Probing consequences of anion-dictated electrochemistry on the electrode/monolayer/electrolyte interfacial properties

Abstract

Altering electrochemical interfaces by using electrolyte effects or so-called “electrolyte engineering” provides a versatile means to modulate the electrochemical response. However, the long-standing challenge is going “beyond cyclic voltammetry” where electrolyte effects are interrogated from the standpoint of the interfacial properties of the electrode/electrolyte interface. Here, we employ ferrocene-terminated self-assembled monolayers as a molecular probe and investigate how the anion-dictated electrochemical responses are translated in terms of the electronic and structural properties of the electrode/monolayer/electrolyte interface. We utilise a photoelectron-based spectroelectrochemical approach that is capable of capturing “snapshots” into (1) anion dependencies of the ferrocene/ferrocenium (Fc/Fc + ) redox process including ion-pairing with counter anions (Fc + –anion) caused by differences in Fc + –anion interactions and steric constraints, and (2) interfacial energetics concerning the electrostatic potential across the electrode/monolayer/electrolyte interface. Our work can be extended to provide electrolyte-related structure-property relationships in redox-active polymers and functionalised electrodes for pseudocapacitive energy storage.

Probing an Interfacial Ionic Pairing‐Induced Molecular Dipole Effect in Ionovoltaic System

“…This favorable adsorption could be attributed to the hydrophobic nature of the surfactant molecules and a pairing-induced charged group stabilization. [4,25] The ionovoltaic generation can be influenced by several factors such as the droplet motion-dependent contact area variation, resistor-capacitor discharging, and an interfacial potential difference between the electrolyte (droplet) and the Si electrode (∑ψ). [17,20] Among those factors, the first two terms had negligible effects to the output voltages changes (experimental section, Figure S6b, Supporting Information).…”

“…This suggested that, with a rational design of interfacial molecular layer, the ionovoltaic system could be an analytic system for observing the ionic and intermolecular interactions, such as interfacial ad-/desorption and chemical reaction, at the interfacial region without intricate experimental conditions. In conjunction with conventional surficial and interfacial analytic techniques, such as optical measurements (e.g., IR and Raman scattering spectroscopy, sum frequency generation), [4,35,36] the ionovoltaic system might be an informative tool for analyzing solid/liquid interfacial phenomena in various liquid interfacing devices. [4,6,10]…”

“…In conjunction with conventional surficial and interfacial analytic techniques, such as optical measurements (e.g., IR and Raman scattering spectroscopy, sum frequency generation), [4,35,36] the ionovoltaic system might be an informative tool for analyzing solid/liquid interfacial phenomena in various liquid interfacing devices. [4,6,10]…”

“…Interfacial potential effects, originated from intrinsic molecular dipoles at a spontaneously assembled molecular layer (self-assembled monolayer (SAM)), has been interesting issues in diverse fields, such as electronic and electrochemical interfaces. [1][2][3][4] In their studies, influences of regulated molecular structures to interfacial potential effects, affecting on a vicinity of (semi-)conducting layer, were systemically discussed. [1,2,4] As an offshoot of them, ion-surface molecular interactions at SAM were revealed to altering dipolar moment of the surface molecules or modulating the intrinsic potential emanating from the SAM, thereby controlling electron energetics of the solid electrode or an electrostatic potential profiles at electrical double layer.…”

“…[1][2][3][4] In their studies, influences of regulated molecular structures to interfacial potential effects, affecting on a vicinity of (semi-)conducting layer, were systemically discussed. [1,2,4] As an offshoot of them, ion-surface molecular interactions at SAM were revealed to altering dipolar moment of the surface molecules or modulating the intrinsic potential emanating from the SAM, thereby controlling electron energetics of the solid electrode or an electrostatic potential profiles at electrical double layer. [5][6][7][8][9][10] These phenomena were based on various specific interactions, originated from physicochemical natures of associating species [11][12][13][14][15] (e.g., coordination bonding, coulombic pairing, and hydrogen bonding), and made the surface molecule redistribute its charges by building new bond dipoles or structural changes, thereby altering the dipolar characteristic of SAM.…”