seal the whole devie. S5

6 S. Equivalent iruit model for energy harvesting harateristis Fig. S3 (a) shows the equivalent iruit representing the experimental setup. The eletri potential generated in nanopores, V, is given by V V out V redox V o IR, (S1) where I is the ioni urrent, V out is the voltage output from a soure meter, V redox is the potential differene between two Ag/AgCl eletrodes due to the redox reations, V o is the open-iruit voltage due to the ion-seletive property, and R is internal resistane of nanopores, respetively. V redox is aused by an unequal potential drop at the two eletrodes and given by the Nernst equation: S1 V redox RT ln zf, (S) where R, T, z, F, and γ are the gas onstant, temperature, valene, Faraday onstant, and ativity oeffiient, respetively. In this study, V redox was measured using different ombinations of and and the measured value was ompared to the alulated one from Eq. S. (Supporting Information S3) Figure S3. (a) Ciruit model for the experimental setup and (b) the equivalent iruit model replaing the soure meter (V out ) and the eletrode (V redox ) with the eletrial load (R load ). S6

7 V o satisfies the following equation: V o t RT 1 ln zf, (S3) where t is the transferene number for the ation. From Eqs. S3 and S4, t is given by t 1 V V o redox 1. (S4) The transferene number represents the ratio of the ation flux to the entire ion flux, i.e. t J /( J J ). ere, J and J are the ation and anion fluxes, respetively. Note that t 1 and t 0 indiate either entirely ation or anion seletive nanopores, respetively, while 0. 5 t means non ion-seletive nanopores if. If the energy harvesting system is omposed of entirely D D ation-seletive nanopores, i.e. t 1, then Vo Vredox and Vo beomes the maximum. Furthermore, if the soure meter (V out ) and the eletrode (V redox ) are regarded as the eletrial load (R load ) for the energy harvesting system as shown in Fig. S3 (b), R load is defined as follows: R load V out V I redox V I. (S5) The power, P, is therefore given by P VI V o R R R load load. (S6) The maximum power, P max, is obtained at R load R. Therefore, P max is given by P max Vo. (S7) 4R When P P max, V V o. The energy onversion effiieny, η, is defined as the ratio of the eletrial output energy to the input energy, and given by S S7

8 RT ln VI J J da. (S8) From Eqs. S1 and S3, the maximum energy onversion effiieny, η max, is given by max zf t J 1 I J. (S9) da Beause the ioni urrent passing through nanopores is defined as be given by I zf J J da, η max an also 1 t max 1. (S) S8

9 S3. easurement of redox potential differene To alibrate the eletrodes, the measured V redox using an eletrohemial ell system was ompared to the alulated value of Eq. S. Ativity oeffiients in Eq. S were alulated with the Pitzer model (Supporting Information S4). In the measurement of V redox, qualitative filter papers (ADVANTEC No.1 type, Toyo Roshi Kaisha, td., Japan) were used as the salt bridge. The filter papers are 00 µm thik and retain oarse and gelatinous preipitates µm in size. ere, the measured eletri potential between two Ag/AgCl eletrodes was attributed only to the asymmetri redox reations at the eletrode-solution interfae. Fig. S4 shows the measured and alulated V redox as a funtion of log( / ). The measured and alulated V redox were lose to eah other but the measured V redox was slightly smaller than the alulated one. The measured and alulated V redox of three kinds of eletrolytes KCl, NaCl and icl are summarized in Table S1. Figure S4. easured and alulated V redox as a funtion of log( / ) for three kinds of eletrolytes, (a) KCl, (b) NaCl, and () icl. The solid lines represent the fitting lines. S9

10 Table S1. easured and alulated V redox for the three eletrolytes: KCl, NaCl, and icl. (a) KCl 4 [] [] Calulated V redox [mv] easured V redox [mv] (b) NaCl 4 [] [] Calulated V redox [mv] easured V redox [mv] () icl 4 [] [] Calulated V redox [mv] easured V redox [mv] S

