advances.sciencemag.org/cgi/content/full/4/10/eaau1665/DC1

Supplementary Materials for

Unique ion rectification in hypersaline environment: A high-performance and

sustainable power generator system

Xuanbo Zhu, Junran Hao, Bin Bao, Yahong Zhou*, Haibo Zhang, Jinhui Pang, Zhenhua Jiang*, Lei Jiang

*Corresponding author. Email: zhouyh@mail.ipc.ac.cn (Y.Z.); jiangzhenhua@jlu.edu.cn (Z.J.)

Published 26 October 2018, Sci. Adv. 4, eaau1665 (2018)

DOI: 10.1126/sciadv.aau1665

This PDF file includes:

Section S1. The optical photograph of the Janus nanoporous membrane Section S2. Materials Section S3. Measurements Section S4. Synthesis of PAEK-HS Section S5. Synthesis of PES-Py Section S6. Characterization of PAEK-HS Section S7. Characterization of PES-Py Section S8. Inherent viscosity of the copolymers Section S9. FT-IR spectra of PAEK-HS Section S10. Porosity and pore size distribution Section S11. Zeta potential of PAEK-HS Section S12. Ion exchange capacity Section S13. Model building Section S14. Experimental setup Section S15. The effect of the concentration gradients on short-circuit current and open-circuit voltage Section S16. Ion selectivity of the membrane Section S17. Energy conversion efficiency Section S18. Fabrication of Janus heterogeneous membrane Section S19. The performance of the membrane under neutral Section S20. Tandem membrane-based power electronic devices Section S21. Electrode calibration Fig. S1. Digital photo of the large-scale Janus nanoporous membrane with an approximate thickness of 11 μm. Fig. S2. 1H NMR spectra (500 MHz, CDCl3, room temperature) of monomer. Fig. S3. 1H NMR spectra (500 MHz, DMSO-d6, room temperature) of PAEK-HS15. Fig. S4. 1H NMR spectra (500 MHz, DMSO-d6, room temperature) of monomer. Fig. S5. 1H NMR spectra (500 MHz, DMSO-d6, room temperature) of PES-Py.

Fig. S6. FT-IR spectra of PAEK-HP and PAEK-HS with different proportions of hydrophilic high concentration of sulfonated side chain (from top to bottom: 10, 15, and 20%, respectively). Fig. S7. The histogram of pore size distribution with Gaussian fit. Fig. S8. The zeta potential of membranes PAEK-HS10, PAEK-HS15, and PAEK-HS20. Fig. S9. The ion exchange capacity values of the sulfonated membranes. Fig. S10. Numerical simulation model based on PNP theory. Fig. S11. Numerical simulation results of the effect of the surface charge density on the ICR ratio. Fig. S12. Schematic of the electrochemical testing setup. Fig. S13. Vopen and Ishort of HS10, HS15, and HS20 under various concentration gradients (KCl). Fig. S14. Visual experiment for the selectivity. Fig. S15. The output power and current density of PES-Py/HS20 under a series of external load resistance at pH 7.4. Fig. S16. I-V curves of the 10 units’ device under river water (0.01 M NaCl) on the HS side and seawater (0.5 M NaCl) on the Py side. Fig. S17. The equivalent circuit diagram of the testing system. Scheme S1. Synthesis of PAEK-HS. Scheme S2. Synthesis of PES-Py. Table S1. Inherent viscosity of the copolymers. Table S2. The conversion efficiency of the Janus membrane at different salinity gradients. Table S3. V, ERedox, and EDiff of HS10, HS15, and HS20. References (39, 40)

Section S1. The optical photograph of the Janus nanoporous membrane

Fig. S1. Digital photo of the large-scale Janus nanoporous membrane with an

approximate thickness of 11 μm.

Section S2. Materials

Phenyl acetylene, piodoanisole, 2, 6-difluorobenzoic acid,

tetraphenylcyclopentadienone and 3-phenylpropyl bromide were purchased from

Sigma-Aldrich chemical corporation. 4, 4’-Difluorobenzophenone (DFB) and 4,

4’-(hexauoroisopropylidene) diphenol (6FBPA) were purchase from TCI chemical

company. 4,4'-difluorodiphenyl sulfone, 4-pyridylboronic acid,

1-bromo-2,5-dimethoxybenzene, borontribromide (BBr3), phosphotungstic acid

(PTA), tetrakis(triphenylphosphine)palladium (0), 4,4'-biphenol and N,

N-Dimethylacetamide (DMAc) were all supplied by Energy Chemical (Shanghai,

China). Tetramethylene sulfone (TMS) was purchased from Aladin Ltd. (Shanghai,

China). The above-mentioned reagents were used as received without any further

purification.

