离子-电子转移耦合动力学理论
Theory of coupled ion-electron transfer kinetics
摘要：
化学反应的微观理论基于过渡态理论，其中原子或离子经典地在能量势垒上转移，因为电子保持其基态。电子转移是根本不同的，并发生隧道响应溶剂波动。在这里，我们发展了耦合离子-电子转移理论，其中离子和溶剂分子协同波动以促进电子转移。我们推导出反应速率的一般公式，它取决于超电势，溶剂性质，电子供体/受体的电子结构，和过量的化学势的离子在过渡态。对于法拉第反应，该理论预测了具有浓度依赖性反应限制电流的曲线塔菲尔图。对于中等过电位，我们的公式减少到巴特勒-沃尔默方程，并解释其相关性，不仅在众所周知的限制大电子转移（溶剂重组）的能量，但也在相反的限制大离子转移能量。速率公式适用于锂离子电池，其中电极主体材料的还原与离子插入耦合。在磷酸铁锂的情况下，该理论准确地预测了交换电流的浓度依赖性的{ \it在operando} X射线显微镜测量没有任何可调参数。这些结果为界面工程铺平了道路，以提高离子嵌入率，不仅为电池，而且为离子分离和神经形态计算。
英文摘要：
The microscopic theory of chemical reactions is based on transition state theory, where atoms or ions transfer classically over an energy barrier, as electrons maintain their ground state. Electron transfer is fundamentally different and occurs by tunneling in response to solvent fluctuations. Here, we develop the theory of coupled ion-electron transfer, in which ions and solvent molecules fluctuate cooperatively to facilitate electron transfer. We derive a general formula of the reaction rate that depends on the overpotential, solvent properties, the electronic structure of the electron donor/acceptor, and the excess chemical potential of ions in the transition state. For Faradaic reactions, the theory predicts curved Tafel plots with a concentration-dependent reaction-limited current. For moderate overpotentials, our formula reduces to the Butler-Volmer equation and explains its relevance, not only in the well-known limit of large electron-transfer (solvent reorganization) energy, but also in the opposite limit of large ion-transfer energy. The rate formula is applied to Li-ion batteries, where reduction of the electrode host material couples with ion insertion. In the case of lithium iron phosphate, the theory accurately predicts the concentration dependence of the exchange current measured by {\it in operando} X-Ray microscopy without any adjustable parameters. These results pave the way for interfacial engineering to enhance ion intercalation rates, not only for batteries, but also for ionic separations and neuromorphic computing.
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