Origin of Solvent Dependency of the Potential of Zero Charge

Weiqiang Tang; Shuangliang Zhao; Jun Huang

doi:10.1021/jacsau.3c00552

Origin of Solvent Dependency of the Potential of Zero Charge

JACS Au. 2023 Nov 15;3(12):3381-3390. doi: 10.1021/jacsau.3c00552. eCollection 2023 Dec 25.

Authors

Weiqiang Tang^{1

2}, Shuangliang Zhao^{1

3}, Jun Huang^{2

4}

Affiliations

¹ State Key Laboratory of Chemical Engineering and School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China.
² Institute of Energy and Climate Research, IEK-13: Theory and Computation of Energy Materials, Forschungszentrum Jülich GmbH, Jülich 52425, Germany.
³ Guangxi Key Laboratory of Petrochemical Resource Processing and Process Intensification Technology and School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China.
⁴ Theory of Electrocatalytic Interfaces, Faculty of Georesources and Materials Engineering, RWTH Aachen University, Aachen 52062, Germany.

Abstract

Fundamental properties of the Au(111)-KPF₆ interface, particularly the potential of zero charge (PZC), exhibit pronounced variations among solvents, yet the origin remains largely elusive. In this study, we aim to link the solvent dependency to the microscopic phenomenon of electron spillover occurring at the metal-solution interface in heterogeneous dielectric media. Addressing the challenge of describing the solvent-modulated electron spillover under constant potential conditions, we adopt a semiclassical functional approach and parametrize it with first-principles calculations and experimental data. We unveil that the key variable governing this phenomenon is the local permittivity within the region approximately 2.5 Å above the metal edge. A higher local permittivity facilitates the electron spillover that tends to increase the PZC on the one hand and enhances the screening of the electronic charge that tends to decrease the PZC on the other. These dual effect lead to a nonmonotonic relationship between the PZC and the local permittivity. Moreover, our findings reveal that the electron spillover induces a capacitance peak at electrode potentials that are more negative than the PZC in concentrated solutions. This observation contrasts classical models predicting the peak to occur precisely at the PZC. To elucidate the contribution of electron spillover to the total capacitance, we decompose the total capacitance into a quantum capacitance of the metal C_q, a classical capacitance of electrolyte solution C_c, and a capacitance C_qc accounting for electron-ion correlations. Our calculations reveal that C_qc is negative due to the promoted electron spillover at more negative potentials. Our work not only reveals the importance of local permittivity in tuning the electron spillover but also presents a viable theoretical approach to study solvent effects on electrochemical interfaces under operating conditions.