Article pubs.acs.org/IECR
Electroosmotic Flow in Cell Built with Electrodes Having Two Redox Couples Rudra Kumar, Kousar Jahan, Rajaram K. Nagarale,*,† and Ashutosh Sharma* Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208016, U.P., India S Supporting Information *
ABSTRACT: In an electroosmotic flow cell with two electrooxidizable and electroreducible reactants in its electrodes, the net cell reaction underlying the flow-driving proton flux from the anode to the cathode has three possible scenarios: (a) thermodynamically downhill, i.e., assisting the flow; (b) zero flow, which neither assists nor retards the flow; and (c) thermodynamically uphill, which retards the flow. A nongassing test cell was built with a ceramic membrane sandwiched between two identical electrodes comprising CeO2−x nanoparticle-decorated, nitrogen-containing graphene oxide sheets. We demonstrated the switching between the three possible flow and current regimes as reactants were exhausted in the redox active CeO2−x and the nitrogen-containing graphene electrodes.
■
INTRODUCTION Nongassing low DC voltage electroosmotic flow cells providing fluxes of 30−40 μL min−1 cm−2 V−1 have been built using consumable flow-through Ag/Ag2O1 electrodes, O2 plasmatreated carbon-paper electrodes,2 and redox-polymer electrodes like poly(hydroquinone/benzoquinone)3 and polyaniline electrodes.4 Having a single dominant proton-generating anode reaction and a single dominant proton-consuming cathode reaction balancing the anode reaction such that the net cell reaction is nil, their small (∼0.3 V) flow threshold was defined by the pH difference between the anode and cathode compartments, and their flow was constant for a particular applied voltage or current. Here, we consider an electroosmotic flow cell having a pair of similar electrodes, each capable of undergoing two different redox reactions: AH ↔A+ + H+ + e− and BH ↔ B+ + H+ + e−. Flow-driving protons are released in the forward reactions (AH→ A+ + H+ + e− and BH→ A+ + H+ + e−) of the cell’s anode and are consumed in the reverse reactions (A+ + H+ + e → AH and B+ + H+ + e → BH) of the cell’s cathode. The net cell reaction is nil, and an infinitesimally slow flow can start just above an applied voltage of 0 V when there is no net chemical change, i.e., when the anode reaction is AH → A+ + H+ + e− and the cathode reaction is A+ + H+ + e → AH or when the anode reaction is BH → B+ + H+ + e− and the cathode reaction is B+ + H+ + e → BH (i.e., when the electrode reactions are symmetrical opposites). When the cathode reaction is not the symmetrical opposite of the cathode reaction, i.e., when there is a net chemical change, the reaction can be a Gibbs free energy releasing reaction (i.e., spontaneous), or it can be a thermodynamically uphill reaction (i.e., Gibbs free energy consuming). The net cell reaction is not nil. When the anode reaction is AH → A+ + H+ + e− and the cathode reaction is B+ + H+ + e → BH, the net cell reaction is AH + B+ → BH + A+ ; when the anode reaction is BH → B+ + H+ + e− and the cathode reaction is A+ + H+ + e → AH, the net cell reaction is BH + A+ → AH + B+. It is necessarily true that if the reaction AH + B+ → BH + A+ is thermodynamically downhill (i.e., © XXXX American Chemical Society
spontaneous) and the cell voltage is positive (assisting the flow), then the reaction of the cell where the reverse reaction BH + A+ → AH + B occurs will be thermodynamically uphill, with a negative cell voltage retarding the flow. For this reason, depending on the time-dependent exhaustible electrooxidizable reactant amount in the anode and the time-dependent exhaustible electroreducible reactant amount in the cathode, an electroosmotic flow cell with two redox couples incorporated into each of its electrodes can be in one of three states: the net chemical reaction can assist the flow; the net chemical reaction can be nil, neither assisting nor retarding the flow; and the net chemical reaction can retard the flow. We found this to be true. The two-redox-couple electrodes of the electroosmotic flow cell that we studied had graphene oxide-cerium oxide (GOCeO2−x) electrodes. The aqueous solution-exposed surfaces of the CeO2−x particles comprised the hydrated but lattice-bound Ce3+/4+ redox couple.5 The redox potential of 10−20 nm CeO2−x nanoparticles is ∼0.21 V versus standard hydrogen electrode (SHE), which is nearly identical to the redox potential of the Ag/AgCl electrode.6 The nitrogen-containing graphene oxide comprises oxidizable and reducible nitrogen functions. The proton-generating anodic electrooxidation reactions are as follows: Ce3 + + H 2O → Ce 4 +OH− + H+ + e−
and =NH 2+ → =NH + H+ + e−
and the proton consuming cathodic electroreductions are as follows: Special Issue: Doraiswami Ramkrishna Festschrift Received: April 27, 2015 Revised: May 25, 2015 Accepted: May 28, 2015
A
DOI: 10.1021/acs.iecr.5b01568 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 1. Scheme of the synthesis of GO-CeO2−x.
