Supplementary Materials for

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1 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 This PDF file includes: *Corresponding author. zhouyh@mail.ipc.ac.cn (Y.Z.); jiangzhenhua@jlu.edu.cn (Z.J.) Published 26 October 2018, Sci. Adv. 4, eaau1665 (2018) DOI: /sciadv.aau1665 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. 1 H NMR spectra (500 MHz, CDCl 3, room temperature) of monomer. Fig. S3. 1 H NMR spectra (500 MHz, DMSO-d 6, room temperature) of PAEK-HS15. Fig. S4. 1 H NMR spectra (500 MHz, DMSO-d 6, room temperature) of monomer. Fig. S5. 1 H NMR spectra (500 MHz, DMSO-d 6, room temperature) of PES-Py.

2 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. V open and I short 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, E Redox, and E Diff of HS10, HS15, and HS20. References (39, 40)

3 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.

4 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 (BBr 3 ), 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 (K 2 CO 3) was dried at 120 o C 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).

5 Section S3. Measurements 1 H NMR experiments were conducted using a Bruker 510 spectrometer (500 MHz for 1 H) with CDCl 3 or DMSO-d 6 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 25 o C. 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).

6 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), K 2 CO 3 (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 85 o C 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 ( g, mmol), 4,40-difluorobenzophenone ( g, mmol), 4,4 -(hexafluoroisopropylidene) diphenol ( g, 3.84 mmol), K 2 CO 3 ( g,

7 4.224 mmol), sulfolane (5.88 ml), and toluene (4 ml). The reaction mixture was refluxed for 3 h at o C. After the produced water was azeotroped off with toluene, the mixture was heated at 210 o C 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 o C 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 o C. 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 o C for 12 h to obtain PAEK-HS15. Scheme S1. Synthesis of PAEK-HS.

8 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: g 1-Bromo-2,5-dimethoxybenzene, 9.22 g 4-pyridylboronic acid and 20 g K 2 CO 3. A mixed liquor of 120 ml 1,4-dioxane and 60 ml H 2 O 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 BBr 3, 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 CH 2 Cl 2 completely, the reaction mixture was kept in an ice water bath. And then 8 ml BBr 3, which was dissolved in 15 ml CH 2 Cl 2, was dropwise added into the stirred mixture at 0 o C and stirred for 12 h at room temperature. Second, the mixture was cooled to 0 o C again and 20 ml ice-water was dropwise added to hydrolyze any excess BBr 3. Under stirring 2 h later, plenty of

9 20% sodium hydroxide was added until dissolved. Solvent CH 2 Cl 2 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 60 o C 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 K 2 CO 3 (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 150 o C for 3 h until the water was removed by azeotropic distillation with toluene. After the toluene was removed completely, the mixture was heated at 210 o C 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 80 o C for 20 h. Pure polymer (4 g) was obtained (yield 90%). Scheme S2. Synthesis of PES-Py.

10 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 1 H NMR spectroscopy with Chloroform-d (CDCl 3 ) as the solvent. The result was sufficiently consistent with the assigned structure of the monomer. The three signal peaks at ppm were assigned to aliphatic protons, and multiples signal at ppm were assigned to aromatic protons. The appearance of the peak in the range of ppm and 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 ppm. The clean spectrum confirmed that the monomer was successfully synthesized with a high purity. Fig. S2. 1 H NMR spectra (500 MHz, CDCl 3, room temperature) of monomer. 1 H NMR (500 MHz, CDCl3, r.t.): δ (m, 2H), (t, J = 8.1 Hz, 2H), (t, J = 6 Hz, 2H), (d, J = 7.8 Hz, 2H), (m, 27H), (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).

11 Characterization of PAEK-HS fig. S3 showed the 1 H NMR spectra of PAEK-HS15. The signals between 7.7 and 8.0 ppm were assigned to protons (a 1-4 ) due to electron-withdrawing groups (-SO 3 H 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. 1 H NMR spectra (500 MHz, DMSO-d 6, room temperature) of PAEK-HS15.

