Proton Conduction and Oxygen Diffusion in Ultra-Thin Nafion Films in PEM Fuel Cell: How Thin?
The success of PEM fuel cells lies in the design of the cathode where C-supported Pt catalyst is covered by a thin layer of ionomer, allowing easy access of oxygen and protons. The high current densities (1-2 A/cm2) are achieved by the optimization of the thickness of the ionomer between two opposing trends: thinner ionomer allows high oxygen through-plane diffusion, while the in-plane conduction of the protons requires reasonable thickness. Anisotropy is likely to develop in such thin films. The purpose of this work was to investigate the effect of a thinner ionomer layer on the diffusion and conductivity and to establish how thin the ionomer layer can be. Oxygen permeability (DH) and proton conductivity in ultra-thin Nafion films (100-1000nm) were respectively characterized on SiO2 substrate via limiting current measurement and electrochemical impedance spectroscopy for a range of temperature and relative humidity conditions. The transport behavior of these films is comparable to the electrode membrane layer of PEM fuel cells. Values of oxygen permeability were shown to increase with decreasing film thickness. The oxygen diffusion through the gas boundary layer becomes significant only at ultra-thin film thickness. The proton conductivity decreases with decreasing thickness and was disproportional to bulk Nafion behavior. Post-test SEM imaging shows buckling of the thin layer on the silicon wafer between the Pt sites, partially explaining the opposing trends in diffusivity and conductivity as film thickness decreases. Anisotropy exists as the thickness becomes comparable to the size of the aqueous regions of the Nafion ionomer. Measurements of thinner layers (<100nm) were experimentally limited, yet the trends indicate that the thinness of the ionomer in the cathode is limited by its ability to allow proton conductance.
- Research Organization:
- General Motors LLC, Detroit, MI (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE)
- Grant/Contract Number:
- EE0000470
- OSTI ID:
- 1613261
- Journal Information:
- Journal of the Electrochemical Society, Vol. 166, Issue 2; ISSN 0013-4651
- Publisher:
- IOP Publishing - The Electrochemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Recycling of Proximity Binding-Based DNA Architecture Driven by Hairpin Strand Displacement for Amplified Electrochemical Aptasensor
|
journal | January 2019 |
Similar Records
Surface-Directed Fabrication of Integrated Membrane-Electrode Interfaces
Novel Fluorinated Ionomer for PEM Fuel Cells SBIR Phase I Final Scientific / Technical Report Period Covering April 9, 2018 to January 8, 2019