Ce 4 +OH− + H+ + e− → Ce3 + + H 2O
dispersion in deionized water was prepared by ultrasonication. A 1 mM (434 mg) sample of cerium nitrate hexahydrate was added. After complete mixing, 1 mL of 25 wt % ammonia was added. The resulting mixture was transferred into a 40 mL Teflon-lined hydrothermal reactor containing a magnetic stirrer bar. The reactor was kept in an oil bath at 180 °C for 30 min at constant stirring. After the completion of the reaction, the autoclave was cooled to room temperature and the product was collected by simple filtration, washed thoroughly with distilled water several times, and vacuum-dried overnight. Preparation of Silica Membrane, Electrode, and Electroosmotic Pump. The silica membrane was prepared by pelletizing the monodisperse silica particles at 300 PSI as reported earlier.7 The flow-through electrodes were prepared by dip coating nickel foam with CeO2−x−G paste. The paste was prepared by homogenizing 200 mg of CeO2−x−G composite material in 20 mL of isopropanol and 1 mL of Nafion solution (5 wt % in water:isopropanol). Before coating, the nickel foam was treated with 1 M HCl to clean and remove the hydroxide of nickel. The washed foam was used for dip coating. The uniformly coated electrodes were dried in an oven at 100 °C for 1 h and used to make the pump after punching 8 mm diameter circular pieces as reported previously. For comparison, a paste of GO and RGO was prepared and coated on nickel foam. Characterization. The crystalline nature of CeO2−x−G was analyzed by X-ray diffraction (XRD) (PAN Analytic Germany) using Cu Kα radiation (λ = 1.5406 Å) from 5° to 80° at a 2° min−1 scan rate. X-ray photoelectron spectroscopy (XPS) measurements were carried out with Omicron ESCA Probe spectrometer with unmonochromatized Mg Kα X-rays (hν = 1253.6 eV). The spectra were deconvoluted to their component peaks using the software Casa XPS. For the determination of composition and oxidation states from the binding energy of the elements, full range XPS was carried out, i.e., 0−1000 eV. Morphological characterization was performed by field emission scanning electron microscopy (FESEM, ZEISS Supra 40VP, Germany). Elemental mapping was carried out with an energy dispersive X-ray spectroscopy (EDX) instrument from Oxford elemental system combined with FESEM. A transmission electron microscopy (TEM) instrument (TECNAI-G2) operated at 200 kV was used to visualize CeO2−x nanoparticles embedded on the graphene sheet and to record their selected area electron diffraction pattern (SAEDP). Highresolution transmission electron microscopy (HRTEM, FEI, TITAN) with elemental mapping was carried out at 300 kV. The surface functional group present in the composite was
and =NH + H+ + e− → =NH 2+
The redox potential of 10−20 nm CeO2−x nanoparticles is ∼0.21 V versus SHE, which is nearly identical to the redox potential of the Ag/AgCl electrode, suggesting their use as reference electrodes in subcutaneously implantable glucose sensors.6
■
EXPERIMENTAL SECTION Materials. Natural graphite flakes (200 mesh size) was purchased from Alfa Aser. Sulfuric acid, hydrochloric acid, potassium permanganate, sodium nitrate, hydrogen peroxide(30 wt % V/V), liquor ammonia (25 w/v%), and isopropanol were purchased from Fisher Scientific. Nafion solution (5 wt % in isopropanol) was purchased from Sigma-Aldrich. Cerium nitrate hexahydrate was supplied from Loba Chemicals. Nickel foam was purchased from MTI Corporation. All the chemicals were used as received. Synthesis of GO. Graphite oxide was synthesized by modified Hummer’s method.4 Briefly, 1 g of preoxidized graphite flake (∼45 μm) was mixed with 1 g of sodium nitrate and 46 mL of concentrated H2SO4 at 0 °C for 10 min in an ice bath. Next, 6 g of