Aqueous-Processed, High-Capacity Electrodes

Transcription

1 S1 Aqueous-Processed, High-Capacity Electrodes for Membrane Capacitive Deionization Amit Jain 1,2, Jun Kim 2,3, Oluwaseye M Owoseni 2,5, Cierra Weathers 1,2, Daniel Caña 1,2, Kuichang Zuo 2,3, W. Shane Walker 2,5, Qilin Li 2,3, *, Rafael Verduzco 1,2,4, * 1 Department of Chemical and Biomolecular Engineering, Rice University, MS 362, 6100 Main Street, Houston, USA 2 NSF Nanosystems Engineering Research Center Nanotechnology-Enabled Water Treatment, Rice University, MS 6398, 6100 Main Street, Houston, USA 3 Civil and Environmental Engineering, Rice University, MS 319, 6100 Main Street, Houston, USA 4 Material Science and Nanoengineering, Rice University, MS 325, 6100 Main Street, Houston, USA 5 Civil Engineering, The University of Texas at El Paso, 500 W University Avenue, El Paso, Texas, USA Correspondence to: rafaelv@rice.edu, qilin.li@rice.edu Keywords: Capacitive Deionization, Membrane, Polymer, Activated Carbon, Desalination.

2 S2 Figure/Table Figure S1. Various steps involved in electrode preparation. Figure S2. Water contact angle analysis and electrochemical characterization of PVA and PVDF electrodes. Figure S3. FTIR spectra for free-standing ion-exchange polymer membranes and ion-exchange polymer-coated electrodes Figure S4. Effluent conductivity for graphite sheet device (no activated carbon or binder) with cation and anion-exchange polymer coatings Figure S5. Effluent conductivity for long-term (24 h) experiments Figure S6. Effluent ph for long-term (24 h) experiments Figure S7. Current supplied/discharged for long-term (24 h) experiments Figure S8. Performance comparison of PVA-PC-MCDI, PVA-MCDI1 (Membranes International Inc.) and PVA-MCDI2 (ASTOM-Neosepta) systems. Table S1. Membrane properties for two types of commercial Ionexchange membranes. Table S2. Mass and test conditions for each electrode. Table S3. Analysis of reproducibility through fabrication and testing of two separate samples using identical procedures and composition. Table S4. Analysis of performance degradation during operation through comparison of performance parameters for early operation cycles (6 th through 10 th cycles) compared with later cycles (36 th through 40 th ). Table S5. Analysis of performance comparison for various systems between 6th to 10th cycles and 36th to 40th cycles. Page S3 S4 S5 S6 S7 S8 S9 S10 S10 S11 S11 S12 S12

3 Figure S2. Various steps involved in electrode preparation. (a) Schematic for slurry preparation to fabricate electrodes (b) Photograph of equipment used to deposit slurry on the current collector. (c) photograph of an electrode coated partially (rectangular strips) with the ionexchange polymer. (d) photographs of 10 cm x 1cm electrodes and ion-exchange membranes. From left-to-right: bare electrode, polymer-coated electrode, commercial anion exchange membrane, and commercial cation exchange membrane. S3

4 S4 CV measurements: CV measurements were performed on the bare electrodes. 5mv/s scan rate, 1 M NaCl solution, 2 cm 2 cross-section area, Ag/AgCl as reference electrode and platinum wire as counter electrode. Specific capacitance was calculated as per the literature 40. From Figure S3d, specific capacitance is higher when PVA was used as a binder. Figure S2. Water contact angle analysis and electrochemical characterization of PVA and PVDF electrodes. (a) water contact angle on PVDF electrode (78 deg), (b) water contact angle on PVA electrode (20 deg) (c) current versus applied potential for both PVDF and PVA electrodes and (d) calculated specific capacitance for PVDF and PVA electrodes.

5 Figure S3. FTIR spectra for free-standing ion-exchange polymer membranes and ion-exchange polymer-coated electrodes. (a) bare PVA electrode (yellow), free-standing QPVA free-standing film (red), and QPVA-coated electrode (black), (b) bare PVA electrode (yellow), PVA/SSA freestanding film (green) and coated electrode (black). S5

6 S6 A control experiment using the graphite charge collector coated with ion-exchange membranes was conducted to evaluate the importance of the porous carbon electrode. As shown in Figure S7, a very small change in effluent conductivity is achieved during operation. For the sample shown above, roughly 0.04 mg salt was removed in one adsorption cycle compared with 2.65 mg of salt adsorbed by polymer coated electrodes. This demonstrates that the porous carbon electrodes are responsible for the vast majority of salt uptake. Figure S4. Effluent conductivity for graphite sheet device (no activated carbon or binder) with cation and anion-exchange polymer coatings.