Other organic solvents, catalysts and reagents were obtained from Beijing Chemical

Reagent Company and were purified by standard methods. Of these, the TMS is

chemically pure, the other reagents are at least analytical grade. Anhydrous potassium

carbonate (K2CO3) was dried at 120oC for 24h before polymerization. High purity

water with a resistivity of 18.2 MΩ cm-1

was obtained from the Milli-Q purification

system (Millipore, Billerica, MA, USA).

Section S3. Measurements

1H NMR experiments were conducted using a Bruker 510 spectrometer (500 MHz for

1H) with CDCl3 or DMSO-d6 as the solvent. The internal reference was

tetramethylsilane (TMS).Fourier transform infrared (FTIR) spectra were measured on

a Bruker Vector 22 FT-IR spectrometer. Using an Ubbelohde viscometer, the inherent

viscosity of polymer was measured, with 0.1 g samples dissolved in 20 mL of DMAc

at 25oC. The ionic current through the membrane was measured by a Keithley 6487

picoammeter (Keithley Instruments, Cleveland, OH). The cross section images of the

sample were obtained with a field-emission scanning electron microscope (S-4800,

Japan). The pore structure of the copolymers was investigated by transmission

electron microscope (JEM 1200 EX; Jeol, Japan). Diluted polymer solutions were cast

on an ultrathin-carbon-coated copper grid. Selective staining of the pyridine was

accomplished by exposure of the thin sections to phosphotungstic acid solution. The

fluorescently images that the permeation of fluorescent dyes through the membrane

from the perpendicular direction were obtained using a Nikon C2 confocal laser

scanning microscope (Nikon Corp., Tokyo, Japan). Small angle X-ray scattering

(SAXS, Rigaku D/max-2550) was measured for membranes at 50% RH and room

temperature. Thermogravimetric analysis (TGA) was employed to assess thermal

stability of membranes with Pyris 1 TGA (Perkine Elmer) under a nitrogen

atmosphere. The mechanical properties of membranes were measured at room

temperature on SHIMADZU AG-I 1 KN at a strain rate of 2 mm min-1

. The wet

membrane samples were obtained by immersing in water for at least 48 h. Zeta

potential was measured by the SurPASS Electro-kinetic Analyzer (Anton-Paar).

Section S4. Synthesis of PAEK-HS

Monomer

The synthetic steps of this monomer can be described as followed.

(4-(3-Bromopropyl)phenyl)(2, 6-difluorophenyl)methanone and

1-(4-hydroxyphenyl)-2,3,4,5,6-pentaphenylbenzene were synthesized according to a

procedure previously reported.

(2, 6-Diflouorophenyl)(4-(3-(4-(1, 2, 3, 4, 5-pentaphenylphenoxy)) propyl)phenyl)

methanone:

(4-(3-Bromopropyl)phenyl)(2,6-difluorophenyl)methanone (2.97 g, 8.76 mmol),

1-(4-hydroxyphenyl)-2,3,4,5,6-pentaphenylbenzene (4.00 g, 7.3 mmol), K2CO3 (1.21

g, 8.76 mmol) and 100 mL of N,Ndimethylformamide (DMF) were charged into a

250 mL threenecked round-bottomed flask, fitted with a condenser, an argon

inlet/outlet, and a magnetic stirrer. The mixture was kept at 85oC for 8 h under argon

protection. The resulting mixture was cooled, and then poured into water (400 mL) to

precipitate a white powder, which was collected by filtration. The crude product was

purified by ethanol/chloroform (3:1) recrystallization, and further purified by column

chromatography isolation with Chloroform to give 4.8 g of monomer (yield 81%).

PAEK-HS

A typical polycondensation procedure, illustrated by preparation of the poly(aryl ether

ketone)s with hexaphenylbenzene (PAEK-HP15) copolymer (where 15 is the molar

percentage of monomer

(2,6-Diflouorophenyl)(4-(3-(4-(1,2,3,4,5-pentaphenylphenoxy)) propyl)phenyl)

methanone in the total difluoride monomer), can be described as follows (Scheme S1).