KMnO4 was added slowly while maintaining 20 °C temperature of the reaction mixture. The uniformly mixed solution was held at 35 ± 5 °C in water bath under constant stirring for about 2 h, resulting in a thick paste. Then, 80 mL of DI water was added into the paste and the mixture was stirred for 30 min while the temperature was raised to 95 °C. An additional 200 mL of DI water was added, followed by slow addition of 6 mL of 30% H2O2. After the complete addition of H2O2, the color of the solution was turned to yellow from initial dark brown. The thus obtained warm solution was filtered and washed with 30% concentrated HCl solution to remove residual sulfate ions. The filtered cake obtained was redispersed in 200 mL of DI water by mechanical stirring. Centrifugation was carried at low rpm (1000 rpm) for 2 min to remove the unexfoliated graphite. It was repeated for 2−3 times to remove the entire visible particle. The obtained supernatant was centrifuged at 8000 rpm for 15 min to collect GO flakes. The obtained precipitate was collected and vacuum-dried overnight at 60 °C in a vacuum oven. Synthesis of CeO2−x−G Composite. A simple one-step hydrothermal reaction was used to synthesize CeO2−x−G composite. In brief, 30 mL of 5 mg/mL graphene oxide B
DOI: 10.1021/acs.iecr.5b01568 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 2. (A) FTIR spectra of GO, RGO, and GO-CeO2−x. (B) Raman spectra of GO, RGO, and GO-CeO2−x. (C) TGA (N2 atmosphere) at 10 °C min−1 heating rate. (D) XRD of GO, RGO, and GO-CeO2−x recorded at 2° /min scan rate; Cu Kα radiation (λ = 1.5406 Å).
The GO-CeO2−x formation was monitored using FTIR (Figure 2A). The GO absorptions at 1740 and 1048 cm−1 showed the CO and C−OH vibrations of the COOH functions, respectively. In addition, the epoxide functions showed an absorption at 1235 cm−1, and the absorptions at 3420 and 1390 cm−1 represented the OH functions.8 The water on the GO showed an absorption at 1625 cm−1, whereas the reduced GO, i.e., the graphene sheet without oxygen (G), showed absorptions at 1632, 1627, 1564, and 1540 cm−1;9 and cerium oxide (i.e., Ce−O) showed an absorption at 552 cm−1.10 Figure 2B shows the Raman spectra of GO, RGO, and GOCeO2−x. The peaks at 1352 and 1590 cm−1 are the D and G bands of GO, with the D band being that of disordered graphitic and k-point phonons of the A1g symmetry11 associated with the −CO, −OH, and −COOH functions, and the G band is that of the in-plane stretching of sp2 hybridized carbons, i.e., E2g phonons.12 The ∼463 cm−1 peak is attributed to Ce− O.13 Figure 2C shows the results of thermogravimetric analyses of GO and GO-CeO2−x under nitrogen. GO retains ∼32% of its initial weight, while the GO-CeO2−x retains ∼74% of its weight when heated to 800 °C.14 The weight losses for the GO and GO-CeO2−x are attributed to drying and the loss of oxygencontaining functional groups.15 The presence of CeO2−x on the GO was confirmed by its Xray diffraction pattern (Figure 2D). The 11.20° peak of GO is assigned to its (001) plane, with a spacing of 0.83 nm, which is consistent with oxygen-containing functions on the graphene sheets.10 The expansion of the d spacing from 0.34 nm for graphite16 to 0.83 nm for GO confirms the complete exfoliation. The 25.6° peak of the hydrothermally treated RGO is assigned to the (002) plane, with an interplanar distance of 0.37 nm. The 2θ peaks of 28.7°, 33.2°, 47.7°, 56.6°, 59.3°, 69.7°, and 77° are assigned to the (111), (200), (220),
