Measurement of the combined quantum and electrochemical capacitance of a carbon nanotube

Jinfeng Li,Peter J Burke

doi:10.1038/s41467-019-11589-9

Abstract

The nature of the electronic interface between a nanotube and solvated ions in a liquid electrolyte is governed by two distinct physical phenomena: quantum and chemical. The quantum component arises from the sharply varying electronic density of states and the chemical component arises from ion screening and diffusion. Here, using an integrated on-chip shield technology, we measure the capacitance of one to a few nanotubes quantitatively as a function of both bias potential (from −0.7 V to 0.3 V) and ionic concentration (from 10 mM to 1 M KCl) at room temperature. We determine the relative contributions of the quantum and electrochemical capacitance, and confirm the measurements with theoretical models. This represents an important measurement of the quantum effects on capacitance in reduced dimensional systems in contact with liquid electrolytes, an important and emerging theme in the interface between nanotechnology, energy, and life.

Highlights

The nature of the electronic interface between a nanotube and solvated ions in a liquid electrolyte is governed by two distinct physical phenomena: quantum and chemical
The capacitance plays an important role in energy storage technologies such as batteries and supercapacitors[4,5,6], and governs the behavior of numerous electrochemical sensors[7]
What is the effect of this on the capacitance between a reduced dimensional system and a liquid electrolyte? While this has been addressed in theory, in practice for d < 2, it has been impossible to answer for one very important practical reason: It is almost immeasurably small

Summary

Introduction

The nature of the electronic interface between a nanotube and solvated ions in a liquid electrolyte is governed by two distinct physical phenomena: quantum and chemical. The “classic” Debye layer capacitance deviates from textbook behavior when the radius of curvature of the electrode becomes comparable to the solvated ion radius, of the order of 1 nm. This can occur in one of two topologies: Nanocaves, and nano-electrodes. In a nano-cave, the cave size becomes small in a porous material giving non-trivial capacitance, changing the behavior by up to 3 times the classic calculation This was discovered experimentally and only later explained by electrochemical simulations[9,10,11,12]. The results of both of these effects (quantum and electrochemical) give rise to a new regime of electrochemical behavior for nanosystems, qualitatively different from both by new well-studied dry nano-systems and classic large area electrochemical systems

Methods

Results

Conclusion