To a 25 mL three-necked roundbottomed flask, fitted with a DeaneStark trap, a

condenser, a nitrogen inlet/outlet, and a magnetic stirrer, were charged, monomer 3

(0.4659 g, 0.576 mmol), 4,40-difluorobenzophenone (0.7122 g, 3.264 mmol),

4,4’-(hexafluoroisopropylidene) diphenol (1.2911 g, 3.84 mmol), K2CO3 (0.5938 g,

4.224 mmol), sulfolane (5.88 mL), and toluene (4 mL). The reaction mixture was

refluxed for 3 h at 170-180 oC. After the produced water was azeotroped off with

toluene, the mixture was heated at 210 oC for about 6 h until a highly viscous solution

was obtained. Then the resulting mixture was cooled, poured into water (400 mL) to

precipitate a white fibrous polymer. The resulting polymer was filtered and washed

with hot water and hot ethanol. After the polymer was dried in vacuo at 120 oC for 12

h. 0.9 g of PAEK-HP15 was charged into a 250 mL round-bottomed flask equipped

with a dropping funnel. Then, dry dichloromethane (30 mL) was added to the flask,

and the mixture was cooled to 0 oC. To the mixture was added dropwise a solution of

chlorosulfonic acid (0.5 mL, 2.5 mmol) in dry dichloromethane (30 mL) and

vigorously stirred at room temperature for 8 h. Chlorosulfonic acid was calculated to

be present in fourfold excess with respect to the hexaphenylbenzene unit of the

copolymer. The resulting polymer was washed with 10% KOH aqueous solution and

then deionized water till neutral. The polymer was dried in vacuo at 120 oC for 12 h to

obtain PAEK-HS15.

Scheme S1. Synthesis of PAEK-HS.

Section S5. Synthesis of PES-Py

Monomer

As shown in Scheme S2, the charged monomer was synthesized via the well-known

reaction, Suzuki cross-coupling as follows.

Step 1:

The following reagents and solvent were put into a 250 mL round-bottom flask

equipped with a stirring bar and a condenser: 10.85 g 1-Bromo-2,5-dimethoxybenzene,

9.22 g 4-pyridylboronic acid and 20 g K2CO3. A mixed liquor of 120 mL 1,4-dioxane

and 60 mL H2O is used as solvent. Subsequently, the mixed reagents and solvent were

degassed by the Schlenk Line with argon atmosphere. And then

tetrakis(triphenylphosphine)palladium (0) (1.73 g) was added while the whole system

was being purged in argon atmosphere. After the materials as prepared, the flask was

heated up to 90℃ for 24 h with the agitation on. The proceeding degree of the

reaction was ascertained with TLC (Thin-Layer Chromatography). At last, the

reaction solution was cooled to room temperature, and a Rotary Evaporators removed

the solvent. Purification was achieved by flash chromatography

(tetrahydrofuran/petroleum ether) on silica gel. Catalyst can be removed

simultaneously. Then our goal monomer 2-(pyridin-4-yl)-1, 4-dimethoxybenzene

(Py-OMe) was obtained (9.68g, yield 90%).

Step 2:

By using a dichloromethane solution of BBr3, dimethoxybenzene was demethylated to

acquire the bisphenol monomer (Py-OH).

First, 4 g Py-OMe was added to a 250 mL three-necked flask under the protection of

nitrogen. After it was dissolved in 40 mL CH2Cl2 completely, the reaction mixture

was kept in an ice water bath. And then 8 mL BBr3, which was dissolved in 15 mL

CH2Cl2, was dropwise added into the stirred mixture at 0oC and stirred for 12 h at

room temperature. Second, the mixture was cooled to 0oC again and 20 mL ice-water

was dropwise added to hydrolyze any excess BBr3. Under stirring 2 h later, plenty of

20% sodium hydroxide was added until dissolved. Solvent CH2Cl2 was removed by

reduced pressure distillation. In the end, via to adjust the pH value of the remaining

liquid by hydrochloric acid to 6, white powder was separated out. After washed with

water three times, the monomer, 2-(pyridin-4-yl)-1, 4-benzenediol (Py-OH), was

acquired after being dried in a vacuum oven at 60oC for 24 hours.

