Novel proton-conductive membranes for automobile fuel cells
by Riko Saibo
Tokyo, Japan (SPX) Aug 06, 2023
In the evolving world of electric vehicles (EVs), fuel cells play a pivotal role. Acting as compact energy conversion units, they leverage clean hydrogen energy, turning it into electricity via oxidation-reduction reactions. One of the critical components in these cells is the proton-conductive membrane, a vital aspect of proton exchange membrane fuel cells (PEMFCs). These membranes, while essential, often suffer from a compromise between durability and ion conductivity, impacting the PEMFC’s lifespan and efficiency.
For years, the industry has witnessed attempts to better these membranes. Several modified versions like Nafion HP, Nafion XL, and Gore-Select were produced, offering more durability than the conventional ones used in fuel cells. But a significant challenge remained. The U.S. Department of Energy (DOE) had set a benchmark: for these membranes to be viable for automotive fuel cells by 2025, they had to pass an accelerated durability test, combining chemical and mechanical assessments. So far, none have hit the mark.
This was the landscape until a team of Japanese researchers, helmed by Professor Kenji Miyatake of Waseda University and the University of Yamanashi, presented a groundbreaking solution. Collaborating with Dr. Liu Fanghua of the same institutions and Dr. Ick Soo Kim from Shinshu University, they unveiled their work in the journal Science Advances.
The team’s approach hinged on crafting proton-conductive membranes from a partially fluorinated aromatic ionomer termed SPP-TFP-4.0. This ionomer was reinforced using the push-coating method with either high porosity PVDF nanofibers or porous ePTFE. The outcome? Composite membranes, SPP-TFP-4.0-PVDF and SPP-TFP-4.0-ePTFE, with thicknesses of 14 and 16 um, respectively.
Extensive tests on these membranes revealed the one bolstered with PVDF stood out. Miyatake emphasized, “It outperformed the state-of-the-art chemically stabilized and physically reinforced perfluorinated Nafion XL membrane in terms of fuel-cell operation and in situ chemical stability at a high temperature of 120oC and a low relative humidity of 30%.”
Its longevity is noteworthy: 148,870 cycles or 703 hours in accelerated durability tests, surpassing the DOE target by over sevenfold. It also showcased commendable chemical stability, consistent rupture energy across humidity levels, dependable mechanical properties, and exemplary fuel-cell performance at higher temperatures.
The implications of this development are substantial. Meeting the U.S. DOE’s criteria for future automotive fuel cells means this innovative aromatic polymer-based proton-conductive membrane could be the sought-after alternative. This paves the way for fuel cells that operate at higher temperatures and have increased longevity.
Looking at the broader picture, Miyatake concluded, “As a result, fuel cell-based electric vehicles may become more powerful and affordable. This would also contribute towards realizing a hydrogen-based, carbon-free society.”