determined by Fourier transfrom infrared spectroscopy (FTIR; Tensor 27, Bruker, Germany) over the wavenumber range of 400−4000 cm−1. UV−visible spectra were recorded with a Varian Cary 50 Bio spectrophotometer (United States). Raman spectroscopy (model, Alpha; make, Witec, Germany) was performed in the frequency range of 400−3000 cm−1 with 514 nm laser source to determine the stretching of ceria and GO. Thermogravimetric analysis (TGA) was carried out on a TA Instruments 2960 instrument at a heating rate of 10 °C/min under nitrogen flow. Atomic force microscopy (Agilent Pico View 1.14.2, United States) measurements of GO and CeO2−x−G composites were analyzed in noncontact mode. Before analysis, all the samples were coated on the surface of a freshly cleaved mica sheet. The flow of prepared EOP was measured using custom-built equipment as reported.7 CHI 760E electrochemical analyzer (CH Instruments, USA) was used for the supply of constant potential. Cyclic voltammetry was performed in PBS buffer at pH 7 with the potential range from −0.2 to 0.8 V. The CeO2−x−G composite was coated on the nickel foam and acted as working electrode, while Ag/AgCl (3 M KCl) and platinum wire were used as reference and counter electrodes, respectively.
■
RESULTS AND DISCUSSION Synthesis and Characterization of Electrode Materials. Graphene oxide CeO2−x (GO-CeO2−x) was synthesized in a one-step hydrothermal reaction of a mixture of GO dispersed in DI water to which Ce(NO3)3 and then NH4OH was added. The reaction (Figure 1) was carried out in a Teflon-lined hydrothermal reactor at 180 °C for 30 min. After cooling to ambient temperature, the solid GO-CeO2−x was collected and washed with DI water, and then with isopropanol and dried. The produced graphene oxide sheets had uniformly distributed 5−7 nm CeO2−x nanoparticles. C
DOI: 10.1021/acs.iecr.5b01568 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Flux and Stall Pressure. Electroosmotic flow cells were fabricated by sandwiching a silica frit between nickel-foam flowthrough electrodes coated with GO, RGO, or GO-CeO2−x. Figure 5a shows the initial linearity of the applied voltage dependence of the flow rate. The initial threshold potential for the flow was 0.5 V, observed in flow cells made with GOCeO2−x and RGO electrodes. In contrast, with the GO, flow was observed only above 2 V. In flow cells built with GOCeO2−x electrodes, no gassing was seen even at 5 V, where electrolysis was thermodynamically allowed. The flux in the flow cells built with the GO-CeO2−x electrodes was 34 μL min −1 cm −2 V −1 , which exceeded the 8.8 and 17.8 μL min−1 cm−2 V−1 fluxes of the flow cells built with the GO and RGO electrodes, respectively. The higher flux in the flow cells built with RGO compared to those with GO was attributed to the better conductivity of RGO and to the presence of redox functions, which were introduced in the hydrothermal reaction with ammonia, exemplified by aromatic amines reversibly oxidized to imines, as seen by XPS (Figure S4 in the Supporting Information). The observed binding energies of 398.5, 399.5, 401.5, and 402.5 eV were consistent with the presence of −NC−, −NH−C−, −pyridine nitrogen, and N+H− functions,19 respectively. The flux of 34 μL min−1 cm−2 V−1 in the flow cells built with the GO-CeO2−x electrodes approached the 40 μL min−1 cm−2 V−1 flux of flow cells built with NH2-G/PANI electrodes4 and exceeded the 33 mL min−1 flux at 100 V of flow cells built with PEDOT-blended PSS electrodes.20 This flux was lower than the 93 ± 3 μL min−1 cm−2 flux at 1 V for Ag/silica frit/Ag2O7 electrodes and 2 orders of magnitude lower than the 2600 μL min−1 cm−2 V−1 flux for an EOP built with a 15 nm thick porous silica membrane and Pt electrodes.21 In an EOP built with Pt electrodes and an ion exchange membrane,22 the flux is ≫6 μL min−1 mA−1 cm−2 at 30 V. Figure 5b shows the flow-opposing pressure dependence of the flux of flow cells built with GO-CeO2−x electrodes. As in other EOPs, the stall pressure increases with the