Electrocatalysis at the electrode-electrolyte interface: a combined DFT and classical force-field approach

电化学为利用可再生或可持续能源（如太阳能、风能或水力发电）制造燃料和化学品提供了一条途径。通过在电化学技术中加入催化剂，可以进一步提高这种电化学过程的效率、速率和产物选择性。虽然有效，但电催化的制造工艺非常复杂，很难预测催化材料和最佳性能所需的操作条件的最佳组合。该项目将发展理论和数学方法来理解液体溶剂中电催化反应的能量学，从而促进寻找改进的催化剂和制造工艺。该项目还包括培训不同教育水平的学生，并向代表性不足的群体伸出援手。在电极/电解质界面上模拟电催化过程的计算方法对于指导合理设计是必不可少的。在表面结合的反应物和生成物状态的理论描述方面，特别是密度泛函理论（DFT）的应用取得了很大进展。最近，在描述电催化过渡态方面的进展使估计反应障碍成为可能。然而，在这些进展中，对周围电解质的描述相对原始，尽管溶剂化效应对反应速率明显重要。该项目结合了最先进的DFT方法来计算过渡态，与经典的分子动力学（MD）模拟方法来计算溶剂化自由能。使能的概念是将在金属/真空界面处描述的DFT过渡态作为一个分子，插入到双层的电解质中。通过计算缓慢“开启”与周围流体相互作用所需的热力学功，已经开发了用于溶液中分子溶剂化自由能的MD模拟方法。这些方法将应用于过渡态本身，以及表面结合的反应物和产物。相对极性的反应物、过渡态和生成物与溶剂和电解质离子的相互作用更强，其自由能相应降低，对反应势垒也有相应的影响。这些重要的溶剂化效应对屏障和反应速率的影响关键取决于对表面附近水分子和离子的局部排列进行适当的平均。原子MD模拟是唯一适合于描述和平均这些局部安排。用新方法研究的第一个反应将包括电催化氢氧化和丙醇还原，与燃料电池和生物质电还原相关的技术反应。该方法将根据现有的实验数据进行验证，包括溶液相丙醇脱水障碍、界面水结构、双层电容、单晶Pt电极上的氢氧化障碍和丙醇电还原障碍。研究生和本科生都将开发和应用所提出的方法，并接受电化学、电子结构和分子建模方面的广泛教育。两位研究者将继续他们在研究中指导本科生的良好记录，在过去的5年里，他们共指导了48名本科生，共同撰写了22篇同行评议的出版物。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Electrochemistry offers a route to manufacturing fuels and chemicals from renewable or sustainable energy sources such as solar, wind, or hydroelectric power. The efficiency, rates, and product selectivity of such electrochemical processes can be further improved by incorporating catalysts into the electrochemical technology. Although effective, electrocatalytic manufacturing processes are highly complex, making it difficult to predict the best combinations of catalytic materials and operating conditions needed for optimal performance. The project will develop theoretical and mathematical methods to understand the energetics of electrocatalytic reactions in liquid solvents, thereby facilitating the search for improved catalysts and manufacturing processes. The project also involves training of students at various educational levels and outreach to underrepresented groups. Computational methods to model electrocatalytic processes at the electrode/electrolyte interface are essential to guide rational design. Much progress has been made in theoretical descriptions of surface-bound reactant and product states, particularly using density functional theory (DFT). More recently, advances in describing electrocatalytic transition states have enabled estimates of reaction barriers. However, in these advances the description of the surrounding electrolyte is comparatively primitive, despite the evident importance of solvation effects on reaction rates. The project combines state-of-the-art DFT methods to compute the transition state, with classical molecular dynamics (MD) simulation methods to compute solvation free energies. The enabling concept is to treat the DFT transition state described at the metal/vacuum interface as a molecule, to be inserted into the electrolyte in the double layer. MD simulation methods have been developed for solvation free energies of molecules in solution, by computing the thermodynamic work required to slowly "turn on" the interactions with surrounding fluid. These methods will be applied to the transition state itself, as well as to the surface-bound reactants and products. Relatively polar reactants, transition states, and products should more strongly interact with solvent and electrolyte ions, and their free energies lowered accordingly, with corresponding effects on reaction barriers. These important solvation effects on barriers and reaction rates depend crucially on proper averaging over local arrangements of water molecules and ions near the surface. Atomistic MD simulations are uniquely suited to describe and average over these local arrangements. The first reactions to be studied with the new methods will include electrocatalytic hydrogen oxidation and propanol reduction, reactions of technical relevance for fuel cells and biomass electroreduction. The developed approach will be validated against available experimental data, including solution phase propanol dehydration barriers, interfacial water structure, double-layer capacitance, hydrogen oxidation barriers on single-crystal Pt electrodes, and propanol electroreduction barriers. Both graduate and undergraduate students will develop and apply the proposed methods, and receive broad education in electrochemistry, electronic structure, and molecular modeling. Both investigators will continue their strong record of mentoring undergraduates in research, which together has resulted in 48 advised undergraduates who have co-authored 22 peer reviewed publications over the past 5 years.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.