Zhang Chao, Hutter Jürg, Sprik Michiel
Department of Chemistry-Ångström Laboratory , Uppsala University , Lägerhyddsvägen 1 , BOX 538, 75121 Uppsala , Sweden.
Institut für Chemie , Universität Zürich , Winterthurerstrasse 190 , CH-8057 Zürich , Switzerland.
J Phys Chem Lett. 2019 Jul 18;10(14):3871-3876. doi: 10.1021/acs.jpclett.9b01355. Epub 2019 Jun 28.
Surfaces of metal oxides at working conditions are usually electrified because of the acid-base chemistry. The charged interface compensated with counterions forms the so-called electric double layer. The coupling of surface chemistry and the electric double layer is considered to be crucial but is poorly understood because of the lack of information at the atomistic scale. Here, we used the latest development in density functional theory-based finite-field molecular dynamics simulation to investigate the pH dependence of the Helmholtz capacitance at electrified rutile TiO(110)-NaCl electrolyte interfaces. It is found that, because of competing forces from surface adsorption and from the electric double layer, water molecules have a stronger structural fluctuation at high pH, and this leads to a much larger capacitance. It is also seen that interfacial proton transfers at low pH increase significantly the capacitance value. These findings elucidate the microscopic origin of the same trend observed in titration experiments.
在工作条件下，金属氧化物表面通常因酸碱化学作用而带电。由抗衡离子补偿的带电界面形成了所谓的双电层。表面化学与双电层的耦合被认为至关重要，但由于缺乏原子尺度的信息，人们对此了解甚少。在此，我们利用基于密度泛函理论的有限场分子动力学模拟的最新进展，研究了带电金红石型TiO(110)-NaCl电解质界面处亥姆霍兹电容对pH的依赖性。研究发现，由于表面吸附和双电层的竞争作用，水分子在高pH值下具有更强的结构波动，这导致了更大的电容。还可以看到，低pH值下的界面质子转移显著增加了电容值。这些发现阐明了滴定实验中观察到的相同趋势的微观起源。
