While polymer membranes are used to remove salts from environmental and industrial electrolytes, it remains a significant challenge to engineer them to isolate a single dissolved species from complex mixtures, which is important for lithium mining, battery and magnet recycling, and microelectronics. Underpinning this challenge has been a lack of understanding of rate-limiting mechanisms in selective ion transport. Here, we show that hydrated ions exhibit higher free energies of activation when crossing solution-membrane interfaces (i.e., partitioning) than when diffusing through polymers, which challenges historical assumptions embedded in widely used models of membrane performance. We further articulate a framework benchmarked with quantitative capabilities for predicting how functionality within polymer membranes or at their surfaces affects selectivity toward individual dissolved species.

虽然聚合物膜用于去除环境和工业电解质中的盐，但对其进行工程设计以从复杂的混合物中分离出单一溶解的物质仍然是一个重大挑战，这对于锂开采、电池和磁体回收以及微电子学非常重要。支撑这一挑战的原因是缺乏对选择性离子传输的限速机制的了解。在这里，我们表明，水合离子在穿过溶液-膜界面（即分配）时比在聚合物中扩散时表现出更高的活化自由能，这挑战了广泛使用的膜性能模型中嵌入的历史假设。我们进一步阐明了一个以定量能力为基准的框架，用于预测聚合物膜内或其表面的功能如何影响对单个溶解物种的选择性。