Zelovich Tamar, Tuckerman Mark E
Department of Chemistry, New York University (NYU), New York 10003, NY, USA.
Courant Institute of Mathematical Sciences, New York University (NYU), New York, NY 10012, USA.
Membranes (Basel). 2021 May 12;11(5):355. doi: 10.3390/membranes11050355.
Fuel cell-based anion-exchange membranes (AEMs) and proton exchange membranes (PEMs) are considered to have great potential as cost-effective, clean energy conversion devices. However, a fundamental atomistic understanding of the hydroxide and hydronium diffusion mechanisms in the AEM and PEM environment is an ongoing challenge. In this work, we aim to identify the fundamental atomistic steps governing hydroxide and hydronium transport phenomena. The motivation of this work lies in the fact that elucidating the key design differences between the hydroxide and hydronium diffusion mechanisms will play an important role in the discovery and determination of key design principles for the synthesis of new membrane materials with high ion conductivity for use in emerging fuel cell technologies. To this end, molecular dynamics simulations are presented to explore hydroxide and hydronium ion solvation complexes and diffusion mechanisms in the model AEM and PEM systems at low hydration in confined environments. We find that hydroxide diffusion in AEMs is mostly vehicular, while hydronium diffusion in model PEMs is structural. Furthermore, we find that the region between each pair of cations in AEMs creates a bottleneck for hydroxide diffusion, leading to a suppression of diffusivity, while the anions in PEMs become active participants in the hydronium diffusion, suggesting that the presence of the anions in model PEMs could potentially promote hydronium diffusion.
基于燃料电池的阴离子交换膜（AEMs）和质子交换膜（PEMs）被认为作为具有成本效益的清洁能源转换装置具有巨大潜力。然而，从原子层面深入理解AEM和PEM环境中氢氧根离子和水合氢离子的扩散机制仍是一项持续的挑战。在这项工作中，我们旨在确定控制氢氧根离子和水合氢离子传输现象的基本原子步骤。这项工作的动机在于，阐明氢氧根离子和水合氢离子扩散机制之间的关键设计差异，将在发现和确定用于新兴燃料电池技术的具有高离子电导率的新型膜材料合成的关键设计原则方面发挥重要作用。为此，我们进行了分子动力学模拟，以探索在受限环境中低水合状态下模型AEM和PEM系统中的氢氧根离子和水合氢离子溶剂化络合物及扩散机制。我们发现，AEMs中氢氧根离子的扩散主要是通过载体进行的，而模型PEMs中水合氢离子的扩散是结构性的。此外，我们发现AEMs中每对阳离子之间的区域为氢氧根离子扩散形成了瓶颈，导致扩散率受到抑制，而PEMs中的阴离子成为水合氢离子扩散的积极参与者，这表明模型PEMs中阴离子的存在可能会促进水合氢离子的扩散。
