Mixed Anion Chalcogenides for Proton Conducting Membranes
Document information
| Author | Steven A. Poling |
| School | Iowa State University |
| Major | Materials Science and Engineering |
| Year of publication | 2006 |
| Company | Iowa State University Research Foundation, Inc. |
| Document type | Patent |
| Language | English |
| Format | |
| Size | 1.64 MB |
Summary
I.Novel Proton Conducting Membranes for Hydrogen Oxygen Fuel Cells
This research introduces new mixed anion-based compounds suitable for proton exchange membranes. These materials can operate over various temperatures, including the intermediate range of 100°C to 300°C. Notably, crystalline mixed anion chalcogenide compounds can also be utilized in such membranes.
1. Importance of Proton Exchange Membranes for Fuel Cells
Proton Exchange Membranes (PEMs) are crucial components of hydrogen-oxygen fuel cells, enabling the transport of protons while electrically insulating the anode and cathode. This process generates electricity with water as a byproduct, making it an environmentally sustainable technology.
2. Challenges in Proton Exchange Membranes
Existing PEMs face limitations in operating temperature range, particularly in the intermediate range of 100°C to 300°C. This hinders their application in fuel cells that could optimize performance.
3. Novel Proton Conducting Materials and Compounds
To address these challenges, the research team has developed novel materials and compounds for PEMs that exhibit proton conductivity in the desired temperature range. These materials are amorphous, crystalline, or mixed phase with structural protons and exhibit proton conductivity ranging from 10^-8 S/cm to 10^-1 S/cm between -60°C and 300°C at varying relative humidities.
4. Synthesis and Characterization of Proton Conducting Materials
Protonated compounds were synthesized via aqueous mixtures of starting materials, with crystalline compounds obtained at room temperature using excessive acetone. Amorphous compounds were produced by slow heating the solution, allowing for controlled evaporation. Structural characterization employed techniques like IR, Raman spectroscopy, DSC, TGA, and X-ray diffraction.
5. Potential Applications in Fuel Cells
The proton conducting materials show promise for use in proton exchange membranes of hydrogen-oxygen fuel cells, offering the potential to operate in a wider temperature range, including the intermediate range of 100°C to 300°C. This could lead to optimum fuel cell performance and broader applicability.
II.Material Properties
The developed materials exhibit proton conductivity ranging from 10−8 S/cm to 10−1 S/cm within a temperature range of −60°C to 300°C and a relative humidity below 12%. They can exist in amorphous, partially crystalline, or mixed phase structures with incorporated protons.
III.Material Synthesis
Protonated compounds can be obtained from aqueous mixtures of starting materials. Crystalline proton conducting compounds can be produced at room temperature by adding excessive acetone to the solution. Slow heating of the solution allows for the formation of amorphous proton conducting materials.
IV.Applications in Proton Exchange Membranes
Crystalline sodium thio-hydroxogermanate compounds, specifically Na3GeS3(OH)8⋅8H2O and Na2GeS2(OH)2⋅5H2O, have been successfully utilized in proton conducting membranes.
V.Implications for Fuel Cell Technology
These novel proton conducting membranes have the potential to advance hydrogen-oxygen fuel cells by enabling efficient operation in the intermediate temperature range of 100°C to 300°C. This range is crucial for reducing the reliance on expensive platinum catalysts and mitigating fuel cross-over issues.
1. Proton Exchange Membranes for Fuel Cells
Polymer exchange membranes are popular electrolyte materials used in fuel cells, but they require hydration to maintain high proton conductivity, limiting their operation below 100°C and requiring expensive noble metal catalysts like platinum. Phosphoric acid membranes operate between 150°C and 200°C but suffer from membrane leakage and fuel cross-over issues. Solid oxide membranes, used between 700°C and 1000°C, can reduce platinum usage but pose challenges in achieving the desired oxide anion conductivity. However, there exists a temperature gap between 100°C and 300°C for which no suitable membrane is currently available.