Committee Members:

Dr. Paul Kohl, Advisor, ChBE

Dr. Seung Soon Jang, Co-Advisor, MSE

Dr. Donggang Yao, MSE

" In Situ Functionalization Of Anion-Conducting Solid Polymer Electrolyte Membranes”

ABSTRACT

Hydrogen is a viable option for storage and on-spot generation of energy. Alkaline electrolyzers and fuel cells have several advantages over acidic counterparts such as simple fabrication, non-precious metal catalysts and low crossover. It has been shown that crosslinked anion–exchange membranes synthesized by vinyl addition polymerization of norbornene show excellent performance in alkaline electrochemical devices. However, a long reaction time is needed for converting the tethered bromoalkyl moiety in the polymer to a quaternary ammonium head-group because a tertiary amine has to diffuse into the polymer. This amination process is not compatible with the roll-to-roll membrane formation process. In this study, anion exchange membranes have been prepared by in situ amination of the functionalized polymer during membrane casting. The scope of three different tertiary amine: Trimethyl amine, Triethyl amine and N-methyl piperidine was investigated for the in situ membrane casting process. The polymers used in this study were also in situ crosslinked with N,N,N’ ,N’ - tetramethyl-1,6-hexanediamine during membrane casting to prevent excessive water uptake. By changing the reaction solvent, temperature, and concentration, it was possible to balance the reaction kinetics while still maintaining polymer solubility to cast membranes. The conversion was monitored as a function of reaction time (using NMR) and the reaction conditions were optimized to develop a novel process of producing pre-functionalized membranes that is compatible with the current roll-to-roll infrastructure. Membranes having high ion exchange capacity (upto 3.4 meq g-1 ) and high ionic conductivity (upto 56 mS cm-1 at room temperature) were prepared using this process. Precisely controlling the reaction time made it possible to directly cast quaternized membranes on a roll-to-roll timescale, thus avoiding the need for the long-duration, ex situ amination step. Alkaline electrolyzer performance with these in situ aminated membranes showed comparable performance to membranes prepared by the conventional, ex situ amination method.