Low Permeation Liner For Hydrogen Gas Storage Tanks

Hydrogen, Fuel Cells, and Infrastructure TechnologiesFY 2003 Progress ReportLow Permeation Liner for Hydrogen Gas Storage TanksPaul A. Lessing (Primary Contact)Idaho National Engineering & Environmental Laboratory (INEEL)P.O Box 1625Idaho Falls, ID, 83415-2218Phone: (208) 526-8776; Fax: (208) 526-0690; E-mail: pal2@inel.govDOE Technology Development Manager: Lucito CataquizPhone: (202) 586-0729; Fax: (202) 586-9811; E-mail: Lucito.Cataquiz@ee.doe.govINEEL Technical Advisor: Raymond P. AndersonPhone: (208) 526-1623; Fax: (208) 526-9822; E-mail: anderp@inel.govSubcontractor: University of California at Los Angeles (UCLA), Los Angeles, CAObjectives Develop a polymer liner that greatly limits hydrogen losses from commercial, light-weight, composite,high-pressure hydrogen tanksTechnical BarriersThis project addresses the following technical barriers from the Hydrogen Storage section of theHydrogen, Fuel Cells and Infrastructure Technologies Program Multi-Year R,D&D Plan: A.B.C.I.CostWeight and VolumeDurabilityMaterialsApproach Select and fabricate polymeric materials with the necessary electron and proton conducting propertiesto form an electrochemical tri-layer barrier to hydrogen permeation through polymer tank-linersFabricate “bench-top” models of the tri-layers on polymer substratesDemonstrate the successful functioning of the bench-top model devices at low and high pressuresDemonstrate a successful prototype of an active, electrochemical hydrogen barrier system within ahigh-pressure, polymer-lined, composite hydrogen storage tankAccomplishments Filed U.S. Patent Application on concept (# 10,253,265 in Sept. 2002)Negotiated and signed Cooperative Research and Development Agreement (CRADA) (No. 03-CR-07)with a major manufacturer of composite, high-pressure gas storage tanksFabricated initial tri-layer coatings, overcame wetting problems, and began electrical characterizationof the individual layers and tri-layersSynthesized Pt/Au nanoparticle catalyst that will be added into the poly-3,4-ethylenedioxythiophene(PEDOT) electrodes1

Hydrogen, Fuel Cells, and Infrastructure Technologies FY 2003 Progress ReportDesigned and built a low-pressure hydrogen permeability device at UCLADesigned a high-pressure hydrogen permeability device at INEELFuture Directions Test tri-layers on coupons of polymers within low-pressure permeability deviceConduct further electrical characterization of the tri-layersTest tri-layers with various catalysts at electrode interfaces using the low- pressure permeability deviceand select successful combinationsFabricate the high-pressure permeability deviceTest successful tri-layers on coupons within the high-pressure permeability deviceTest perfected tri-layers within commercial high-pressure composite gas storage tanksdeveloped. A schematic of this barrier is shownin Figure 1. The hydrogen partial pressureestablished by the voltage is extremely low atthe underlying polymer interface. The hydrogenpartial pressure can be calculated using theNernst equation, as shown in Figure 1. Anappropriate level of voltage will be calculatedand experimentally verified.IntroductionState-of-the-art high-pressure gas storage tanksconsist of an inner liner, made from a polymer suchas cross-linked polyethylene or nylon, overlaid witha continuous graphite fiber/epoxy reinforcementlayer. These tanks have successfully stored highpressure methane gas. It is desired to extend theapplication of this type of tank to high-pressurehydrogen. However, hydrogen has a significantlyhigher permeability rate through these polymer linersthan methane. Permeation not only leads to a gradualloss of hydrogen pressure, but the hydrogen isthought to damage and weaken the reinforcementlayer which could lead to cyclic fatigue or otherfailures of the tank.The development plan includes the following:1. The barrier is to be constructed of three layers ofpolymers consisting of a proton-conductingelectrolyte (electronic insulator) sandwiched inbetween electronically conductive polymerelectrodes. Candidate polymer compositions wereselected based upon existing knowledge. If thisThis project was recently begun to develop ahydrogen diffusion barrier that can be applied to theinterior of the polymer liner. The barrier will havethe following attributes: (1) low permeability ofhydrogen, (2) adhere well to the polymer liner, (3)stiffness (modulus) of the coating should match theunderlying polymer to avoid cracking when the tankis pressurized, (4) the application method shouldallow for coating inside a tank with a narrow neckand result in hermetic (gas-tight) coatings that aredevoid of pin-holes, (5) the material and coatingmethod should not appreciably add to the overall costor weight of the tank.ApproachAn electrochemically "active" hydrogenbarrier, fabricated from polymers, is beingFigure 1. Schematic Showing Tri-layer HydrogenBarrier Concept2

