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ERC

IONACES Report Summary

Project ID: 291543
Funded under: FP7-IDEAS-ERC
Country: France

Final Report Summary - IONACES (Understanding ion transport in nanoporous carbons; application to energy storage and sustainable development)

Electrochemical Double-Layer Capacitors (EDLC) are promising devices for clean energy storage applications. In EDLCs, the charges are stored electrostatically at the electrolyte / electrode interface, which confers them high power and cycling capabilities. Recent results showed that high capacitive performances could be obtained when the carbon pore size was set smaller than the solvated ion size. The origin of this capacitance increase was still unclear despite important modelling efforts achieved by many research groups.

First, we provided the first quantitative picture of the structure of an ionic liquid adsorbed inside a real microporous carbon electrodes (CDCs) using Molecular Dynamics simulations. We showed how the separation of the positive and negative ions occurs inside the porous electrodes, yielding to much higher capacitance values than with simpler electrode geometries. We also showed that both a desolvation and a local charge stored on the electrode increase with the degree of confinement. More, the ion desolvation was forced when external electric field was applied (under polarization), and we also showed that ions could access more confined pores. Those results ruled out the traditional view of the Gouy-Chapman model used to describe the double layer formation in nano-sized carbon pores. We also designed specific advanced characterization techniques to experimentally assess the partial desolvation. Using Electrochemical Quartz Crystal Microbalance (EQCM), we measured the extent of desolvation when ions were entering nano-sized pores and found that ions loose up to 60% of their solvent shell in acetonitrile. Combining EQCM together with in-situ Nuclear Magnetic Resonance experiments, we also showed for the first time a different ion adsorption mechanism depending on the electrode polarity: counter ion (cation) adsorption at the negative electrode and ion exchange at the positive one under polarization.
Those results have been used for two applications.

First, we prepared the first micro-supercapacitor directly integrated on Si wafers, by preparing nanoporous carbons with controlled pore size less than 1 nm from the chlorination of TiC thin films. Our on-chip micro-supercapacitors compete with the best carbon-based devices reported to date and the process is fully compatible with the semi-conducting industry.

Last but not least, we developed a new, potentially low-cost and scalable capacitive deionization system based on the use flowable carbon electrodes for water desalination. The performance and desalination efficiency of flowable carbon electrodes was assessed electrochemically, first in a static mode, showing about 70% Na,Cl adsorption efficiency. This promising result suggests that, upon further with design and material optimization, this concept may yield to a high electro-sorption capacity system capable of meeting and exceeding performance of traditional CDI systems.
Those results could never have been obtained without the support of the ERC grant.

Reported by

UNIVERSITE PAUL SABATIER TOULOUSE III
France
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