PES-Py

A 100mL three-necked round-bottom flask equipped with a mechanical stirrer, a

nitrogen inlet with a thermometer, and a Dean–Stark trap with a condenser, was

charged with Py-OH (1.87 g), 4, 4'-fluorodiphenyl sulfone (2.54 g), anhydrous K2CO3

(1.5 g), tetramethylene sulfone (20 mL) and toluene (15 mL). The mixture was stirred

at room temperature for 10 min under argon atmosphere, and then heated at 150oC for

3 h until the water was removed by azeotropic distillation with toluene. After the

toluene was removed completely, the mixture was heated at 210oC for 6 h. As the

polymerization was completed, the viscous solution was poured into water. A blender

was used to pulverize the flexible threadlike polymer. After being washed with hot

deionized water and ethanol several times and dried under vacuum at 80oC for 20 h.

Pure polymer (4 g) was obtained (yield 90%).

Scheme S2. Synthesis of PES-Py.

Section S6. Characterization of PAEK-HS

Characterization of monomer

As shown, the monomer containing flexible and highly concentrated sulfonation sites

was easily synthesized by Williamson reaction to afford a high yield. The structure of

the monomer was confirmed by 1H NMR spectroscopy with Chloroform-d (CDCl3) as

the solvent. The result was sufficiently consistent with the assigned structure of the

monomer. The three signal peaks at 1.9-3.9 ppm were assigned to aliphatic protons,

and multiples signal at 6.7-7.8 ppm were assigned to aromatic protons. The

appearance of the peak in the range of 7.39-7.49 ppm and 6.98-7.03 ppm were

assigned to the proton on the benzene ring with fluorine atom and carbonyl. And the

protons on the hexaphenylbenzene were appeared in the range of 6.7-6.87 ppm. The

clean spectrum confirmed that the monomer was successfully synthesized with a high

purity.

Fig. S2. 1H NMR spectra (500 MHz, CDCl3, room temperature) of monomer.

1H

NMR (500 MHz, CDCl3, r.t.): δ 1.93-2.03 (m, 2H), 2.76-2.81 (t, J = 8.1 Hz, 2H),

3.74-3.78 (t, J = 6 Hz, 2H), 6.37-6.4 (d, J = 7.8 Hz, 2H), 6.7-6.87 (m, 27H), 6.98-7.03

(t, J = 7.8 Hz, 2H), 7.22e7.25 (d, J = 8.4 Hz, 2H), 7.39e7.49 (m, 1H), 7.75e7.78 (d, J

= 8.4 Hz, 2H).

Characterization of PAEK-HS

fig. S3 showed the 1H NMR spectra of PAEK-HS15. The signals between 7.7 and 8.0

ppm were assigned to protons (a1-4) due to electron-withdrawing groups (-SO3H or

-C=O) present in their neighborhood. Moreover, the chemical shift of the protons on

the hexaphenylbenzenedisappeared or shifted to lower magnetic fields. The clear

signals at 4.7 ppm were assigned to protons of sulfonic acid, while the signals of 2.5

ppm were assigned to DMSO-d6. All peaks of spectral line were assigned to

reasonable attribution. This confirm that the postsulfonation proceeded successfully as

we expected.

Fig. S3.

1H NMR spectra (500 MHz, DMSO-d6, room temperature) of

PAEK-HS15.

Section S7. Characterization of PES-Py

Characterization of monomer

The chemical structure was identified via 1H-NMR with DMSO-d6 as the solvent. The

internal reference was tetramethylsilane (TMS). As can be seen in fig. S3, the

characteristic signal of the methoxyl group (Ar-OCH3) was observed at approximately

3.75 ppm. After demethylation, this signal (3.75 ppm) disappeared, and two new

singlets at approximately 8.91 and 9.12 ppm appeared, corresponding to the hydroxyl

on the aromatic ring (Ar-OH). The results demonstrated that methyl had been taken

off completely. Also, the proton signal of the aromatic ring (from 6.94 to 7.14) moved

to high field (from 6.64 to 6.82) as a result of the powerful electron-donating effect by

hydroxyl groups. The signals of hydrogen in pyridine ring pendants were observed at

about 8.55 and 7.54 ppm respectively. All signals were well assigned as shown in fig.

S4. These results proved that the synthesis of Py-OH was successful.

