Exploring how cation entropy influences electric double layer formation and electrochemical reactivity
Exploring how cation entropy influences electric double layer formation and electrochemical reactivity
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DOI：
10.1039/d3sm01302b
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发表时间：
2023-12-01
期刊：
影响因子：
3.4
通讯作者：
Gebbie，Matthew A.
中科院分区：
文献类型：
--
作者：
Liu，Beichen;Guo，Wenxiao;Gebbie，Matthew A.
双电层对储能和电催化装置的性能至关重要。虽然双层的形成源于静电相互作用，但电双层的性质是由静电和熵驱动力的平衡决定的。有利的离子-表面静电相互作用吸引反离子到带电表面来补偿或“屏蔽”电位，但是这些相同的离子从体库到界面的限制会导致熵罚。在这里，我们使用双价咪唑离子液体及其单价类似物，以CO2电还原为模型反应，探索阳离子价和熵如何影响双层形成和电化学反应性。我们发现二价和一价阳离子表现出相似的CO2还原动力学，但由于快速电化学诱导的绝缘双离子（bi）碳酸盐膜的沉淀，其稳态反应性差异很大。利用原位表面增强拉曼散射光谱，我们发现两种离子液体在相似的电位下发生电位依赖的阳离子重定向，但在二价阳离子中引入共价键赋予更有序的双层结构，有利于（bi）碳酸盐的沉淀。在混合的一价-二价电解质中，我们发现即使在非常低的相对浓度下，二价阳离子也会优先积聚在表面，从而主导界面性质。我们的发现证实了离子熵在调节局部电化学环境中起着关键作用。此外，我们强调了双层性质如何对在界面上积累的最低熵惩罚的反离子的性质敏感。总的来说，我们说明了离子熵提供了一个新的调节反应微环境的方法，并揭示了熵如何在调节混合离子电解质的电化学反应性中起主要作用。
Electric double layers are crucial to energy storage and electrocatalytic device performance. While double layer formation originates in electrostatic interactions, electric double layer properties are governed by a balance of both electrostatic and entropic driving forces. Favorable ion–surface electrostatic interactions attract counterions to charged surfaces to compensate, or “screen,” potentials, but the confinement of these same ions from a bulk reservoir to the interface incurs an entropic penalty. Here, we use a dicationic imidazolium ionic liquid and its monovalent analogue to explore how cation valence and entropy influence double layer formation and electrochemical reactivity using CO2 electroreduction as a model reaction. We find that divalent and monovalent cations display similar CO2 reduction kinetics but differ vastly in steady-state reactivity due to rapid electrochemically induced precipitation of insulating dicationic (bi)carbonate films. Using in situ surface-enhanced Raman scattering spectroscopy, we find that potential-dependent cation reorientation occurs at similar potentials between the two ionic liquids, but the introduction of a covalent link in the divalent cation imparts a more ordered double layer structure that favors (bi)carbonate precipitation. In mixed monovalent-divalent electrolytes, we find that the divalent cations dominate interfacial properties by preferentially accumulating at surfaces even at very low relative concentrations. Our findings confirm that ion entropy plays a key role in modulating local electrochemical environments. Furthermore, we highlight how double layer properties are sensitive to the properties of counterions that pay the lowest entropic penalty to accumulate at interfaces. Overall, we illustrate that ion entropy provides a new knob to tune reaction microenvironments and unveil how entropy plays a major role in modulating electrochemical reactivity in mixed ion electrolytes.