Hydrogen fuel cell technology provides a new insight for clean-energy methods that can help reduce pollution and greenhouse emissions. Specifically, electricity is generated through a chemical reaction between hydrogen and oxygen, in which only water and heat are produced. The improvement of their performance relies on the development of better materials to effectively transport ions.
A fuel cell consists of three main components: an anode (negative electrode), a cathode (positive electrode), and an ion-conducting membrane in the middle. The membrane allows ions to flow between the electrodes; however, the efficiency of the process depends on the membrane’s permeability. Previous fuel cell technologies have focused on proton exchange membranes, which require expensive catalysts to continue chemical reactions. An alternative includes anion exchange membranes, and the reactions that occur within the electrodes can be activated with less expensive catalysts, such as iron or nickel. On the contrary, anion exchange membranes cannot transport ions as effectively as proton exchange membranes.
To combat the challenge, Assistant Professor Benjamin Paren, who studies fuel cells at Stevens Department of Chemical Engineering and Materials Science, has collaborated with Professor of Chemistry Chulsung Bae at Rensselaer Polytechnic Institute. Professor Bae is an expert at synthesizing polymer membranes, and Paren’s team could investigate how the molecular structure of polymer membranes affects their performance. The research consisted of focusing on how water affected the organization of polymers and the ability to create pathways for ions to travel through membranes.
The membrane performance relies on how quickly ions can transport through it and is influenced by the membrane’s polymer structure. One of the most unexpected results involved the behavior of rigid polymers. Stiffer polymers are commonly known to restrict ion movement, while flexible ones can adjust to create more uniform channels for ions to flow faster. However, when certain rigid polymers were exposed to water, they formed well-defined channels. “Usually, membranes that are stiffer or more rigid don’t allow ions to move as quickly. But what was exciting is when we introduced water, we found that even the polymers that were more rigid when they were dry became a lot more flexible. And it allows ions to rearrange in channels,” explained Professor Paren.
Additionally, Paren’s team examined the membranes’ nanoscale structures utilizing X-ray scattering, a method for studying the arrangement of materials at the microscale. Paren elaborates that “It’s really important to test things under the conditions that you’ll be using them in,” to understand the performance under realistic operations. The team is continuing to research how varying humidity levels can affect ion movement, conductivity, and the nanoscale structure of membranes. The discovery demonstrated that well-defined and organized channels within hydrated polymers offer promising insight for the support of efficient ion transport.
The research was published in the journal Macromolecules and has demonstrated the importance of evaluating membranes in their hydrated, working state. Furthermore, it has revealed how a material’s performance can change dramatically under real operating conditions. The application of hydrogen fuel cells can benefit electrolyzers, which split water molecules into hydrogen and oxygen. Energy produced by renewable sources, such as wind or solar power, can be utilized to produce hydrogen through electrolyzers. In return, the hydrogen can be stored until it is later needed and converted back into electricity by fuel cells. Paren expressed, “It is an important step forward for the field that hopefully others working on similar systems will be able to build off of as well.”
