Multi-scale modeling of electrochemical interfaces: New methods and applications to RuO2 surfaces

电化学界面的计算模拟是在分子水平上理解电化学过程的关键方法。由于静电相互作用、电荷转移过程和双电层的形成，固体/液体界面具有显著的复杂性。考虑到电化学界面复杂的结构和动态过程，以及现有的计算资源，用从头算的电子结构理论模拟现实模型是不可行的。在这个项目中，我们开发了新的模拟协议，该协议结合了多个尺度的模拟方法，以实现催化剂表面电化学反应的预测，但计算成本低廉。作为一个典型的例子，我们重点研究了RuO2/电解质界面上的电化学水氧化反应。RuO2是电解槽中析氧反应最有效的催化剂之一，但催化剂的形态和在操作条件下的稳定性仍存在争议。利用密度泛函和经典理论相结合的互补方法，研究了电化学过程固有的多尺度性质，包括在纳秒时间尺度上的快速电荷再分配和电解质扩散过程。基于从头算热力学表面自由能计算对表面结构的初步筛选，选择的结构用于量子/分子力学（QM/MM）和隐式溶剂化技术的发展。实验数据和从头算分子动力学模拟验证了所实现的方法，该方法严格按照密度泛函理论的同一水平处理系统的所有组成部分。通过对开路和工作条件下的RuO2/电解质界面的模拟，我们解决了与电位、pH和电双层有关的形貌、稳定性和活性的基本问题。

The computational simulation of electrochemical interfaces is a key methodology to understand electrochemical processes at a molecular level. Solid/liquid interfaces are subject to significant complexity due to the interplay of electrostatic interactions, charge transfer processes and the formation of an electrical double layer. Considering the intricate structure and dynamical processes at electrochemical interfaces and currently available computational resources, the simulation of realistic models with ab initio electronic structure theory is infeasible. In this project we develop new simulation protocols which combine simulation methods at multiple scales to achieve predictive, yet computationally inexpensive, models of electrochemical reactions at catalyst surfaces.As a prototypical example we focus on the electrochemical water oxidation reaction at RuO2/electrolyte interfaces. RuO2 is one of the most efficient catalysts for the oxygen evolution reaction in electrolyzers, but catalyst morphology and stability at operating conditions are still under debate. The intrinsic multiscale nature of electrochemical processes, which involve fast charge redistribution but also electrolyte diffusion processes at a nanosecond timescale, are addressed by complementary methods combining density functional and classical theories. Based on initial screening of surface structures using surface free energy calculations by ab initio thermodynamics, selected structures are used for the development of quantum/molecular mechanics (QM/MM) and implicit solvation techniques. The implemented methods are validated by experimental data and ab initio molecular dynamics simulations treating all components of a system strictly at the same level of density functional theory. From simulations of RuO2/electrolyte interfaces at open-circuit and operating conditions we address fundamental questions concerning morphology, stability and activity in relation to potential, pH and electrical double layer.