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Effects of Graphene Oxide on Proton Exchange Membrane Fuel Cells Henry Ho, Jesse Matsuda, Mailun Yang, Likun Wang, Miriam Rafailovich Materials Science and Chemical Engineering Department, Stony

1 Effects of Graphene Oxide on Proton Exchange Membrane Fuel Cells Henry Ho, Jesse Matsuda, Mailun Yang, Likun Wang, Miriam Rafailovich Materials Science and Chemical Engineering Department, Stony Brook, NY, 11794, USA Abstract Proton exchange membrane fuel cells (PEMFCs) have a high power density that is capable of producing clean and reliable energy. In order to commercialize PEMFCs, power output must be improved while reducing costs therefore we focus on the use and viability of graphene oxide on Nafion membranes and electrodes for use in PEMFCs. A GO solution is prepared by measuring out methanol, water, and GO powder and sonicating the solution. After sonication, the solution is applied as a monolayer onto Nafion using a Langmuir- Blodgett Trough (LB-Trough) which produces our experimental proton exchange membrane (PEM). This is conducted with the goal of increasing the efficiency of the fuel cell. The fuel cell was initially tested on a small single cell test station. Afterwards the fuel cell was tested using our large cell test station. Using the same technique to produce the GO PEM, a membrane electrode assembly (MEA) was produced consisting of the PEM sandwiched between two platinum (Pt) electrodes and subsequently hot pressed. Variables such as relative humidity, temperature and gas flow is controlled. With the GO applied, the fuel cell is able to yield a higher power output compared to the control, which is the standard PEMFC without GO modifications. The polarization curve that was generated using current density and power density showed that the fuel cell with GO was able to output more power per square centimeter at W/cm 2, an increase of 22.1%, compared to the power per square centimeter at W/cm 2 of the control fuel cell. 1. Introduction With the world s increasing energy demand, PEMFCs have the potential to become a prominent source of renewable energy production. An attractive aspect of PEMFCs is the lack of toxic emissions from the production of energy as the only products are water and energy. Figure 1 shows the basic diagram of a fuel cell. The left side is the anode in which the H2 gas enters. The cathode is the right side in which it is either connected to O2 or to atmosphere. The center consists of the proton exchange membrane or a specific electrolyte. Here a proton is stripped of its electrons. The electrons are then used to create power by forcing them through a circuit as they are unable to pass through the electrolyte due to the membrane. At the cathode, the protons react with oxygen to produce water. Figure 1. Basic Diagram of a PEMFC. [1] 85

2 At the current state of research, energy produced from PEMFCs is limited by the financial costs associated with the miniscule amount of energy produced in relation to the initial cost. The major barriers that hinder commercialization of PEMFCs are associated with cost, performance, and durability. The cost is due to the use of expensive platinum catalyst to promote the reaction; therefore, alternative catalyst components are being investigated for lower cost while maintaining performance. Performance and durability of the PEMFC can be improved by improving the MEA through mitigating degradation. The Department of Energy has imposed a standard for commercial fuel cells to operate for 40,000 hours when stationary and 5,000 hours when in transit [1]. Since 2006, the cost of automotive fuel cells has decreased by more than 50% while durability has doubled [2]. The cause of such is done by utilizing a platinum alloy to reduce the amount of platinum and by improving the MEA. Yet it is still possible to further improve on this technology. Our goal is to enhance the power output of PEMFCs. This can be done by enhancing the power output by using inexpensive material. The PEMFC output can be increased by improving the membrane or the electrode. The membrane of PEMFCs is one of the core components that has drawn considerable attention to it in regards to what material should be used. Currently, Nafion membranes produced by Dupont represent most PEMFCs. The unique structure of the Nafion membranes provide chemical stability as well as desirable proton conductivity under 100% relative humidity [3]. However, the proton conductivity of Nafion membranes is extremely dependent on the presence of water. At elevated temperatures or low relative humidity, a sharp decline in proton conductivity is noticed for the Nafion membrane due to dehydration [4]. As such, one approach in aiding the membrane conductivity at low relative humidity and elevated temperatures is by incorporating hydrophilic inorganic additives into Nafion membranes to improve water retention capacity [5]. Graphene oxide (GO) is considered as an amphiphilic material with hydrophilic regions containing oxygenic groups and may be utilized as an inorganic additive in conjunction with Nafion membranes for its unique twodimensional structure and high surface area [6,7]. GO is a promising material for PEMFCs due to its excellent mechanical and chemical properties. The functional groups of GO allow it to have exceptional properties in reduction oxygen reactions as well as making it a better support than traditional platinum on carbon electrodes for the catalysts involved in PEMFCs [8]. The main functional group in GO is epoxide that acts potential once water molecules bind to the sites, this occurs even at low relative humidity and at room temperature [9]. Figure 2 illustrates the interaction between the epoxide group and water molecules as well as how predicted movement of proton transfer. Figure 2. Illustration of proton conduction on epoxide groups. [10] Studies have indicated GO can be implemented in MEAs to enhance the performance of PEMFCs. We conducted 86