Hydrogen, Fuel Cells, and Infrastructure TechnologiesFY 2003 Progress Reportvoltage) characteristics of the device and compleximpedance measurements. Aluminum layers of 100nm thickness were evaporated on the two H-PEDOTlayers to form electrical contacts. I-V tests showedthat the device was a good electronic insulatorbecause of the insulating PAMPAS electrolyte. Thedevice showed a very low current ( 10-8 mA) underan applied bias (0-3 Volts), as shown in Figure 3.The complex impedance results will be reported inlater reports or papers.knowledge is not sufficient, new or modifiedcompositions will be developed. Appropriatecatalyst materials will be added at the electrolyte/electrode interfaces.2. The methods to manufacture the layers are beingadapted from existing techniques or developedduring the project. This could include dip coatingor spraying of monomers followed bypolymerization. Other possibilities will beexplored, and successful manufacturingtechnologies will be developed.Figure 4 shows the completed low-pressurepermeability apparatus. Figure 5 shows an initialpermeability test without a barrier and with a barrier(biased and unbiased). Significant reduction inpermeation was shown with addition of the tri-layer3. The device is designed as a galvanic-type devicethat functions to prevent hydrogen permeationthrough application of a small direct current (dc)voltage using small currents. Methods to provideattachment of the dc voltage are being developed.ResultsSignificant progress was made in all four taskareas: selection of materials, fabrication of tri-layercoatings, characterization of coating layers, andexperimental verification of hydrogenationprotection.The first set of candidate materials werefabricated as a tri-layer prototype barrier. Thematerial selected for the electrodes was highlyconductive H-PEDOT polymer (PEDOT a smallamount of alcohol). The addition of an alcohol (e.g.,ethylene glycol) has been shown to increase theelectronic conductivity of ordinary PEDOT by up tothree orders of magnitude. The material selected forthe electrolyte layer was PAMPAS [Poly (2acrylamino-2-methyl-1-propanesulfonic acid-costyrene)]. Tri-layers of these materials were firstmade by spin-coating on glass. Later, the layers werespin-coated on polymer substrates. However, thenon-polar surface of the PAMPAS electrolyteresulted in a high contact angle while spin-coatingthe second layer of PEDOT. To avoid this problem,the PAMPAS film was subjected to an ultravioletozone treatment to modify the surface. The contactangle was greatly reduced, and a good second layerof PEDOT was then obtained.Figure 2. Schematic of Fabricated Tri-layerElectrical characterizations were then conductedon the tri-layer devices shown as a schematicdiagram in Figure 2. These included I-V (current/Figure 3. I-V Characteristic Plot for the Tri-layerBarrier3

Hydrogen, Fuel Cells, and Infrastructure TechnologiesFY 2003 Progress ReportFigure 4. Low-pressure Hydrogen PermeabilityApparatus Fabricated at UCLAFigure 6. Cyclic Voltammetry of PEDOT Electrodesplus Pt/Au Nano-particles (Electrodes in 1 MHCl 1 M NaCl solution)PEDOT electrodes to enable the hydrogen reductionand oxidation reactions at the electrolyte interface,and additional hydrogen permeability tests will beconducted.Conclusions Figure 5. First Permeability Tests Using Low-PressureHydrogen barrier. However, there is little difference betweenthe biased and unbiased cases. Therefore, asprevious planned, a catalyst will be necessary (aswith proton exchange membrane type lowtemperature fuel cells) to enable hydrogen reduction/oxidation at the electrode/electrolyte interfaces. Platinum/gold (Pt/Au) is being investigated as acatalyst. This material was synthesized as nanoparticles in our laboratories. The material showsgood catalytic reduction of hydrogen as shown inFigure 6. The nano-catalyst will be incorporated into4Good progress has been made toward the finalgoal of developing a polymer liner that greatlylimits hydrogen losses from commercial, lightweight, composite, high-pressure hydrogentanks.All of the milestones that were set for this timeperiod have been achieved. Materials wereselected, and prototype tri-layer electrochemical barriers have been fabricated and characterized for electrical properties.Preliminary testing indicated that fine catalystparticles will be necessary at the electrode/electrolyte interfaces to reduce the high free energyof the hydrogen oxidation and reduction reactions.Nanoparticles of Pt/Au catalyst have been synthesized, and good catalytic reduction of hydrogen has been observed. Therefore, we are wellpositioned to test the tri-layer barriers (with catalyst) in the low-pressure permeability apparatus that was designed and fabricated.

Hydrogen, Fuel Cells, and Infrastructure TechnologiesFY 2003 Progress ReportFY 2003 Publications/PresentationsSpecial Recognitions & Awards/PatentsIssued1. “Low Permeation Liner for H2 Gas StorageTanks”, Paul A. Lessing, Y.Yang, L.P. Ma, F.C.Chen, V. Shrotriya, N. Sirosh, M.J. Warner,Hydrogen, Fuel Cells & InfrastructureTechnologies Program, 2003 Merit Review andPeer Evaluation Meeting, May 19-22, 2003,Berkeley, California.1. U.S. Patent Application: Paul A. Lessing,“Polymeric Hydrogen Diffusion Barrier, HighPressure Storage Tank so Equipped, Method ofFabricating a Storage Tank, and Method ofPreventing Hydrogen Diffusion”, September,2002.5

as cross-linked polyethylene or nylon, overlaid with a continuous graphite fiber/epoxy reinforcement layer. These tanks have successfully stored high-pressure methane gas. It is desired to extend the . permeability test without a barrier and with a barrier (biased and unbiased). Significant reduction in permeation was shown with addition of .