New LANL membrane bridges operational gap between low- and high-temperature PEM fuel cells; potential for lower cost systems
23 August 2016
A Los Alamos National Laboratory team, in collaboration with Yoong-Kee Choe at the National Institute of Advanced Industrial Science and Technology in Japan and Cy Fujimoto of Sandia National Laboratories, has discovered that fuel cells based on a new phosphate-quaternary ammonium ion-pair membrane can be operated between 80 °C and 200 °C with and without water, enhancing the fuel cells’ usability under a range of conditions. The research is published in the journal Nature Energy.
These fuel cells exhibit stable performance at 80–160 ˚C with a conductivity decay rate more than three orders of magnitude lower than that of a commercial high-temperature PEM fuel cell. By increasing the operational flexibility, this class of fuel cell can simplify the requirements for heat and water management, and potentially reduce the costs associated with the existing fully functional fuel cell systems.
Low-temperature PEM fuel cells that use Nafion are at present being commercialized in fuel cell vehicles, but these cells can operate only at relatively low temperatures and high hydration levels; therefore, they require humidified inlet streams and large radiators to dissipate waste heat. High-temperature PEM fuel cells that use phosphoric acid (PA)-doped polybenzimidazole (PBI) could address these issues, but these PBI-based cells are difficult to operate below 140 ˚C without suffering loss of PA. The limited operating temperature range makes them unsuitable for automotive applications, where water condensation from frequent cold start-ups and oxygen reduction reactions at the fuel cell cathode occur during normal vehicle drive cycles.
In this work, we demonstrate that fuel cells based on quaternary ammonium (QA)-biphosphate ion-pair-coordinated polyphenylene (PA-doped QAPOH) PEMs can avoid the limitations of Nafion and PBI-based fuel cells, enabling operation under a wide range of conditions that are off-limits for existing fuel cell technology. These PEMs can conduct protons through stable ionic pair complexes and enable fuel cell operation at temperatures from 80 to 180 ˚C.—Lee et al.
Currently, two main classes of polymer-based fuel cells exist. One is the class of low-temperature fuel cells that require water for proton conduction and cannot operate above 100 °C. The other type is high-temperature fuel cells that can operate up to 180 °C without water; however, the performance degrades under water-absorbing conditions below 140 °C.
There’s a huge benefit to running fuel cells at the widest possible operating temperature with water tolerance. But current fuel-cell vehicles need humidified inlet streams and large radiators to dissipate waste heat, which can increase the fuel-cell system cost substantially, so people have looked for materials that can conduct protons under flexible operating conditions. It is very exciting that we have now found such materials.—Yu Seung Kim, the project leader at Los Alamos
The operating temperature window of a PEM fuel cell is determined by the interactions between the acid (for example, tethered sulfonic acid or free phosphoric acid) and the base moieties (for example, free water or tethered QA) in the membrane, the researchers explained.
For low-temperature fuel cells, the hydrogen bonding interactions between the sulfonic acid group and water molecules in Nafion is only 15.4 kcal mol−1; this does not provide enough stability above the boiling temperature of water, leading to membrane dehydration.
For high-temperature fuel cells, The intermolecular interaction energy between benzimidazole and PA is 17.4 kcal mol−1—only 4.8 kcal mol−1 greater than that between PA and one water molecule, about 12.6 kcal mol−1. Due to the relatively weak interaction, benzimidazole tends to lose PA easily with water absorption. PA-doped PBI requires a high concentration of base moieties and a high acid content to impart sufficient anhydrous conductivity.
The research team found that a phosphate-quaternary ammonium ion-pair that has much stronger interaction, which allows the transport of protons effectively even under water-condensing conditions.