Fig. S4. 1H NMR spectra (500 MHz, DMSO-d6, room temperature) of monomer.

Py-OMe

1H NMR (500 MHz, DMSO-d6, r.t.) δ 8.60 (dd, J = 4.5, 1.6 Hz, 2H), 7.53 (dd, J = 4.4,

1.6 Hz, 2H), 7.16 – 6.91 (m, 3H), 3.75 (d, J = 6.9 Hz, 6H).

Py-OH

1H NMR (500 MHz, DMSO-d6, r.t.) δ 9.12 (s, 1H), 8.91 (s, 1H), 8.55 (dd, J = 4.5, 1.6

Hz, 2H), 7.54 (dd, J = 4.5, 1.6 Hz, 2H), 6.72 (ddd, J = 13.0, 11.6, 5.8 Hz, 3H).

Characterization of PES-Py

As shown in (fig. S5), the chemical structure of PES-Py was identified via 1H-NMR

with DMSO-d6 as the solvent. All signals were well assigned.

PES-Py

1H NMR (500 MHz, DMSO-d6, r.t.) δ 8.49 (s, 2H), 8.03 - 7.72 (m, 4H), 7.44 (d, J =

4.8 Hz, 3H), 7.27 (s, 2H), 7.14 (dd, J = 39.2, 5.6 Hz, 4H).

Fig. S5. 1H NMR spectra (500 MHz, DMSO-d6, room temperature) of PES-Py.

The integral ratio of the proton signal in the pyridine pendants around nitrogen at 8.5

ppm (signal a) and the proton signal in the aromatic ring around sulfone between 8.05

to 7.75 ppm (signal b) is 1/2. On the basis of these, the molar percentage of the

pyridine group pendants in PES-Py were calculated by 2a/b to be 100%. This proved

that the PES-Py synthesized successfully

Section S8. Inherent viscosity of the copolymers

The inherent viscosities of the obtained copolymers were determined using an

Ubbelohde viscometer in a thermostatic container at 25 ˚C. Each 0.1 g copolymer

sample was dissolved in 20 mL of DMAc. As can be seen in Table S1, high molecular

weight of all polymers were synthesized successfully. The inherent viscosities of

sulfonated copolymers have no significant difference and are all in the higher range,

which is attributed to their strong intermolecular force.

Table S1. Inherent viscosity of the copolymers.

PES-Py HS10 HS15 HS20

Inherent viscosity（dL/g） 0.56 0.71 0.68 0.75

Section S9. FT-IR spectra of PAEK-HS

Fourier transform infrared (FT-IR) spectra were measured on a Bruker Vector 22

FT-IR spectrometer. The polymer solution was coated on the Potassium bromide flake

and dried completely before testing. The stretching vibration of the C=O groups of

PAEK-HP and PAEK- HS can be seen at 1658 cm-1

. In comparison with PAEK-HS

copolymer the characteristic absorption of the sulfonic acid group was observed at

1039 cm-1

and 671 cm-1

for all sulfonated polymers. These results confirmed the

successful introduction of the sulfonic acid groups onto the polymer side chains.

Fig. S6. FT-IR spectra of PAEK-HP and PAEK-HS with different proportions of

hydrophilic high concentration of sulfonated side chain (from top to bottom: 10,

15, and 20%, respectively).

Section S10. Porosity and pore size distribution

According to the TEM images of PAEK-HS, porosity analyses were performed using

Image J software. The pore size distribution of with Gaussian fit were as shown in fig.

S7.

Fig. S7. The histogram of pore size distribution with Gaussian fit. The image a b

and c are the pore size distribution of PAEK-HS10, PAEK-HS15 and PAEK-HS20,

respectively.

Section S11. Zeta potential of PAEK-HS

Fig. S8. The zeta potential of membranes PAEK-HS10, PAEK-HS15, and

PAEK-HS20. The surface charge density improves significantly with increasing

pendant proportion.