3 experiments to analyze the effects on GO on Nafion membranes and determine if the product meets and exceeds expectations. Two methods of preparation are used; applying GO solution with a Langmuir- Blodgett Trough (LB-Trough) and by spray coating the Nafion. The resulting coated membranes were tested in fuel cell test stations to determine current and power densities. 2. Experimental Section 2.1 Experimental Methods Creating GO solution The Nano Graphene Oxide (NGO) Powder (purchased from Graphene Supermarket) is used to create a Graphene Oxide Solution. The solution consists of 5 ml methanol, 1 ml DI water, 6 mg graphene oxide. The solution is sonicated using Branson 3510 for 40 minutes before stored. This solution was homogenous Creating GO and Nafion Solution A solution consisting of 5 ml methanol, 1 ml DI water, 6 mg graphene oxide, and 18 ml liquid Nafion is mixed thoroughly using a sonication machine for 40 minutes. This solution was homogenous Coating Nafion 117 with GO solution The graphene oxide solution was applied to the Nafion 117 (Purchased from DuPont) membrane by utilizing the Langmuir-Blodgett Trough. One half ml (0.50) of the GO solution was added to each side of the trough. The barriers are set to close at a rate of 8 cm 2 /minute until it hit a target of 50 mn/m on the platinum sensor. While the barriers were closing, 0.25 ml of GO solution was added to each side every 100 cm 2. The Nafion 117 membrane is then lifted GO Nafion 117 on small test station The Nafion 117 is hydrated in DI water for 5 minutes. It is then placed in between two Commercial Platinum Carbon (0.1 mg/cm 2 ) Gas Diffusion Electrodes which were purchased from FuelCellsEtc.com and tested using the small test station. The cathode is open to atmosphere while the anode connects to H2. The H2 gas flow rate is set to 78 ccm Spraying Electrodes with GO solution A similar solution of GO is sprayed onto Nafion membrane using an air spray gun GO electrodes on small test station This MEA is tested under the same conditions as the coated experiment on the small test station. The test station is shown in figure Coating Nafion 212 with GO solution The same steps were conducted in regards to coating the Nafion 117 with the LB-trough. Once the coated membrane is obtained, it is placed in between two electrodes. This MEA is then hot pressed using Carver hydraulic unit model #3912 at 130 C for two minutes for the electrodes to adhere to the membrane GO Nafion 212 in large test station The MEA is placed into the large test station, (University Test Stations from FuelCellTechnologies.com) shown in figure 4. The large test station temperature is set to 60 C, no back pressure, and 100% relative humidity. Current density is increased stepwise from 0.0 A/cm 2 to 7.0 A/cm 2 at set intervals, minimum gas flow rate of 50 sccm for H2 and minimum gas flow rate of 100 sccm for O2. The gas flows were concertedly increased as the current increased. 87

2.2 Analytical Methods 2.2.1 Isothermal Curves Isothermal curves are obtained from the use of the LB-trough to analyze the pressure as a function of surface area.

Three assemblies are prepared: control, sprayed, and coated. The control refers to the MEA that has no GO applied. The sprayed assembly has the electrodes sprayed with GO solution.

4 2.2 Analytical Methods Isothermal Curves Isothermal curves are obtained from the use of the LB-trough to analyze the pressure as a function of surface area. This is to analyze the ability of the solutions to maintain a monolayer Polarization Curves The data collected by the fuel cell test stations allow us to create polarization curves. Three assemblies are prepared: control, sprayed, and coated. The control refers to the MEA that has no GO applied. The sprayed assembly has the electrodes sprayed with GO solution. Lastly, the coated membrane refers to the assembly with the Nafion membrane coated with GO using the LB-trough. The polarization curves allow us to visualize which fuel cell will yield the higher output. These polarization curves were obtained using the following test stations: Small Test Station and the Large Test Station. Figure 3. Small Test Station The small test station provides hydrogen to the fuel cell but is also open to air. The fuel cell would be influenced by ambient temperature and humidity. The large test station allows us to control these parameters. Figure 4. Large Test Station 3. Results and Discussion Figure 5 depicts voltage and power density vs current density for the control fuel cell, the GO coated fuel cell, and the GO sprayed fuel cell. The fuel cell that has the membrane coated with GO through the LB-trough yields the highest voltage to current density and power density. The next is the fuel cell that has its electrode sprayed with GO. Finally, the control has the lowest values of the three as shown in Figure 7. We determined that the use of GO spray is an inefficient means of applying GO as the particles tended to accumulate on the surface of the nozzle preventing GO from being applied as well as developing an uneven coating on the membrane. A suggested method in improving this process to make this a viable option is to use an air spray gun made of a material that GO does not adhere to. As it is determined that the GO coat is more beneficial, we moved onto testing the GO coat in the large test station. Figure 6 88

