Anion Exchange Membranes Based on Quaternary Ammonium Cations and Modified Quaternary Ammonium Cations

Benefiting from the fast oxidation kinetics in alkali media, compact structure, zero emission, low fuel permeation, and the application of inexpensive non-precious metal catalysts, anion exchange membrane fuel cells (AEMFCs) have drawn growing attention in recent decades. The development of anion exchange membranes (AEMs), the essential component of AEMFCs, with high hydroxide ion conductivity, excellent mechanical stability as well as long-term durability is an important area of investigation in materials science research for fuel cell applications. A precise molecular design may result in membranes that facilitate ion conduction through well-defined ion conductive channels as well as excellent base stability against nucleophilic reactions. A number of viable cations have been tethered on to the polymer matrix as worthwhile candidates for AEMs in alkaline fuel cells. This chapter is an overview mainly focused on the various recent approaches made toward polymer membranes modified with quaternary ammonium (QA) cations aimed at high operating stability and improved electrochemical performance. Tethering various alkyl extender chains and fabricating multication side chains on to the polymer backbone using different quaternization strategies, application of cyclic QA structures, etc. are also discussed here, at length. We present a detailed examination of their synthetic methods, application in fuel cell in terms of the working principle, alkaline stability and degradation mechanism, fabrication of the MEA, as well as their performance optimization in fuel cells. This chapter also discusses the challenges and mitigation strategies associated with the present AEMs for fuel cell application.