Section S12. Ion exchange capacity

The IEC values of the sulfonated membranes were measured by traditional acid-base

titration. The pure membranes have been completely dried and weighed before the

test. And put the membranes in 1.0 M H2SO4 solution for 24 h to protonize the

sulfonic groups and washed thoroughly with deionized water until neutral. Then the

protonated membranes were immersed in a 2.0 M solution of NaCl for 48 h to replace

the protons of sulfonic acid groups with sodium ions. The ion concentration of H+

represents the number of foundation sulfonic acid group of the membrane. The

solution was titrated using about 0.01 M NaOH solution, with phenolphthalein as

indicator. And the NaOH solution was calibrated by potassium hydrogen phthalate

which was dried under 105-110 oC for 12 h. the IEC values (meq g

-1) were calculated

from the titration results as follows

𝐼𝐸𝐶 =𝐶𝑁𝑎𝑂𝐻𝑉𝑁𝑎𝑂𝐻

𝑊𝑑𝑟𝑦

where VNaOH (mL) is the consumed volume of NaOH, CNaOH (mol L-1

) is molarity of

NaOH and Wdry (g) is the weight of dry membranes.

Fig. S9. The ion exchange capacity values of the sulfonated membranes. The

experimental IEC values of PAEK-HS were determined by titration, and were a little

different from calculated values. The reasons for this phenomenon might be

cross-linking effect of the chlorosulfonic acid during the process of sulfonation, which

gave rise to decline of the degree of the sulfonation. All in all, the experimental IEC

values of PAEK-HS were basically agreed well with calculated values.

Section S13. Model building

In the past few years, the ionic current rectification phenomena have been widely

reported in nanoscale pores or channels. In our system, the ionic current rectification

behavior is realized in the heterogeneous membrane with 3D porous networks. For the

3D porous model is too complicated to build, here for simplicity, we take the 1D

model to understand and quantitate the ion transport mechanism. For the convectional

ionomer membrane (ion exchange membrane), no ionic current rectification (ICR)

phenomena exists, indicating the 3D symmetry pore structure inside the membrane.

According to the phase-separation theory, charged hydrophilic groups tend to

self-assemble into well-defined mesoscopic-scale spheroidal 3D pores, while the

hydrophobic backbone aggregates as one phase. So here, the simple model is built

based on this, two cylindrical channels (positive charge density and negative surface

charge density) as shown in fig. S10.

The transmembrane ionic transport in our membrane is presumed to be governed by

the surface charge. For the PAEK-HS side, the surface charge density is estimated to

be 0.2 C/m2, connected pores are considered as a cylindrical shape with ca. 18 nm

pore size and 400 nm length; while the 3D connected PES-Py pores are posed as

cylindrical tube with ca. 8 nm pore size and 40 nm length. The surface charge density

of PES-Py side is estimated to be 0.05 C/m2. We hypothesize that our system could be

quantitatively explained by the Poisson and Nernst-Plank (PNP) equations with

proper boundary conditions.

The simulation temperature was 298 K. The dielectric constant of the aqueous

solution was assumed to be 80.

Fig. S10. Numerical simulation model based on PNP theory.

The PNP equations are described as follows39-40

:

(1) Ionic charge distribution in the liquid inside the nanochannels is obtained by Poission-Boltzman

equation

∇2𝜑 = −𝐹 ∑ 𝑧𝑖𝑐𝑖𝑖

𝜖𝑟 (1)

(2) Steady-state Nernst-Plank equation for ion motion

𝑗𝑖 = 𝐷𝑖(∇𝑐𝑖 +𝑧𝑖𝐹𝑐𝑖

𝑅𝑇∇𝜑) (2)

∇ ∙ 𝑗𝑖 = 0 (3)

Where 𝜑 is the electrical potential, F is Faraday constant, 𝜖𝑟 is permittivity of the

fluid, ci is the concentration of the ith ionic species, and zi is the valence. 𝑗𝑖, 𝐷𝑖 are

the ionic flux density, and diffusivity respectively. The diffusivity coefficients for

cations and anions are both 2.0×10-9

m2/s (KCl electrolyte is used for simplicity). The

boundary condition of potential on the channel is �⃗� ⋅ 𝜑∇ = −𝜎/𝜖, where 𝜎

represents the surface charge density.