12 Section S7. Characterization of PES-Py Characterization of monomer The chemical structure was identified via 1 H-NMR with DMSO-d 6 as the solvent. The internal reference was tetramethylsilane (TMS). As can be seen in fig. S3, the characteristic signal of the methoxyl group (Ar-OCH 3 ) 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. 1 H NMR spectra (500 MHz, DMSO-d 6, room temperature) of monomer. Py-OMe 1 H NMR (500 MHz, DMSO-d 6, r.t.) δ 8.60 (dd, J = 4.5, 1.6 Hz, 2H), 7.53 (dd, J = 4.4, 1.6 Hz, 2H), (m, 3H), 3.75 (d, J = 6.9 Hz, 6H).

13 Py-OH 1 H NMR (500 MHz, DMSO-d 6, 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 1 H-NMR with DMSO-d 6 as the solvent. All signals were well assigned. PES-Py 1 H NMR (500 MHz, DMSO-d 6, r.t.) δ 8.49 (s, 2H), (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. 1 H NMR spectra (500 MHz, DMSO-d 6, 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

14 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)

15 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).

16 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.

17 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.

18 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 H 2 SO 4 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 o C for 12 h. the IEC values (meq g -1 ) were calculated from the titration results as follows IEC = C NaOHV NaOH W dry where V NaOH (ml) is the consumed volume of NaOH, C NaOH (mol L -1 ) is molarity of NaOH and W dry (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.

19 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/m 2, 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/m 2. 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.

20 The PNP equations are described as follows : (1) Ionic charge distribution in the liquid inside the nanochannels is obtained by Poission-Boltzman equation (2) Steady-state Nernst-Plank equation for ion motion 2 φ = F i z ic i (1) ε r j i = D i ( c i + z ifc i φ) (2) RT j i = 0 (3) Where φ is the electrical potential, F is Faraday constant, ε r is permittivity of the fluid, c i is the concentration of the ith ionic species, and z i is the valence. j i, D i are the ionic flux density, and diffusivity respectively. The diffusivity coefficients for cations and anions are both m 2 /s (KCl electrolyte is used for simplicity). The boundary condition of potential on the channel is n 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 Then, the ionic current can be calculated by n j = 0 (4) F I i = j i ds = D( c i + z i c i φ)ds (5) RT For the energy conversion simulation, a concentration gradient is applied and there is no external potential. The corresponding diffusion current can be calculated I osmotic = I n + I p (6)

21 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 C/m 2, C/m 2 ; C/m 2, 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.

22 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.

23 Section S15. The effect of the concentration gradients on short-circuit current and open-circuit voltage Fig. S13. V open and I short 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 V open and I short show dramatic increase as well.

24 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 t n is calculated following the equation E diff t n = 1 2 ( RT zf ln γ C H c + 1) H γ CL c L Where t n is the anion transference number; E diff 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).

25 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 (η max ) can be calculated as η max = (2t n 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. C Py (M) C HS (M) E diff (mv) t n η (%)

26 Power density (W/m 2 ) Current density (A/m 2 ) 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 CHCl 3 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 2.0 ph = Load resistance (k ) 0 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.

27 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.

28 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 (V open ) is contributed by the redox potential (E Redox ) on the electrode and the diffusion potential (E Diff ) from the Janus membrane. The equivalent circuit of the testing system is as shown as follow. R m represents internal resistance of the Janus membrane. Fig. S17. The equivalent circuit diagram of the testing system. Only the E Diff is contributed by the membrane. Obviously, the diffusion potential can be calculated as E Diff = V open - E Redox. An experimental method was used to subtract the contribution of the E Redox. 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 E Redox. This method could largely preclude the influence bought by other unexpected factors. The obtained V open, E Redox, and E Diff are shown in Table S3. Table S3. V, E Redox, and E Diff of HS10, HS15, and HS20. Concentration gradient(m/m) 10-5 / / / / /1 0.01/0.5 E Redox (mv) HS10 V open (mv) / E Diff (mv) / HS15 V open (mv) / E Diff (mv) / HS20 V open (mv) E Diff (mv)