Decoding the influence of monomer structures on the electrical double layer of alkaline fuel cells

Abstract

Alkaline polymer electrolytes (APEs) are extensively used in fuel cells and electrolysers due to their safety and low-cost advantages. Recently, scientists have explored their potential as electrochemical reaction catalysts, allowing APEs to function as ion transport channels and actively participate in catalytic reactions, exhibiting bifunctional characteristics. However, the key challenge in designing such materials lies in ensuring that the catalytic groups embedded within the polymer backbone can interact effectively with the electrode surface or reaction sites. Failure to do so would render them unable to participate in the electrocatalytic reactions occurring at the interface. This necessitates a deep understanding of the electric double-layer (EDL) structure at the electrode/APE interface. Despite numerous studies on improving their stability, a general understanding of the interfacial EDL structure is still lacking. To address this gap, we adopted state-of-the-art simulation approaches, combining constant potential and finite field methods, to investigate the EDL structures of two APEs (QAPS and QAPPT) at different electrode potentials. Our research findings indicate that, although these two APEs contain the same cationic groups, they exhibit distinctly different EDL structures on negatively charged surfaces. Specifically, when the electrode was negatively charged, the phenylene unit on the backbone of QAPPT was perpendicular to the surface, while the backbone of QAPS was displaced away from the surface. This study underscores the importance of interfacial double layers in influencing the performance of polymer electrolytes, aiding in understanding the polarisation behaviour on charged surfaces of polymer electrolytes and guiding how to modulate functional groups on these APEs to achieve catalytic effects. Furthermore, this work provides an effective method for studying the EDL structure of electrode/APE interfaces, which can be widely applied to research on various complex interfaces.