On the reservoir wall, 𝜎=0. On the left walls, 𝜎 is the surface charge density of

PAEK-HS. On the right walls, 𝜎 is the surface charge density of PES-Py. The ion

flux has the zero normal components at boundaries

�⃗⃗� ∙ 𝑗 = 0 (4)

Then, the ionic current can be calculated by

𝐼𝑖 = ∬ 𝑗𝑖 𝑑𝑠 = −∬𝐷(∇𝑐𝑖 + 𝑧𝑖𝑐𝑖𝐹

𝑅𝑇∇𝜑)𝑑𝑠 (5)

For the energy conversion simulation, a concentration gradient is applied and there is

no external potential. The corresponding diffusion current can be calculated

𝐼𝑜𝑠𝑚𝑜𝑡𝑖𝑐 = 𝐼𝑛 + 𝐼𝑝 (6)

Fig. S11. Numerical simulation results of the effect of the surface charge density

on the ICR ratio. The length of the heterojunction is fixed while the surface charge

density varies 100 times. Here, the surface charges are set as -0.002 C/m2, 0.005 C/m

2;

-0.02 C/m2, 0.05 C/m

2; and -0.2 C/m

2, 0.05 C/m

2, respectively. Obviously, with

increasing surface charge density, the critical concentration peak (where highest

rectification ratio appears in various electrolyte concentration) shift from the low

concentration to high concentration. In our theoretical model, rectification ratio highly

depends on the surface charge density of the pores. The length of the heterojunction is

fixed while the surface charge density varies 100 times. The simulated results

demonstrate the peak of highest rectification ratios shift from low concentration to

high concentration with the increasing surface charge density.

Section S14. Experimental setup

The experimental setup was built as shown to study the power generation and ionic

transport property of the Janus membranes. The ionic current through the membrane

was measured by a Keithley 6487 picoammeter (Keithley Instruments, Cleveland,

OH).

The transmembrane potential was provided by a pair of Ag|AgCl electrodes with

equal electrolyte placed on the two sides of the membrane. Sweeping voltages from -2

V to 2 V was applied across the membrane. The membrane was fixed in the connector

of two compartment as a separator. Electrolyte solutions were prepared with

deionized water (18.2 MΩ∙cm, MilliQ).

Power electronic devices systems was built by series heterogeneous nanoporous

membranes with unequal electrolyte placed on the two sides of the membrane.

Fig. S12. Schematic of the electrochemical testing setup.

Section S15. The effect of the concentration gradients on short-circuit current

and open-circuit voltage

Fig. S13. Vopen and Ishort of HS10, HS15, and HS20 under various concentration

gradients (KCl). The concentrations of KCl solution on HS side was fixed at 10 μM,

the concentrations on Py side was increased from 100 μM to 1 M. As the concentration

gradient increases, both the Vopen and Ishort show dramatic increase as well.

Section S16. Ion selectivity of the membrane

The selectivity of the membrane is testified by a visual experiment. Two oppositely

charged fluorescent dyes (negatively charged sulfonated rhodamine, positively

charged propidium iodide) were to mark the membrane. A droplet of fluorescent dye

solution is added onto the membrane from only PES-Py side (same as preferential

direction). The confocal laser scanning microscope is used to image the permeation of

fluorescent dyes through the membrane at the other side. As shown in fig. S14, the

negatively charged dyes are permeable across the membrane easily, while the

positively charged dyes are excluded from the membrane.

Fig. S14. Visual experiment for the selectivity. The confocal laser scanning

microscope images of the polymer membrane with negatively charged fluorescent dye

(A) and positively charged fluorescent dye (B). Only the negatively charged dyes can

pass the membrane easily.

As can be seen, for our membrane, it behaves as an anion selector and the

transference number 𝑡𝑛 is calculated following the equation

𝑡𝑛 =1

2(

𝐸𝑑𝑖𝑓𝑓

𝑅𝑇𝑧𝐹

ln𝛾𝐶𝐻

𝑐𝐻

𝛾𝐶𝐿𝑐𝐿

+ 1)

Where 𝑡𝑛 is the anion transference number; 𝐸𝑑𝑖𝑓𝑓 refers to the diffusion potential;

R, T, z, F, refer to the gas constant, temperature, valence charge and Faraday constant

respectively; 𝛾 and 𝑐 refer to ion activity coefficient and concentration(Table S2).

Section S17. Energy conversion efficiency

Energy conversion efficiency is defined as the ratio of the output energy (electrical

energy) to the input energy (Gibbs free energy of mixing). For our anion-selective

system, maximum power generation (𝜂𝑚𝑎𝑥) can be calculated as

𝜂𝑚𝑎𝑥 =(2𝑡𝑛 − 1)2

2

The KCl concentration faces PAEK-HS side was fixed at 10 μM and varying the KCl

concentration faces PES-Py side from 100 μM to 1 M. The energy conversion

efficiency under a series of concentration gradient can be calculated. Clearly, the

conversion efficiency is much enhanced, especially in high salt concentration. Still,

the efficiency maintained up to 35.7% by mixing seawater and river water.

