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

Abstract

A surficial molecular dipole effect depending on ion‐molecular interactions has been crucial issues regarding to an interfacial potential, which can modulate solid electronic and electrochemical systems. Their properties near the interfacial region can be dictated by specific interactions between surface and adsorbates, but understandings of the corresponding details remain at interesting issues. Here, intuitive observations of an ionic pair formation‐induced interfacial potential shifts are presented with an ionovoltaic system, and corresponding output signal variations are analyzed in terms of the surficial dipole changes on self‐assembled monolayer. With aiding of photoelectron spectroscopies and density function theory simulation, the ionic pair formation‐induced potential shifts are revealed to strongly rely on a paired molecular structure and a binding affinity of the paired ionic moieties. Chemical contributions to the binding event are interrogated in terms of polarizability in each ionic group and consistent with chaotropic/kosmotropic character of the ionic groups. Based on these findings, the ionovoltaic output changes are theoretically correlated with an adsorption isotherm reflecting the molecular dipole effect, thereby demonstrating as an efficient interfacial molecular probing method under electrolyte interfacing conditions.

Ionovoltaics in energy harvesting and applications: A journey from early development to current state‐of‐the‐art

“…Subsequently, the dipole moment effect of molecular layers formed by ion pairing at the solid-liquid interface was investigated, using an electrolyte-SAM-electrode structured ionovoltaic device operating in push/release mode (Figure 6D). 53 The variation of the interfacial potential difference generated by the dipole moment of the molecular layer, which depends on the combination 54 of ion and molecular species was revealed by the ionovoltaic signals (Figure 6E). In particular, the ion specificity, which indicates that the stable pairing of ion and molecule strongly depends on their binding affinity, was interpreted by the Langmuir-Freundlich isotherm effect and DFT calculations.…”

“…49,50 Based on this, a theoretical analysis of the interfacial specificity in ionovoltaic phenomena was performed by interpreting the interfacial dipole in EDL and the charge effect. [51][52][53] In addition, a sophisticated water-immersed Hall measurement setup was designed to quantitatively analyze the electron density change in semiconductor due to ionic behavior at the solid-liquid interface from the perspective of solid-state physics based on semiconductor device theory. 54 Based on the fundamental theory of the ionovoltaics, the potential for developing novel biological/chemical sensing platforms and improving the performance of lithium-ion batteries and neuromorphic devices was confirmed.…”

“…Thus, the effect of changes in the electrical properties of the deposited indium tin oxide (ITO) film according to the sputtering conditions (Figure 7A) on the generated voltage and current of ionovoltaic device was investigated (Figure 7B). 64 There were two main methods for inducing oxygen vacancies in ITO films: increasing the partial pressure of the oxygen gas during deposition (Figure 7C) and controlling the working pressure of the 53 sputtering chamber to adjust the deposition rate (Figure 7D). [95][96][97] By manipulating these sputter-deposition conditions, variations in the electrical and structural properties of the ITO film can be achieved, leading to changes in the ionovoltaic output signal.…”

“…Ionovoltaic devices have the advantage of controlling the solid-liquid interfacial properties through thin-film processing and chemical surface treatment techniques. 53,89 This suggests that it is necessary to analyze the relationship between the interfacial properties and the output signal of the device due to the solute-surface interaction at the solid-liquid interface. 72,84 In addition, the fundamental principles of ionovoltaics and the material and 63 interfacial engineering approaches show the possibility of utilizing it as an analytical tool for various solid-liquid interfacial phenomena and as a biological/chemical sensing platform for the detection of substances in the liquid phase.…”

Why does water in porous carbon generate electricity? Electrokinetic role of protons in a water droplet-induced hydrovoltaic system of hydrophilic porous carbon

“…Therefore, H 3 O + and OH − are the only mobile charge carriers considered in this model. Other ions and their interactions with the substrates can become crucial 44,45 especially for harvesters utilizing natural water sources ( e.g. , Na + ions on surface can have equivalent effect of p-doped carbon and plausibly impose electron gradient 8 ), but the present study only focused on the case of diluted water.…”