Advancing ionomer design to boost interfacial and thin-film proton conductivity via styrene-calix[4]arene-based ionomers

• Published in: Cell reports physical science Vol. 4; no. 2; p. 101282
• Main Authors: Chatterjee, Shyambo, Obewhere, Oghenetega Allen, Zamani, Ehsan, Keloth, Rajesh, Farzin, Seefat, Morton, Martha D., Sarella, Anandakumar, Dishari, Shudipto Konika
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.02.2023; Elsevier
• Subjects: calixarene; Chemistry; Energy & Fuels; energy conversion and storage devices; fuel cell; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; interface; ion transport limitation; ionomer; macrocycle; Materials Science; Physics; polymer; proton conductivity; thin film; polymer; ion transport limitation; fuel cell; ionomer; macrocycle; thin film; energy conversion and storage devices; proton conductivity; interface; calixarene
• ISSN: 2666-3864; 2666-3864
• DOI: 10.1016/j.xcrp.2023.101282

Sub-micrometer-thick ion-conducting polymer (ionomer) layers often suffer from poor ionic conductivity at the substrate/catalyst interface. The weak proton conductivity makes the electrochemical reaction at the cathode of proton-exchange-membrane fuel cells sluggish. To address this, here we report on a class of polystyrene-based ionomers having sub-nanometer-sized, sulfonated macrocyclic calix[4]arene-based pendants (PS-calix). In films with thickness comparable to that of ionomer-based binder layers, the conductivity of PS-calix film (∼41 mS/cm) is ∼13 times higher than that of the current state-of-the-art ionomer, Nafion. We observe a similar improvement in proton conductivity when PS-calix interfaces with Pt nanoparticles, demonstrating the potential of PS-calix in catalyst ink. Leveraging a favorable interfacial chemical composition, PS-calix enhances proton conduction at the film-substrate interface, a shortcoming of Nafion. Moreover, the water in PS-calix films diffuses faster than bulk water and the water confined in Nafion films, suggesting an important role played by sub-nanometer-sized calix[4]arene cavities in creating unique water/ion transport pathways. [Display omitted] •A class of ionomer (PS-calix) leveraging sub-nanometer-sized cavities of calix[4]arene•PS-calix exhibits proton conductivity ∼13 times higher than Nafion in thin films•Fast proton conduction is facilitated by faster-than-bulk water transport•Alleviates ion and gas transport limitations, desired for binders for fuel cells Chatterjee et al. incorporate sub-nanometer-sized macrocyclic cavities within the chemical structure of ionomers. This class of ionomer exceeds the water and proton transport performances of the state-of-the-art ionomer Nafion in thin materials, mimicking catalyst-binder layers of fuel cell electrodes.