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Final Report: Capstone Senior Design - Supramolecular Proton Exchange Membranes for Fuel Cells
EPA Grant Number: SU831899Title: Capstone Senior Design - Supramolecular Proton Exchange Membranes for Fuel Cells
Investigators: Fuchs, Alan , Gecol, Hatice , Whiting, Wallace
Institution: University of Nevada - Reno
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: September 30, 2004 through May 30, 2005
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity, and the Planet (2004)
Research Category: Pollution Prevention/Sustainable Development
Description:
Objective:The ultimate aim of the project is to investigate the effect of surfactants and supramolecular chemistry on the proton conductivity of the PBI membrane. The scope of this project focuses mainly on the synthesis and characterization of PBI membrane, but also includes environmental considerations for the entire fuel cell process. First, pristine PBI must be synthesized. Next, the membrane must be functionalized by various methods such as acid doping. The characterization primarily involves the proton conductivity of the membrane, but also includes acid doping levels, PBI structure, supramolecular structure, mechanical and thermal properties. However, due to the timeframe of the project, the semester long senior design project’s scope was to accomplish as much as possible while recognizing that much more work and time is required for a successful project. Thus, the purpose of this project's to help establish proper infrastructure and knowledge to facilitate future research at the University of Nevada, Reno. Issues regarding PBI synthesis and modeling, dissolving PBI powder, casting a membrane, FT-IR characterization, and measuring proton conductivity were investigated. Nafion®, the commercially used PEM, was also characterized to form a basis of comparison, as well as help to learn impedance spectroscopy techniques. A basic analysis of the life cycle, using the program GREET was used.
Summary/Accomplishments (Outputs/Outcomes):Two batches of PBI polymer were synthesized and the identity of the first batch was confirmed using FT-JR spectroscopy. A 4-probe conductivity cell has been constructed and used for AC impedance spectroscopy. Nafion® was obtained, treated, and the conductivity was measured using 4-probe impedance spectroscopy as a basis for comparison to PBI. The conductivity of Nafion® at room temperature was found to be 0.092 and 0.087 S/cm for Nafion® 115 and 112, respectively. Several methods were employed to cast a PBI membrane. The most prevalent solvent for casting PBI membranes found in literature is dimethyl acetamide (DM4c)5, s this was the initial solvent used. However, even at temperatures as high as 170 °C, 4nly a very small amount of PBI dissolved. The amount dissolved was insufficient to cast a membrane.
Repeated casting of the dilute solution onto a slide did not produce a thick enough layer of polymer. Another method found in literature that utilizes a different solvent was also investigated. The solvent used is trifluoroacetic acid (TFA). The doping agent in this case is added directly to the solution before casting. This solvent was much more efficient at dissolving the PBI than DMAc. However, the previoi4s casting method was insufficient for this particular solvent and new methods are currently being studied.
A “well to wheel” life-cycle analysis was conducted on passenger vehicles using conventional gasoline, biodiesel, and hydrogen fuel cells. Theses fuel sources were chosen due to their importance in the city of Reno: (1) the University of Nevada’s fleet of vehicles runs on BD2O (20% biodiesel, 80% petroleum diesel), (2) conventional gasoline sold in Reno, and (3) fuel cell technology. The model used to conduct this analysis was GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) a Microsoft® Excel based program created by Argonne National Laboratories at the University of Chicago. The model suggests that fuel cell vehicles require 32-34% less total energy to use than either BD2O vehicles or gasoline powered vehicles. PM1O is the only criteria pollutant released by a hydrogen powered fuel cell vehicle and fuel cell vehicles release between 42-49% less PM1O than the other two vehicle types.
Conclusions:
A 4-probe conductivity cell has been constructed and used for AC impedance
spectroscopy. Nafion has been obtained, treated, and tested to give conductivity
values comparable to literature. PBI powder has been synthesized and characterized by FT-IR.
The conductivity results from Nafion® suggest that membrane thickness has
little influence on membrane conductivity. Therefore when a PBI membrane is
cast, no optimum membrane thickness will be pursued.
The GREET model results suggest the fuel cell vehicle are an environmentally friendly solution to greenhouse gas emissions, however, other issues related to the development of a hydrogen economy must be resolved before the full impact of fuel cell vehicle use can be analyzed.
Work on the PBI membrane is about halfway completed. Many of the experimental procedures necessary for research have been developed, although more work is still required. Establishing the experimental procedures has proved to be a substantial obstacle in order to accomplish important experimental results. The lack of certain infrastructure has also somewhat slowed the research. In order to fulfill the project’s objectives, more results and will be obtained before the P3 competition. For future work, PBI powder still needs to be dissolved in a solvent, cast as a membrane, and functionalized with acid doping and supramolecular chemistry. With a successful casting procedure, a doped membrane may also be tested before the final presentation. After establishing these experimental procedures, the effects of surfactants and supramolecular chemistry can also be investigated and characterized. This is the ultimate goal for the project, which hasn’t yet been achieved. More time is needed to obtain these results.
Proposed Phase II Objective and Strategies
Task 1: Education of Students about Supramolecular Nanocomposites based on poly (1-BI) and inorganic ionic conductors. Supramolecular PBI polymer blends will be prepared to improve the strength and flexibility of the member. Blends of PBI and polyetherimide will be investigated since they form hydrogen bonded supramolecular systems. In addition, acid doped PBI / poly (4VP) also form miscible blends due to hydrogen bonding (Cho et.al., 2001 and Pu, 2003). It is believed hat the incorporation of supramolecular structure into the PEM can bring channels and pores into the membrane to facilitate proton transport.
Task 2: Pedagogical Issues Related to Characterization of he Nanocomposite Supramolecular PEM. Characterization of the supramolecular nanocomposite membranes will be done by: proton conductivity, atomic force microscopy, SEM and thermal analysis.
Task 3: Educational Issues Related to Membrane Durability - Chemical, Electromechanical and Mechanical Stability of Supramolecular Nanocomposite PEM’s. There are a variety of challenges relating to: chemical, electrochemical and mechanical stability. Here is a summary of those challenges: 1) Chemical -The main issue here relates to methanol exposure and crossover. Methanol resistance frill be investigated by testing performance before and after exposure. 2) Electrochemical - The main issues relate to catalyst poisoning and membrane electrode materials. We propose to measure proton conductivity as a measure of this stability. 3) Mechanical - Characterization of static and dynamic mechanical properties including brittleness, tensile modulus, storage and loss modulus.
Task 4: Lifecycle Analysis of PEM Fuel Cell. Lifecycle analysis is an essential feature connecting the novel fuel cell membrane technology to P issues. For this project, involving small appliance power devices, the connection involve a comparison between natural gas / hydrogen / fuel cell / electricity or methanol / fuel cell / electricity with coal / electricity / rechargeable battery / electricity. This lifecycle analysis will compare environmental impact and cost for cradle to grave.
Supplemental Keywords:fuel cell, proton exchange membrane, Polybenzimidazole,
PBI, PEMFC, hydrogen, supramolecular chemistry, AC impedance spectroscopy, proton conductivity,
,
INTERNATIONAL COOPERATION, TREATMENT/CONTROL, Sustainable Industry/Business, Scientific Discipline, RFA, Technology for Sustainable Environment, Sustainable Environment, Chemical Engineering, Technology, Environmental Engineering, Environmental Chemistry, pollution prevention, environmental sustainability, proton exchange membrane fuel cell (PEMFC), cleaner production, clean technologies, engineering, alternative products, alternative energy source, fuel cell energy systems, energy storage options, energy technology
Progress and Final Reports:
Original Abstract