applied voltage. The stall pressures are 1.3, 2.1, and 3 kPa at 1, 2, and 3 V, respectively. In comparison, a pump built with Ag/Ag2O electrodes had a stall pressure of about 1 kPa near 0.25 V.7 However, the flux of these flow cells was degraded by silver contamination of their membranes.7 Coulombic Capacities of the Components. The GOCeO2−x composite electrodes comprised two consumable components, each with a different anodic and cathodic columbic capacity. The upper limit of the Coulombic capacities of the loaded CeO2−x on the 0.28 cm2 geometrical area electrodes was estimated as follows. Of the ∼12 mg of GOCeO2−x loaded on each electrode, 42% or 5.0 mg of CeO2−x was left after combustion in the thermogravimetric analyzer (TGA) (Figure 2C). If half the CeO2−x was electrooxidizable and half was electroreducible, the associated Coulombic capacities would be 1.4 C. On the basis of the XPS data (Figure 8A), only 26% was the electrooxidizable Ce(III), i.e., the Coulombic capacity of the anode was 0.7 C. The cell was operated for 16 h (Figure 6), during which a charge of 1.1 C passed, i.e., 0.4 C originated in the electrooxidizable RGO, weighing 7 mg (Figure S4 in the Supporting Information). Flow Domains. As discussed in the Introduction, three flow domains are expected when a cell operates at a constant applied voltage: a domain where the flow is assisted by the net cell reaction, a domain where the flow is neither assisted nor retarded because the net cell reaction is nil, and a domain
(311), (222), (400), and (331) planes, respectively, confirming the presence of face-centered cubic fluorite, space group Fm3̅m, CeO2−x (JCPDS 34-0394).13,17 The UV−vis spectra of GO, RGO, and GO-CeO2−x are provided in Figure S1 in the Supporting Information. The 232 nm peak of GO is a CC π−π*, and the 300 nm peak is a C O n-π* transition.18 In RGO, the 232 nm peak of GO is redshifted to 270 nm because the removal of the conjugationinterrupting oxygen restores the well-conjugated graphene. CeO2−x nanoparticles absorb at 320 nm.10 Figure 3 shows SEM images of the GO and GO-CeO2−x. The surface of GO is smooth, and its sheets are crumpled (Figure
Figure 3. SEM images of (a) GO and (b) GO-CeO2−x and (c, d) magnified views of GO-CeO2−x.
3a). The GO-CeO2−x sheets carry uniformly distributed 5−7 nm CeO2−x nanoparticles. These are seen in the magnified images (Figure 3c,d). The elemental EDX mapping (Figure S2 in the Supporting Information) confirms that the nanoparticles consist of CeO2−x. Figure 4 shows TEM images of the GO and GO-CeO2−x. The wrinkling of the GO sheet is seen in Figure 4a, and the
Figure 4. TEM image of GO (a) and the GO-CeO2−x (b, c). The inset in panel b shows the SAED pattern of the GO-CeO2−x.
uniformly distributed CeO2−x nanoparticles of GO-CeO2−x are seen in Figure 4b. The inset of Figure 4b, showing the selected area electron diffraction pattern of the GO-CeO2−x, confirms the cubic structure of the CeO2−x nanoparticles.10 The HRTEM image of Figure 4c shows (111) planes and CeO2−x particle diameters of 5−7 nm. The CeO2−x nanoparticles act as spacers, preventing the stacking of GO sheets. The presence of the CeO2−x nanoparticles was further supported by atomic force microscopy (AFM) in the noncontact mode (Figure S3 in the Supporting Information). The height profiles for the GO and GO-CeO2−x are ∼1 nm and ∼10 nm, respectively, which are consistent with the protrusion of 5−7 nm CeO2−x nanoparticles from a smooth surface. D
DOI: 10.1021/acs.iecr.5b01568 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 5. (a) Dependence of the flow rate on the applied voltage. The slopes are GO, 2.45; RGO, 5.00; and GO-CeO2−x, 9.55 μL min−1 V −1. (b) Dependence of the flow rate on the opposing pressure.