Table S2. The conversion efficiency of the Janus membrane at different salinity

gradients. The asymmetric solution are KCl solution except the seawater and river

water in the last row.

CPy (M) CHS (M) Ediff (mV) tn η (%)

10-4

10-5

40 0.838 22.9 10

-3 10

-5 85 0.859 25.8 10

-2 10

-5 159 0.948 40.1 10

-1 10

-5 201 0.925 36.1 1 10

-5 226 0.882 29.2 0.5 0.01 85 0.923 35.7

Section S18. Fabrication of Janus heterogeneous membrane

The sulfonated polymers were dissolved in DMAc. The membrane was prepared by

pouring sulfonated copolymer solutions onto leveled clean glass plates after filtration.

The removal of DMAc was accomplished by drying at 60℃ for 15 h and under

vacuum at 120℃ for 15 h. After cooling to room temperature, PES-Py solution in

CHCl3 was spin-coated on the as-prepared membrane and dried at 45℃ in a vacuum

oven for 12 h and peel off. The copolymer self-assembled into 3D porous membrane

via micro/nano-phase separation. Their thickness can be controlled by adjusting the

concentration of the polymer.

Section S19. The performance of the membrane under neutral

1 10 100 1000

0.0

0.5

1.0

1.5

2.0C

urr

en

t d

en

sit

y (

A/m

2)

Po

we

r d

en

sit

y (

W/m

2)

Load resistance (k)

0

20

40

60

pH = 7.4

Fig. S15. The output power and current density of PES-Py/HS20 under a series

of external load resistance at pH 7.4. As the load resistance gradually increases, the

current density is reduced, while the output power reaches a maximum at about 20k.

Section S20. Tandem membrane-based power electronic devices

Membranes are connected in series to build up voltage and we test the output voltage

from independent devices containing 1–10 units. River water (0.01 M NaCl) and

seawater (0.5 M NaCl) were mixed with the single-unit device. The output voltages

reach up to about 1.5 V and show a perfect linear relationship.

Fig. S16. I-V curves of the 10 units’ device under river water (0.01 M NaCl) on

the HS side and seawater (0.5 M NaCl) on the Py side. Multiple membrane-based

unit cells connected in series generate a voltage as high as about 1.5 V. The output

voltages show a perfect linear relationship of 150 mV per single unit cell under the

concentration gradient of 50.

Section S21. Electrode calibration

The energy conversion property was tested by measuring the scanning I−V cycles in

the presence of a concentration gradient across the membrane. The sweeping voltages

from -0.5 V to 0.5 V was applied with a step of 0.05 V. The intercept on the voltage

axis (Vopen) is contributed by the redox potential (ERedox) on the electrode and the

diffusion potential (EDiff) from the Janus membrane. The equivalent circuit of the

testing system is as shown as follow. Rm represents internal resistance of the Janus

membrane.

Fig. S17. The equivalent circuit diagram of the testing system. Only the EDiff is

contributed by the membrane. Obviously, the diffusion potential can be calculated as

EDiff = Vopen - ERedox. An experimental method was used to subtract the contribution of

the ERedox. In the same electrochemical experimental setup, the separator membrane

replaced by a nonselective silicon membrane containing a single micro-window in

which case the measured voltage was contributed solely by the ERedox. This method

could largely preclude the influence bought by other unexpected factors. The obtained

Vopen, ERedox, and EDiff are shown in Table S3.

Table S3. V, ERedox, and EDiff of HS10, HS15, and HS20.

Concentration gradient(M/M) 10-5

/10-4

10-5

/10-3

10-5

/10-2

10-5

/10-1

10-5

/1 0.01/0.5

ERedox (mV) 21 48 74 96 105 67

HS10 Vopen (mV) 36 123 215 261 275 /

EDiff (mV) 15 75 141 165 170 /

HS15 Vopen (mV) 23 126 217 282 311 /

EDiff (mV) 2 78 143 186 206 /

HS20 Vopen (mV) 61 131 233 296 331 152

EDiff (mV) 40 83 159 200 216 85