11 S4. Ativity oeffiients for alulating the redox potentials When the onentration of aqueous solutions is less than m, the ativity oeffiients are approximated by the Debye-ükel limiting law: S3 log i Az i I. (S11) ere, and z are the ativity oeffiient and valene of ion speies i, A is a onstant whih depends i i on temperature and an experimental value of water = mol -1/ kg 1/ at 98 K, and I is the ioni 1 strength for eletrolytes defined by I i zi, where i is the molar onentration of ion speies i. i owever, in this study, the onentration ranges from 0.1 m to 1, thus the Debye- ükel limiting law is not appliable and the Pitzer model is used instead to determine the ativity oeffiients in the high ioni strength solutions ( 1 ). In the Pitzer model, the ativity oeffiients of aqueous solutions at 98 K are given by the following equations: S4-S6 ln z f G G, (S1) ln z f G G, (S13) where the subsript and refer to ations and anions, respetively, and f is the eletrostati term. At a fixed valene, f is the same for all kinds of ions, and given by I f A ln 1 b 1 b I b I, (S14) where b is a onstant and assumed to be 1. and funtion, and given by A is the Debye-ükel oeffiient for the osmoti A N A 3 1 w 3 e kbt 3, (S15) S11

12 where N is the Avogardo number, and are the density and the dieletri onstant of pure A w solvent, kb is the Boltzmann onstant, and e is the eletri harge. The parameters G, G and in Eqs. S11 and S1 are given by G G B 1 i i z i C, (S16) G z B z C, (S17) G z B z C, (S18) where C is given by C C z z. (S19) For 1:1 eletrolyte, the parameters of B and B are given by B (0) (1) I 1 1 I exp I, (S0) B (1) I I exp I I, (S1) (0) (1) where is a onstant and assumed to be.0. The interation parameters of, and are summarized in Table S. C C (0) Table S. The interation parameters of, and for KCl, NaCl and icl eletrolytes. S6 Eletrolyte C (1) (0) (1) KCl NaCl icl S1

13 Fig. S5 shows the ativity oeffiients for three kinds of eletrolytes: KCl, NaCl and icl alulated by the Pitzer model. The alulated values of the ativity oeffiients are summarized in Table S3. Figure S5. Ativity oeffiients with respet to the onentrations for the three eletrolytes: KCl, NaCl, and icl. Table S3. Calulated values of the ativity oeffiients. Conentration [] KCl NaCl icl S13

14 S5. Effet of weak ion onentration solutions on p max and η max Fig. S6 shows the p max and η max with respet to log( / ) for KCl. The higher onentration ( ) was fixed at 0 m and the lower onentration ( ) gradually inreased from 0.3 to 30 m. The lower onentration ( ) was the variable in this experiment. The measured and alulated V redox values with respet to / are summarized in Table S4. In omparing Fig. S6 to Fig. 8 () and (d), the highest values of p max and η max derease with inreasing from 0.1 m, but both values of p max and η max retain simultaneously high levels at log( / ) = The highest p max is.85 W m - at log( / ) =.5 and the highest η max is 36.% at log( / ) = 1.5. Figure S6. Power density and energy onversion effiieny with respet to different onentration gradients for KCl. The error bars represent the standard deviations. S14

15 Table S4. easured and alulated V redox of KCl. 1 [] [] Calulated V redox [mv] easured V redox [mv] Referenes S1 A. J. Bard and. R. Faulkner, Eletrohemial ethods: Fundamentals and Appliations, John Wiley, New York, 001 S J. C. Fair and J. F. Osterle, J. Chem. Phys., 1971, 54, S3 P. Debye and E. ükel, Physikalishe Zeitshrift, 193, 4, 185. S4 B. S. Krumgalz and F. J. illero, ar. Chem., 198, 11, 09. S5 K. S. Pitzer, J. Phys. Chem., 1973, 77, 68. S6 K. S. Pitzer and G. ayorga, J. Phys. Chem., 1973, 77, 300. S15