The discovery happened when we were investigating alkaline hydroxide conducting membranes, which have quaternary ammonium groups. While the alkaline membranes work only under high pH conditions, the idea came across that alkaline membranes can be used under low pH conditions by combining with phosphoric acid. This was a breathtaking moment, when Choe brought the calculation data that showed the interaction between quaternary ammonium and biphosphate is 8.7 times stronger than conventional acid-base interaction.—Yu Seung Kim
The Los Alamos team collaborated with Fujimoto at Sandia to prepare quaternary ammonium functionalized polymers. The prototype fuel cells made from the ion-pair-coordinated membrane demonstrated excellent fuel-cell performance and durability at 80-200 °C, which is unattainable with existing fuel cell technology.
The performance and durability of this new class of fuel cells could even be further improved by high-performing electrode materials, said Kim, citing an advance expected within five to ten years that is another critical step to replace current low-temperature fuel cells used in vehicle and stationary applications.
Researchers on this project include Kwan-Soo Lee (Los Alamos National Laboratory, Chemistry Division), Jacob Spendelow, Yu Seung Kim (Los Alamos National Laboratory, Materials Physics and Applications Division), Yoong-Kee Choe (National Institute of Advanced Industrial Science & Technology, Japan), and Cy Fujimoto (Sandia National Laboratories).
Los Alamos has been a leader in fuel-cell research since the 1970s. Fuel cell technologies can significantly benefit the nation’s energy security, the environment and economy through reduced oil consumption, greenhouse gas emissions, and air pollution. The current research work supports the Laboratory’s missions related to energy security and materials for the future.
Kwan-Soo Lee, Jacob S. Spendelow, Yoong-Kee Choe, Cy Fujimoto & Yu Seung Kim (2016) “An operationally flexible fuel cell based on quaternary ammonium-biphosphate ion pairs” Nature Energy 1, Article number: 16120 doi: 10.1038/nenergy.2016.120
This is a major discovery for near future low temperature fuel cells with improved temperature bracket operation, longer live and probably much lower mass produced cost.
Could become the improved FC required for all weather vehicles by 2020/2022 or so?
FCs are not dead. More versions will soon be discovered.
Posted by: HarveyD | 23 August 2016 at 12:07 PM
So a pink unicorn can be mated with a green unicorn and you get....striped unicorns! Now we just have to put together a national distribution network of unicorn food and we're all set!!!
Posted by: DaveD | 23 August 2016 at 05:48 PM
From my past posts some here might think me anti-fuel cell. This is untrue, I simply believe you should use the right tool for the right job and for ~95% of lite duty vehicle use a battery electric works just fine. But what about heavy duty? Fuel cells would be great for long haul trucking, buses, or just going on a family vacation in a RV/towing your boat trailer.
Posted by: ai_vin | 24 August 2016 at 05:05 AM
You bring up a good point. For long haul trucking, trains, etc. I have no problem considering Fuel Cells as a viable alternative. Batteries are not practical and you don't have to develop nearly the infrastructure for trains or even long haul trucking to be viable.
The one thing that still scares me here is the amount of hydrogen it would take and the pressure it would be under to power big rigs or trains. There will come a day where some idiot, somewhere, finds a way to do something stupid and set off an explosion. That energy would be incredible. Petrol or diesel just burns and has a hard time getting nearly the explosion so it is just simply a different thing to contend with.
Posted by: DaveD | 24 August 2016 at 09:26 AM
NG and Propane are as explosive and they are in use in most US homes (+ offices) for the last century and more.
Near future (NISSAN) biofuel FCs may solve the compression, storage and transportation problems claimed to be related to H2.
Posted by: HarveyD | 26 August 2016 at 11:45 AM
Well Dave, one way around that is to use Liquid Organic Hydrogen Carriers (LOHC). LOHCs store more H2 per volume that even 700 bar H2 gas, but you can hold it in a plastic milk jug. The problem with using it you need more than just a tank, you need some extra equipment to get the LOHC to release the H2. This could be a show stopper for small vehicles like cars but not big ones like trains, trucks, or boats.
Posted by: ai_vin | 29 August 2016 at 07:41 AM