7 Figure S5. Effluent conductivity for long-term (24 h) experiments with (a)pvdf-cdi, (b)pva- CDI, (c)pva-pc-mcdi, (d)pva-mcdi, and (e)pvdf-mcdi. S7

8 Figure S6. Effluent ph for long-term (24 h) experiments with (a)pvdf-cdi, (b)pva-cdi, (c)pva-pc-mcdi, (d)pva-mcdi, and (e)pvdf-mcdi. (f) effluent ph for 6 th through 10 th cycles of operation for PVDF-CDI, PVDF-MCDI and (g) effluent ph for 6 th through 10 th cycles of operation for PVA-CDI, PVA-PC-MCDI, and PVA-MCDI. S8

9 Figure S7. Current supplied/discharged for long-term (24 h) experiments with (a)pvdf-cdi, (b)pva-cdi, (c)pva-pc-mcdi, (d)pva-mcdi, and (e)pvdf-mcdi. (f) current for 6 th through 10 th cycles of operation for PVDF-CDI, PVDF-MCDI and (g) current for 6 th through 10 th cycles of operation for PVA-CDI, PVA-PC-MCDI, and PVA-MCDI. S9

10 S10 Figure S8. Performance comparison of PVA-PC-MCDI, PVA-MCDI1 (Membranes International Inc.) and PVA-MCDI2 (ASTOM-Neosepta) systems. (a) effluent conductivity over one cycle showing higher initial uptake for polymer-coated system, and (b) comparison of SAC and charge efficiencies indicating the further potential for the salt removal performance improvement for the polymer coated system. Table S1. Membrane properties for two types of commercial Ionexchange membranes. Membranes from Membranes International were used to perform the detailed comparison in this work and the membranes form Neosepta were used to showcase the further potential of higher adsorption capacity. Parameters Membranes International INC. ASTOM- Neosepta Membrane type CMI-7000S CMX Electrical resistance (Ω cm 2 ) < Wet thickness (µm) 500± Ion exchange capacity (meq/g) 1.6±0.1 NA Permselectivity 94 NA Cost ($/m 2 )

11 S11 Table S2. Mass and test conditions for each electrode. Sample Configuration Electrode weight (mg) Feed Conductivity (ms/cm) PVA - CDI PVDF - CDI PVA - PC - MCDI PVA - MCDI PVDF - MCDI Table S3 Analysis of reproducibility through fabrication and testing of two separate samples using identical procedures and composition. Sample # Combined weight of two electrodes (mg) Salt Adsorption Capacity (mg/g) Charge Anode Details Bare + commercial AEM Bare + commercial AEM Cathode Details 300 um, 6 wt% PVA, 20 wt% SSA coating 300 um, 6wt % PVA, 10 wt% SSA coting

12 S12 Table S4. Analysis of performance degradation during operation through comparison of performance parameters for early operation cycles (cycles 6 th through 10 th ) compared with later cycles (cycles 36 th through 40 th ). Each cycle is approximately 30 minutes. Electrode PVA - CDI PVDF - CDI PVA - PC - MCDI PVA - MCDI PVDF - MCDI Cycles Salt Absorptio n Capacity (mg/g) Avg. Salt Absorption Rate (mg/g/hr) Salt Removal (%) Charge (%) Coulombic (%) The Coulombic efficiency or round-trip charge efficiency is the ratio of moles of current discharged during desorption to that supplied during adsorption. Table S5. Performance degradation during operation through analysis of early operation cycles (cycles 6 th through 10 th ) compared with later cycles (cycles 36 th through 40 th ). The data show the percentage change in each metric from early to late operation cycles. Sample Configuration Salt Absorption Capacity Avg Salt Absorption Rate Salt Removal Charge Coulombic PVA - CDI % % % % 0.7 % PVDF - CDI % % % % 0.4 % PVA - PC - MCDI % % % % 0.5 % PVA - MCDI % % % % 0.9 % PVDF - MCDI % % % % 0.6 %