The innovation engine for new materials

Alejandra Acosta-Hernandez

Alejandra Acosta-Hernandez, Chemistry, University of California Santa Barbara

Major: 

Chemistry

Mentor(s): 

Austin Barnes

Faculty Sponsor(s): 

Steven K. Buratto

Faculty Sponsor's Department(s): 

Chemistry and Biochemistry

Project Title: 

Mapping the Hydrophilic Channels of a Nafion-like Anion Exchange Membrane

Project Description: 

Fuel cells are an efficient high power alternative energy source with zero carbon emissions. The proton exchange membrane (PEM) fuel cell converts hydrogen fuel into electricity. As the name implies, the most important component of the fuel cell is the membrane itself. The PEM conducts protons through randomly distributed aqueous channels that are 5-10 nm in diameter. The morphology of the channel network is linked to the conductivity. Nafion, which is the current state-of-the-art PEM, is composed of a perfluorinated (PF) Teflon-like backbone and a sulfonic acid side-chain. However, PEM fuel cells require expensive platinum catalysts to facilitate the electrochemical reaction, which has impeded commercialization. Anion exchange membranes (AEM)s, which conduct hydroxide, present the possibility for implementing inexpensive Earth metal catalysts, which would significantly reduce the cost of production. Currently, the AEM performance is limited by poor conductivity. Understanding the nano-scale morphology of the channels could provide insight toward its conductive properties and overall performance. In this work, we investigated the surface morphology of an AEM analog to Nafion (PF AEM) using atomic force microscopy (AFM) and tapping-mode phase images. Given the chemical structure similarities between Nafion and the PF AEM, we hypothesize that the surface morphologies are similar, which could give rise to high conductivity. The morphology of the membrane was compared at dry, humidified, and ambient conditions using a closed imaging cell in both its chloride (PF AEM-Cl-) and hydroxide (PF AEM-OH-) form. Preliminary data of the PF AEM-Cl- shows hydrophilic domain diameter of ~16 nm, which is larger compared to Nafion (~8 nm) at ambient conditions. We plan to implement conductive-probe AFM, which maps the channels that are connected completely through the membrane. This study provides insight toward the future design of higher conducting AEMs.