Lingyu Yang

Chemical and Biomolecular Engineering

Faculty Advisor: Jennifer Schaefer

Development of a Novel Polymer Membrane Platform for Alkaline Fuel Cell Electrolyte Application

With the continually increasing demand for clean and renewable energy worldwide, tremendous efforts have been made to seek new energy alternatives. Electrochemical storage and conversion devices have been recognized as some of the most critical technologies in overcoming fossil fuel exhaustion and global pollution. Among these clean technologies, fuel cells outperform others because of high power generation efficiency, high specific energy, and low environmental pollution. Fuel cells represent environmentally friendly energy devices, including proton exchange membrane fuel cells (PEMFCs), and anion exchange membrane fuel cells (AEMFCs), et al. Ranging in potential application from grid-scale storage to the electrification of transportation, this research seeks to contribute to the pursuit of a future without a reliance on fossil fuels.

AEMFCs have many advantages over PEMFCs such as the wider selection of electrocatalysts, less metal corrosion, and lower cost. However, the anion exchange membranes (AEMs) reported previously were not as conductive and stable as the proton exchange membranes (PEMs), resulting in reduced performance in real applications. To address the issues of AEMs, the concept of novel AEMs was proposed which utilized a recently developed method, Friedel-Crafts hydroxylation. This project is in collaboration with Prof. Haifeng Gao’s group (Dept. of Chemistry and Biochemistry) and two different platforms (DFr and BrBB polymers)were designed. Only one other research group worldwide is pursuing this material platform. The group believes that this material platform has a high potential for success due to specific reasons (low-cost polymerization method, stability of backbone, et al) intrinsic to the platform. This work is concerned with using the above polymers as solid-state electrolyte to facilitate the movement of hydroxide, focusing specifically on how the polymer composition and structure impact species transport and electrochemical performances. Relevant measurements which have been conducted are the first use of fuel cell membranes in our research group and have established these measurement protocols. 

Project Objectives

This work thus far has resulted in a systematical comparison between three model compounds whose structures mimic the prepared polymers, which identified polymer design requirements for effective long dangling modulation of quaternary ammoniums, leading to enhanced stability in alkaline media. Some potential good-performing structures have been screened. These encouraging preliminary data indicate this project has a high likelihood of yielding interesting and practical results.

To continue the research, the first objective is to characterize the relationships between polymer chain sequence (including both random copolymer and block copolymer), membrane mesoscale structure, ionic conductivity, and mechanical properties. It is the first time that the structure containing crosslinker is introduced into AEMs. Therefore, the structure-property relationship between varied crosslink density and QAs ratios will be first elucidated. In addition, here it is proposed that in BrBB polymer, crosslink density or hydrophobic ratio would dominate and change material morphology, which influences the mechanical performance of AEMs, and hence work is also attempted on fabricating BrBB polymer membrane with great mechanical robust structure, as well as outstanding alkaline stability via changing the above two parameters.