Anodic and Cathodic CeO2−x Reactions. The expected consumptions of the Ce3+ of the anode and the Ce4+ of the cathode are seen in the XPS spectra after its exhaustion. Figure 8a shows the deconvoluted XPS spectra for the as-synthesized GO-CeO2−x composite. The peaks at 880−901 and 907−917 eV are for the Ce 3d5/2 and Ce 3d3/2, respectively, with the peaks at 885.1 and 900.5 eV being those for Ce3+.23 The peaks at 882.7, 898.8, and 901.3 eV are for the Ce 3d5/2 of Ce4+.24 The fraction of Ce3+ was calculated from the ratio of the Ce3+ peak heights to all the peak heights.23 Prior to starting the flow, the percentage of Ce3+ was 26%. After exhaustion, the percentage of Ce3+ dropped to 11% in the anode and increased to 36% in the cathode (Figure 8b,c), as expected for the reactions
Figure 6. Time dependence of the flow rate at constant 2 V applied voltage. The average current and flow rate were measured hourly.
Ces 3 + + H 2O → Ces 4 +OHs− + H+ + e− (anode)
and
where the flow is retarded by the net cell reaction. Figure 6 shows a high-flow-rate domain in the initial 240 min period, a smaller flow rate in the 240−780 min period, and an even smaller flow rate in the 780−960 min period, which could be attributed to the expected operating domains. Another factor that dominates the decrease in flow over time accompanied by an increased current is the electrooxidation of imine to ammonia. The effect on the flow solution of adding ammonia is shown in Figure 7. As clearly seen, a small amount of electrogenerated ammonia has a great effect on the flow rate.
Ces 4 +OHs− + H+ + e− → Ces 3 + + H 2O (cathode)
A schematic of the process is shown in Figure 8d. Changes in the Graphene of the Anode and the Cathode. The changes in the surface morphologies, crystal structures, and chemical compositions of the anode and cathode were found using FESEM and XRD. Panels a and b of Figure 9 show SEM images of the exhausted anode and cathode, respectively. The electrooxidized anodic graphene sheet was wrinkled, whereas the electroreduced cathodic sheet was not.
■
CONCLUSION We successfully demonstrated a nongassing test cell built with a ceramic membrane sandwiched between two identical electrodes comprising CeO2−x nanoparticle-decorated, nitrogencontaining graphene oxide sheets and having two redox centers. The primary electroosmotic flow, i.e., flow-driving proton flux, was obtained by thermodynamically favorable anode and cathode reactions, i.e., uphill reaction. Over time, the flow was decreased with thermodynamically less favorable electrode reactions and/or the electrogeneration of ammonia by the electrooxidation of graphitic imine moieties (a thermodynamically uphill reaction), which retarded the flow. Because both the CeO2−x and nitrogen-containing graphene were redox active, as the reactants were exhausted, the flow and current switched between the three possible states: thermodynamically favorable, retarding, and neither favorable nor retarding.
Figure 7. Effect of added ammonia in flowing solution. The flow cell was operated for 5 min at constant potential of 2 V. In the graph, the ammonia concentration is written above the trace and the corresponding flow rate below the trace. E
DOI: 10.1021/acs.iecr.5b01568 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 8. (a) XPS spectrum of unused GO-CeO2−x electrodes. (b) Deconvoluted XPS spectrum of the exhausted GO-CeO2−x anode. (c) Deconvoluted XPS spectrum of the exhausted GO-CeO2−x cathode. (d) Scheme of the CeO2−x reactions.
