Separation‐Controlled Redox Reactions

Abstract

In the era of molecular devices and nanotechnology, precise control over electron-transfer processes is strongly desired. However, redox reactions are usually characterized by reaction equilibrium constants strongly departing from unity. This leads to strong favoring of either reactants or products and does not permit subtle control of transferred charge (doping).Here we propose, based on theoretical studies for periodic systems, how charge transfer between reactants could be finely manipulated in the epitaxially grown system composed of extremely strong oxidizer, reducing agent, and an inert separator-the key factor of control.Electron transfer reactions, together with acid-base ones, constitute the most important types of elemental processes in chemistry. One unique feature of redox reactions is that their equilibrium constants strongly depart from unity. For example, for a model one-electron reaction where the standard redox potentials, E 0 , for the two involved redox pairs differ by a mere 0.1 V, the reaction equilibrium constant, K [Eq. (1)] K eq ¼ expðDE 0 F=RTÞ ð1Þ

Charge doping to flat AgF2 monolayers in a chemical capacitor setup

“…In a simple capacitor model the charge transfer behaves as: with m 0 a constant. 13 Therefore, at larger separation, a change of m has a smaller effect on δ n Ag , as expected. Given the Ag/F vs. Cu/O analogy, 2,35 and the similarity of their UHBs, it is expected that the optimum electron doping level for the [AgF 2 ] sheet corresponds to ca.…”

“…Thus, nominally neutral MgO is capable of serving as a charge reservoir vs. AgF 2 due to the substantial difference of chemical potentials between them prior to charge transfer. 13…”

“…For the study of electron- and hole-doping scenarios in the chemical capacitor setup, we performed calculations with the same settings as in our previous studies of surfaces/heterostructures with AgF 2 monolayers. 3,13,28 Magnetic interactions in the AgF 2 monolayer were evaluated with the antiferromagnetic coupling constant J 2D (“2D” refers to two-dimensional coupling in the monolayer), which was calculated using collinear configurations and a broken symmetry method as J 2D = E AFM − E FM (where E AFM and E FM are the energies per silver of the antiferromagnetic and ferromagnetic solutions, respectively). By this convention, J 2D is negative in AFM systems.…”

“…We argue that the degree of electron transfer from an oxide substrate to AgF 2 electron sink can be finely controlled through spatial separation of AgF 2 and oxide by a variable number of fluoride layers; this is a so called “chemical capacitor” setup, which three of us (AG, JL, WG) have recently proposed. 13 As our DFT calculations show, manipulation of the thickness of the oxide layers and the thickness of the fluoride separator between them and the [AgF 2 ] surface sheet, permits fine adjustment of the doping level up all the way from the underdoped, via the optimum doped up to the overdoped regime, thus allowing for superconducting T C tuning. Finally, the third part of this work summarizes our findings related to the possibility of hole-doping to the flat AgF 2 monolayer.…”

“…The rationale of these two different choices is that for the determination of doping, the important quantities are the capacitance of the AgF 2 layer (or the electronic compressibility) and the difference in the chemical potential that the two layers would have if the interlayer Coulomb interaction is neglected. 13 Both quantities are very sensitive to the presence of the charge gap at half-filling. Furthermore, we know that above some critical doping long-range order would vanish and only a finite magnetic correlation length would remain.…”