Department of Physics and School of Molecular Sciences, Arizona State University, P.O. Box 871504, Tempe, Arizona 85287-1504, USA.
J Chem Phys. 2018 Apr 21;148(15):154501. doi: 10.1063/1.5022709.
A theory of redox reactions involving electron transfer between a metal electrode and a polarizable molecule in solution is formulated. Both the existence of molecular polarizability and its ability to change due to electron transfer distinguish this problem from classical theories of interfacial electrochemistry. When the polarizability is different between the oxidized and reduced states, the statistics of thermal fluctuations driving the reactant over the activation barrier becomes non-Gaussian. The problem of electron transfer is formulated as crossing of two non-parabolic free energy surfaces. An analytical solution for these free energy surfaces is provided and the activation barrier of electrode electron transfer is given in terms of two reorganization energies corresponding to the oxidized and reduced states of the molecule in solution. The new non-Gaussian theory is, therefore, based on two theory parameters in contrast to one-parameter Marcus formulation for electrode reactions. The theory, which is consistent with the Nernst equation, predicts asymmetry between the cathodic and anodic branches of the electrode current. They show different slopes at small electrode overpotentials and become curved at larger overpotentials. However, the curvature of the Tafel plot is reduced compared to the Marcus-Hush model and approaches the empirical Butler-Volmer form with different transfer coefficients for the anodic and cathodic currents.
提出了一种涉及金属电极和溶液中可极化分子之间电子转移的氧化还原反应理论。分子极化率的存在及其由于电子转移而改变的能力将这个问题与经典界面电化学理论区分开来。当氧化态和还原态的极化率不同时，驱动反应物越过活化能垒的热涨落统计变得非高斯。将电子转移问题表述为两个非抛物自由能面的交叉。提供了这些自由能面的解析解，并以对应于溶液中分子的氧化态和还原态的两个重组能的形式给出了电极电子转移的活化能垒。因此，与电极反应的单参数马库斯公式相比，新的非高斯理论基于两个理论参数。该理论与能斯特方程一致，预测了电极电流的阴极和阳极分支之间的不对称性。它们在小电极过电势下具有不同的斜率，并在较大过电势下变得弯曲。然而，与马库斯-休尔模型相比，塔菲尔图的曲率减小，并接近经验的巴特勒-沃尔默形式，对于阳极和阴极电流具有不同的传递系数。