■
ACKNOWLEDGMENTS R.K.N. thanks the Department of Science & Technology (DST), Government of India, for Ramanujan Fellowship (SR/ S2/RJN-18/2011) award and financial support (Grant SR/S3/ CE/034/2013). This work was supported by the Department of Science & Technology, India.
■
Figure 9. Surface morphology of the exhausted GO-CeO2−x (a) anode and (b) cathode.
■
(1) Shin, W.; Lee, J. M.; Nagarale, R. K.; Shin, S. J.; Heller, A. A Miniature, Nongassing Electroosmotic Pump Operating at 0.5 V. J. Am. Chem. Soc. 2011, 133, 2374−2377. (2) Lakhotiya, H.; Mondal, K.; Nagarale, R. K.; Sharma, A. Low Voltage Non-Gassing Electro-Osmotic Pump with Zeta Potential Tuned Aluminosilicate Frits and Organic Dye Electrodes. RSC Adv. 2014, 4, 28814−28821. (3) Sachan, V. K.; Singh, A. K.; Jahan, K.; Kumbar, S. G.; Nagarale, R. K.; Bhattacharya, P. K. Development of Redox-Conducting Polymer Electrodes for Non-Gassing Electro-Osmotic Pumps: A Novel Approach. J. Electrochem. Soc. 2014, 161, H3029−H3034. (4) Kumar, R.; Kousar, J.; Nagarale, R. K.; Sharma, A. Non-Gassing Long Lasting Electroosmotic Pump with Polyaniline-Wrapped Aminated Graphene Electrodes. ACS Appl. Mater. Interfaces 2015, 7, 593−601. (5) Henderson, M. A.; Perkins, C. L.; Engelhard, M. H.; Thevuthasan, S.; Peden, C. H. F. Redox Properties of Water on the Oxidized and Reduced Surfaces of CeO2(111). Surf. Sci. 2003, 526, 1− 18. (6) Nagarale, R. K.; Hoss, U.; Heller, A. Mixed-Valence Metal Oxide Nanoparticles as Electrochemical Half-Cells: Substituting the Ag/AgCl of Reference Electrodes by CeO2−x Nanoparticles. J. Am. Chem. Soc. 2012, 134, 20783−20787. (7) Nagarale, R. K.; Heller, A.; Shin, W. A Stable Ag/CeramicMembrane/Ag2O Electroosmotic Pump Built with a Mesoporous Phosphosilicate-on-Silica Frit Membrane. J. Electrochem. Soc. 2011, 159, 14−17.
ASSOCIATED CONTENT
S Supporting Information *
UV−vis spectra, EDX with elemental mapping, AFM of GO and GO-CeO2−x, XRD of the anode and the cathode after 16 h of flow, XPS of RGO, deconvoluted XPS spectra of C and O for anode and cathode (Figures S1−S8). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b01568.
■
REFERENCES
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. Present Address †
R.K.N.: Central Salt and Marine Chemicals Research Institute, Gijubhai Badheka Marg, Bhavnagar-364002, Gujarat, India. Notes
The authors declare no competing financial interest. F
DOI: 10.1021/acs.iecr.5b01568 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research (8) Wu, N.; She, X.; Yang, D.; Wu, X.; Su, F.; Chen, Y. Synthesis of Network Reduced Graphene Oxide in Polystyrene Matrix by a TwoStep Reduction Method for Superior Conductivity of the Composite. J. Mater. Chem. 2012, 22, 17254−17261. (9) Liu, C.; Hao, F.; Zhao, X.; Zhao, Q.; Luo, S.; Lin, H. Low Temperature Reduction of Free-Standing Graphene Oxide Papers with Metal Iodides for Ultrahigh Bulk Conductivity. Sci. Rep. 2013, 4. (10) Srivastava, M.; Das, A. K.; Khanra, P.; Uddin, M. E.; Kim, N. H.; Lee, J. H. Characterizations of in Situ Grown Ceria Nanoparticles on Reduced Graphene Oxide as a Catalyst for the Electrooxidation of Hydrazine. J. Mater. Chem. A 2013, 1, 9792−9801. (11) Ferrari, A. C.