Capacitance spectroscopy and density functional theory

Abstract

The redox capacitance and its associated quantum component arising from the charging of molecular levels from coupled metallic states are resolvable and quantified experimentally by capacitance spectroscopy (CS). Herein we relate both this N-electron system capacitance directly to conceptual chemistry density functional theory (DFT) and the charging magnitude and associated quantum capacitive term (which resemble those introduced by Serge Luryi) to the Kohn-Sham frontier molecular orbital associated energies for isolated molecules and DFT calculated redox density of states (DOS) at metal-molecule junctions for a single molecule and molecular films confined at metallic interfaces. DFT computational analyses reveal the orbital energetic alignment between the iron redox site and those states in the metal specifically when metal-molecule junctions are formed. The impact of this on the resolved chemical softness and capacitance is also revealed. These analyses, additionally, are shown to numerically resolve redox capacitance in a manner that accurately reproduces experimental observations for molecular films. These observations both theoretically underpin CS and provide guidance on its optimised application in interfacial analyses involving molecular electrochemistry and derived sensory applications.

The intrinsic volumetric capacitance of conducting polymers: pseudo-capacitors or double-layer supercapacitors?

“…It has been used to estimate the capacitance of few-electron semiconductor quantum dots electrostatically dened by split-gates in a twodimensional electron gas, 36,37 the capacitance of carbon nanotubes 38 and graphene nanoribbons, 39 and the capacitance of molecular clusters and layers. 40,41 In this paper, we use this approach for the case of conducting polymers, particularly focusing on PEDOT. For our calculations, we nd that the volumetric capacitance of PEDOT is on the order of 100 F cm À3 , which is within the range of reported experimental measurements.…”

“…This equation will be our starting point in the calculation of the volumetric capacitance of conducting polymers. For a quantum system, it is instrumental to represent a change of the chemical potential, eqn (1), as a sum of two terms, 39,40,45 Dm…”

“…Apparently, for a classical conductor, the DOS is innite and therefore DV Q ¼ 0. [39][40][41] Using eqn (7) and the denition of the capacitance, eqn (4), we can separate the total volumetric capacitance C(N) into classical and quantum contributions, [39][40][41]45 1…”

Electrochemical Impedance Spectroscopy Based Biosensors: Mechanistic Principles, Analytical Examples and Challenges towards Commercialization for Assays of Protein Cancer Biomarkers

“…Davis's group published a series of papers on impedance‐derived capacitance spectroscopy and its diagnostic utility (for detection of prostatic acid phosphatase down to 11 pM and C‐reactive protein down to 28 pM) ,…”

A dual marker label free electrochemical assay for Flavivirus dengue diagnosis

“…The impedance raw data can be converted to capacitance complex function, as shown in (c). The redox capacitance (C r ) can be estimated by semicircle diameter (Fernandes et al, 2014;Bueno et al, 2012Bueno et al, , 2015. Conditions: measurements performed at E in potential (≈ 400 mV x Ag|AgCl).…”