National Science Foundation     |     Directorate for Engineering  (ENG)
Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)
CBET Award Achievements (Nuggets)
Notable Accomplishments from CBET Awards
Advanced Ceramic-based Electrolyte Materials for Hydrogen Fuel Cells
Juan Nino  –  University of Florida

Background:  In the search for intermediate-temperature proton conducting electrolytes for hydrogen fuel cells, phosphate-based materials have been proposed as a solution that can bridge the performance gap between low-temperature polymer-based electrolytes and high-temperature oxide ceramics.  However, the research on phosphates has been limited to mainly the two structurally simplest type of compounds i.e. the orthophosphates/monophosphates and pyrophosphates.  Therefore, the vast domain of complex phosphates (e.g.: cyclophosphates, ultraphosphates, metaphosphates, and oligophosphates) is virtually unexplored.  To address this, this project investigates the influence of crystal structure on the proton conductivity across the family of complex Lanthanum phosphate compounds.  Since the main difference between these phosphates is the degree of interlinking between the neighboring PO4 tetrahedra, these compounds represent an ideal scenario and test case for identifying structure-protonic conductivity relationships.

Results:  A literature and crystallography review of the variety of complex structures across the phosphate family of compounds was performed.  Model crystal structures for all the compounds within this family of materials were built in CrystalMakerTM and are now available for consultation by the scientific community.  Compilations of all relevant crystal structures are shown in the Figures below.  The fundamental structural unit common to all phosphates is the PO4 tetrahedron.  Monophosphates or orthophosphates are structurally the simplest type of phosphates consisting of isolated PO4 tetrahedrons.  Each PO4 tetrahedron can share one or more of its oxygen ions with neighboring tetrahedra to produce more complex phosphates.  Metaphosphates and Ultraphosphates consist of infinitely long chains or sheets or 3D structures of linked PO4 tetrahedra.  Such materials hold promise as the continuously linked tetrahedra can provide conduction pathways for transport of charge within these structures leading to extremely high conductivity.  Protons move within a proton conducting material via the Grötthuss mechanism which involves proton hopping between neighboring oxygen ions.  Continuously linked tetrahedra of PO4 essentially provide an obstructionless expressway for the transport of protons through the structure.  The significant differences between the different categories of phosphates are shown in the table below along with their respective crystal structures.

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Figure 1.  Crystal structure of LaPO4 consisting of isolated tetrahedra of (PO4)3- (green).  The tetrahedra are separated by cations (La3+, yellow).  View along the x-axis (left) and view on the z-axis (right).

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Figure 2.  Crystal structure of La2P4O13 which is a tetraphosphate (Oligophosphates, n=4).  The structure consists of quartets of PO4 tetrahedra which are separated from each other by positively charged cations (purple).  Corner sharing LaO8 dodecahedra (purple) separate neighboring quartets of PO4 tetrahedra.

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Figure 3.  Crystal structure of La(PO3)3 (Lanthanum metaphosphate) showing continuously linked PO4 tetrahedra (green) along the z-axis.  The individual chains of PO4 tetrahedra form a helical structural with its axis along the z-axis.  Orange polyhedral show the LaO8 'dodecahedra'.  (Right) Crystal structure of La (PO3)3 as seen along the z-axis.  Four distinct helixes of infinitely linked PO4 tetrahedra can be clearly seen.

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Figure 4.  Crystal structure of LaP5O14 as seen in the z-y plane (left).  The PO4 tetrahedra (blue) are linked to form an infinitely long ribbon.  Overall structure consists of multiple ribbons stacked together and separated by cations.  (Right) Crystal structure as seen in the x-y plane showing the individual ribbons stacked on top of each other.  Note the individual ribbons are separated by cations (La3+, purple) to balance for the negative charge of the anion.

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Figure 5.  Young engineering enthusiasts participating in Engineers Extravaganza (part of E-Week 2008) held at the University of Florida.