5 shows that the GO coat can output roughly 22.0% more than the control at the peak, 0.95 W/cm 2 vs 0.78 W/cm 2. Figure 6 shows that when operating at 0.6V the standard PEMFC can output W/cm 2 whereas the PEMFC with GO coating can output W/cm 2. Tateishi et al had results of their paper GO to reach power density output at approximately 0.93 mw/cm 2 at 0.6V, about one third of the output from the LB-trough coated membrane [9]. From the isothermal curve that is created during the application of GO via LB-trough, we theorized that the GO monolayer continuously deformed and folded over, creating a multilayer. The steady decrease shown in Figure 8. The increase is a result of adding GO solution as the surface area decreased every 100 cm 2. The monolayer formed from the GO solution constantly fell apart meaning that a stable monolayer is not present throughout the application. However, by introducing liquid Nafion into the GO solution, the isothermal curve procured from the LBtrough, Figure 9, shows that no collapse occurred. Figure 9 instead shows that the surface pressure increases showing that the layers were being pushed on top of the water rather than into the water. This means that the monolayer formed with the addition of liquid Nafion held up significantly better than the GO solution without liquid Nafion. The Nafion is able to support the formation of a layer because it contains both hydrophilic and hydrophobic areas. Liquid Nafion contains sulfonic acid functional groups that self-organize into arrays of hydrophilic water channels. Interspersed between the hydrophilic channels are hydrophobic polymer backbones which provide mechanical stability. Figure 5. A graph of the current densities and power densities of the control, GO coated, and GO sprayed obtained from the small test station. Figure 6. A graph of the current densities and power densities of the control and GO coated obtained from the large test station. Figure 7. Histogram depicting the power density at 0.6V. 89

6 Figure 8. Isothermal curve that is obtained from LB-trough for GO solution. 4. Conclusion The gathered data indicates that GO has a beneficial effect on the PEMFC. Coating the Nafion membrane has a larger effect on the PEMFC and efficiency than spraying the electrodes. A suggested method in improving the spraying process to make it a viable option is to use an air spray gun made of a material that GO does not adhere to. Figure 6 shows that the power density for the coated is 22.0% higher than the control at peak output. Based on the analysis, it is apparent that the most efficient method in enhancing the output of PEMFCs is the coating of the membrane with GO. The GO and nafion solution is also shown to be able to form layers whereas the GO solution has a preference to enter the water instead of creating a layer. Acknowledgements We gratefully acknowledge the educational support from the Department of Chemical and Molecular Engineering at Stony Brook University. The guidance from Miriam Rafailovich, Clement Marmorat, and Likun Wang has been invaluable. References [1] Department of Energy. Fuel Cells. Figure 9. Isothermal curve that is obtained from LB-trough for GO and Nafion Solution (accessed Dec 21, 2016). [2] Department of Energy. Fuel Cell Technologies Office: Accomplishments and Progress. hnologies-office-accomplishments-and-prog ress (acessed Dec 21, 2016). [3] Zhang, H.; Shen, P. Recent development of polymer electrolyte membranes for fuel cells. Chem. Rev. 2012, 112, [4] Hickner, M.A.; Ghassemi, H.; Kim, Y.S.; Einsla, B.R.; McGrath. J.E. Alternative polymer systems for proton exchange membranes (PEMs) Chem. Rev. 2004, 104, [5] Tripathi, B.P. ; Shahi, V.K. Organicinorganic nanocomposite polymer electrolyte membranes for fuel cell applications. Prog. Polym. Sci. 2011, 36, [6] Chen, D.; Feng, H.; Li, J. Graphene oxide: preparation, functionalization, and electrochemical applications. Chem. Rev. 2012, 112, [7] Chien, H.-C.; Tsai, L.-D.; Huang, C.-P.; Kang, C.-y.; Lin, J.-N.; Chang, F.-C. Sulfonated graphene oxide/nafion composite membranes for high-performance direct methanol fuel cells. Int. J. Hydrogen Energ. 2013, 38, [8] Devrim, Y.; Albostan, A. Graphene Supported Platinum Catalyst-Based Membrane Electrode Assembly for PEM Fuel Cell. J. Electron. Mater. 2016, 45.8, [9] 90

7 Tateishi, H.; Hatakeyama K.; Ogata, C.; et al. Graphene Oxide Fuel Cell. J. of the Electrochem. Soc. 2013, 106, F1175-F1178. [10] Koinuma, M.; Ogata, C.; Kamei, Y.; et al. Photochemical Engineering of Graphene Oxide Nanosheets. J. Phys. Chem. 2012, 116,

Atomic Layer Deposition of TiO 2 support on PEM to Increase Fuel Cell Electrode Durability by CO Oxidation Enhancement

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