Determination of the step dipole moment and the step line tension on Ag(001) electrodes

Understanding the Effects of Electrode Material, Single Crystal Facet, and Electrolyte Ion on the Helmholtz Capacitance of Metal/Aqueous Solution Interfaces

The comprehensive interpretation of the measured differential Helmholtz capacitance curve is vital for advancing our understanding of the interfacial structure. While several possible physical effects contributing to the Helmholtz capacitance have been proposed theoretically, combining those factors to explain the experimentally observed potential-dependent capacitance profile remains a significant challenge. In this study, we employ ab initio molecular dynamics simulations to model various metal/solution interfaces. Our investigation primarily emphasizes the substantial effect of water chemisorption on the potential-dependent behavior of the Helmholtz capacitance. Additionally, we identify other critical factors that profoundly impact the Helmholtz capacitance: (1) Ions with low hydration energy hinder the availability of surface sites for water adsorption, resulting in a diminished enhancement of capacitance from water chemisorption. (2) Using large-sized ions leads to an expansion of the Helmholtz layer, causing a decrease in the Helmholtz capacitance. (3) Metal surfaces with higher affinity for water attract water adsorption at lower potentials, resulting in a lower peak potential for the differential Helmholtz capacitance curve.

Modeling stepped Pt/water interfaces at potential of zero charge with ab initio molecular dynamics

It is worthwhile to understand the potentials of zero charge (PZCs) and structures of stepped metal/water interfaces, because for many electrocatalytic reactions stepped surfaces are more active than atomically flat surfaces. Herein, a series of stepped Pt/water interfaces are modeled at different step densities with ab initio molecular dynamics (AIMD). It is found that the structures of Pt/water interfaces are significantly influenced by the step density, particularly for the distribution of chemisorbed water. The step sites of metal surfaces are more preferred for water chemisorption than the terrace sites, and until the step density is very low, water will chemisorb on the terrace. In addition, it is revealed that the PZCs of stepped Pt/water interfaces are generally smaller than that of Pt(111), and the difference is mainly attributed to the difference in the work function, providing a simple way to estimate the PZCs of stepped metal surfaces. Finally, it is interesting to see that the Volta potential difference is almost same for Pt/water interfaces with different step densities, although their interface structures and magnitude of charge transfer clearly differ.

Kink energy and kink dipole moments on vicinal Au(001) in halide electrolytes

Using electrochemical scanning tunnelling microscopy, we measured the potential-dependent kink energy and the corresponding dipole moments of kinks at step edges on vicinal Au(001) surfaces in chloride and bromide containing electrolytes. Combining the results of the potential dependence of the kink energy with impedance spectroscopy data for the surface charge, we can directly deduce the dipole moment of kinks at the Au steps with co-adsorbed Cl(-) and Br(-), respectively. We find μ(Cl) = (6.0 ± 0.7) × 10(-3) eÅ and μ(Br) = (10.1 ± 0.6) × 10(-3) eÅ.

Potential steps at C₆₀-TiOPc-Ag(111) interfaces: ultrahigh-vacuum-noncontact scanning probe metrology

Nanoscale structure-electric potential relations in films of the organic molecular semiconductors C(60) and titanyl phthalocyanine (TiOPc) on Ag(111) have been measured under UHV conditions. Noncontact force methods were utilized to image domain structures and boundaries with molecular resolution, while simultaneously quantifying the local surface electric potential. Sensitivity and spatial resolution for the local potential measurement were first established on Ag(111) through direct observation of the electrical dipole and potential step, φ(step) = 10 ± 3 mV, of monatomic crystallographic steps. A local surface potential increase of 27 ± 11 mV occurs upon crossing the boundary between the neat Ag(111) surface and C(60) islands. Potential steps in binary C(60)-TiOPc films, nanophase-separated into crystalline C(60) and TiOPc domains, were then mapped quantitatively. The 207 ± 66 mV potential step across the C(60)-to-TiOPc domain boundary exhibits a 3.6 nm width that reflects the spatial resolution for electric potential across a material interface. The absence of potential asymmetry across this lateral interface sets the upper bound for the C(60)-TiOPc interface dipole moment as 0.012 e nm.