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Figure 6.  Participants at the MSE Teach workshop getting hands on experience with some of the experimental techniques.
Credit for Images 1 thru 6:  Satyajit Phadke and Juan C. Nino, Materials Science and Engineering, University of Florida
This project addresses the NSF Strategic Outcome Goals, as described in the NSF Strategic Plan 2006-2011, as follows:
Primary Strategic Outcome Goal:        (1) Discovery:  The project's goal is to identify structure-property relationships by means of a systematic investigation of proton conductivity properties of a large variety of structurally diverse compounds in the family of lanthanum phosphate compounds.  Also, in the process, a deeper understanding of the proton conduction mechanisms is expected, which can further direct future research in the field.
                                                                     (1) Discovery Category:
                                                                            - Engineering Research
                                                                            - Mathematical & Physical Sciences

Secondary Strategic Outcome Goals:  (2) Learning and Research Infrastructure:  By participating in activities such as Engineers Extravaganza and MSE Teach 08 the project contributes to the dissemination of information about alternative and sustainable energy sources among a wide variety of audiences that includes K-12 students, teachers and the general public.  New electrolyte materials generated by this research could impact research activities on solid oxide fuel cells by others around the world.
                                                                     (2) Learning and Research Infrastructure Categories:
                                                                            - K-12 Education
                                                                            - Undergraduate Education and Undergraduate Student Research
                                                                            - Graduate Education and Graduate Student Research
                                                                            - Broadening Participation to Improve Workforce Development
                                                                            - Research Resources (minor facilities, infrastructure and instrumentation,
                                                                                  field stations, museum collections, etc.)

Scientific Uniqueness:  The systematic crystallographic variations within the family of complex lanthanum phosphate compounds offers and ideal scenario for investigating the influence of crystal structure on the proton conductivity and identifying relevant structure property relationships towards the development of intermediate-temperature proton conducting compounds.

In terms of Intellectual Merit, this work is notable because this research could lead to electrolyte materials that will allow solid oxide fuel cells to operate at lower temperatures, which would greatly simplify the complexities of this fuel cell system and help accelerate the deployment of this technology.

In terms of Broader Impacts, this work is notable because the deployment of solid oxide fuel cells, which could operate on hydrocarbon fuels directly, will have a significant impact on the electrical power industry in this country and around the world.  The PI's extensive outreach activities will help recruit more under-represented groups into science and engineering fields.

Additional Broader Impact Results:  (1Engineers Extravaganza:  The PI, along with his student, put up a poster and model display at the Engineering Extravaganza, a local showcase of projects and demonstrations open to the general public as part of the yearly Engineers Week activities in Gainesville, Florida.  The mission of this event is to educate university students, local primary-education students, alumni, and the general public about the achievements of all engineering disciplines and their practical applications in society.  The display showcased a poster on the causes and effects of global warming and an overview of the diverse research being done at the University of Florida to develop viable alternative energy sources.  Another displayed item focused on Hydrogen Fuel Cells, explaining the basics of the technology in layman's terms, and also showcasing the research being done within the group in this field.  Two prototype models of operational hydrogen fuel cell cars owned by the group for demonstration purposes were also a part of the display.  The majority of the audience for this event was middle school and high school students accompanied by their parents.
                                                              (2MSE Teach 08:  The PI took part in an annual event, MSE Teach 08, hosted by the Department of Materials Science and Engineering at the University of Florida.  This event was attended by 15 science teachers from neighboring counties who teach at the K-12 level.  In the short workshop the participants were introduced to the diverse range of properties that ceramic materials exhibit.  Also, the emphasis was on presenting the broad (yet typically unacknowledged) use of ceramic materials in every day applications and commonplace devices.  The participant teachers were also provided with teaching materials by the PI that they can use in their classrooms to increase awareness among the students at K-12 level.

This research is Transformative.  This research represents a stepping stone towards what is expected to be the determination of key structure-proton conduction relationships that can transform the way these types of materials are being designed, tailored and engineered for hydrogen fuel cell use.

This research represents Broadening Participation.  By participating in programs like MSE Teach 08 and Engineers Extravaganza as a part of the project as described above, students K-12, their teachers and the community in general are being both spectators and active participants in this project.

Existing or potential Societal Benefits of this research:  The project has a number of benefits to the US economy and society:
      *  The research focuses on development of materials that will enable the development of alternative, clean and sustainable energy sources.
      *  Also by taking part in a number of public activities, the project helps to enhance public awareness of research to develop clean energy sources.  Also, it serves to educate the next generation about the exciting opportunities available in this field.

Program Director:
Trung Van Nguyen
CBET Program Director - Energy for Sustainability
NSF Award Number:   0730900
Award Title:
  Advanced Ceramics for Intermediate-Temperature Proton Conducting Membranes
PI Name:   Juan Nino
Institution Name:   University of Florida
Program Element Code:   7644
NSF Investments:
  - American Competitiveness Initiative (ACI)
- Climate Change
- Cyber-enabled Discovery and Innovation
- Sensor Research
- Environment (including the importance of fresh water and dynamics of water processes)
CBET Nugget:

  FY 2009

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This Nugget was Updated on 8 October 2009.