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 61, 14095−14107. (12) Cancado, L. G.; Pimenta, M. A.; Neves, B. R. A.; Dantas, M. S. S.; Jorio, A. Influence of the Atomic Structure on the Raman Spectra of Graphite Edges. Phys. Rev. Lett. 2004, 93, 247401. (13) Jiang, L.; Yao, M.; Liu, B.; Li, Q.; Liu, R.; Lv, H.; Lu, S.; Gong, C.; Zou, B.; Cui, T.; Liu, B.; Hu, G.; Wagberg, T. Controlled Synthesis of CeO2/Graphene Nanocomposites with Highly Enhanced Optical and Catalytic Properties. J. Phys. Chem. C 2012, 116, 11741−11745. (14) Jha, S. K.; Kumar, C. N.; Raj, R. P.; Jha, N. S.; Mohan, S. Synthesis of 3d Porous CeO2/Reduced Graphene Oxide Xerogel Composite and Low Level Detection of H2O2. Electrochim. Acta 2014, 120, 308−313. (15) Zhang, Y.; Ma, H.-L.; Zhang, Q.; Peng, J.; Li, J.; Zhai, M.; Yu, Z.Z. Facile Synthesis of Well-Dispersed Graphene by Gamma-Ray Induced Reduction of Graphene Oxide. J. Mater. Chem. 2012, 22, 13064−13069. (16) Amarnath, C. A.; Hong, C. E.; Kim, N. H.; Ku, B.-C.; Kuila, T.; Lee, J. H. Efficient Synthesis of Graphene Sheets Using Pyrrole as a Reducing Agent. Carbon 2011, 49, 3497−3502. (17) Huang, K.; Li, Y. H.; Lin, S.; Liang, C.; Xu, X.; Zhou, Y. F.; Fan, D. Y.; Yang, H. J.; Lang, P. L.; Zhang, R.; Wang, Y. G.; Lei, M. OneStep Synthesis of Reduced Graphene Oxide-CeO2 Nanocubes Composites with Enhanced Photocatalytic Activity. Mater. Lett. 2014, 124, 223−226. (18) Kuila, T.; Mishra, A. K.; Khanra, P.; Kim, N. H.; Uddin, M. E.; Lee, J. H. Facile Method for the Preparation of Water Dispersible Graphene Using Sulfonated Poly(Ether-Ether-Ketone) and Its Application as Energy Storage Materials. Langmuir 2012, 28, 9825− 9833. (19) Hu, T.; Sun, X.; Sun, H. T.; Xin, G. Q.; Shao, D. L.; Liu, C. S.; Lian, J. Rapid Synthesis of Nitrogen-Doped Graphene for a Lithium Ion Battery Anode with Excellent Rate Performance and Super-Long Cyclic Stability. Phys. Chem. Chem. Phys. 2014, 16, 1060−1066. (20) Erlandsson, P. G.; Robinson, N. D. Electrolysis-Reducing Electrodes for Electrokinetic Devices. Electrophoresis 2011, 32, 784− 790. (21) Snyder, J. L.; Getpreecharsawas, J.; Fang, D. Z.; Gaborski, T. R.; Striemer, C. C.; Fauchet, P. M.; Borkholder, D. A.; McGrath, J. L. High-Performance, Low-Voltage Electroosmotic Pumps with Molecularly Thin Silicon Nanomembranes. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 18425−18430. (22) Brask, A.; Kutter, J. P.; Bruus, H. Long-Term Stable Electroosmotic Pump with Ion Exchange Membranes. Lab Chip 2005, 5, 730−738. (23) Joung, D.; Singh, V.; Park, S.; Schulte, A.; Seal, S.; Khondaker, S. I. Anchoring Ceria Nanoparticles on Reduced Graphene Oxide and Their Electronic Transport Properties. J. Phys. Chem. C 2011, 115, 24494−24500. (24) Deshpande, S.; Patil, S.; Kuchibhatla, S. V. N. T.; Seal, S. Size Dependency Variation in Lattice Parameter and Valency States in Nanocrystalline Cerium Oxide. Appl. Phys. Lett. 2005, 87, 3113.
G
DOI: 10.1021/acs.iecr.5b01568 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
