Using an electrically switchable composite of carbon and silicon dioxide, a research team at TU Darmstadt has, for the first time, selectively removed gases such as carbon dioxide, nitrogen, or argon from the gas phase – simply by applying an electrical voltage. The material stores the gases on its surface and releases them completely when the voltage is changed. The study opens up new perspectives for energy-efficient separation processes and has now been published in "Advanced Science."
Separating substances from one another is of central importance in science and technology. Separating liquids, for example, often requires a lot of energy, such as distillation and evaporation.
However, there are also gentler methods for separating substances in a targeted manner. These work by attaching substances (adsorbates) to a surface and then later detaching them. For example, in several steps, different gases can be captured (adsorbed) and released (desorbed) one after the other.
To realize adsorption and desorption in an energy-efficient manner, switchable materials and processes are required. For technological use, the switchable material must also be readily available. The switching process should be reversible and as resource-efficient as possible. For this purpose, electrical processes are the focus of application-oriented research. This process becomes particularly attractive when the required electrical energy can be provided largely from renewable sources.
A research team led by doctoral candidate Silvio Heinschke and Professor Jörg J. Schneider from the Mesoscopic Chemistry group in the Department of Chemistry at TU Darmstadt has succeeded for the first time in directly adsorbing carbon dioxide (CO₂), nitrogen (N₂), or argon from the gas phase by applying a low electrical voltage to a material (adsorbent). This adsorbent consists of carbon (coal) and silicon dioxide (sand). Later, these gases can be released from the adsorbing material in a controlled and complete manner by removing the voltage. The results were published in Advanced Science.
The trick here is to create interfaces in the material measuring just a few micrometers. These interfaces arise between the electrically conductive carbon and the dielectric, i.e., insulating, silicon dioxide. The mixture (composite) of the two materials is necessary and crucial for the adsorption/desorption behavior now described for the first time.
Between the numerous carbon and silicon dioxide interfaces in the composite, inhomogeneities, i.e., field gradients, are generated by electrical charging. In these fields, gas molecules such as CO₂, N₂, or argon become slightly electrically charged or polarized and then adhere to the carbon surface.
Adsorption is influenced by the multipoles in the gas molecules. These exhibit different charge distributions and polarizabilities in the electric field. The resulting binding of the gases to the adsorbent is fully reversible. Thus, by switching the electric field on and off, a voltage-induced swing between the charging and discharging from the gas phase and the composite surface can be generated.
This principle should, in principle, be feasible for all gases with high polarizability. Based on this, the separation of gas mixtures by electrically controlled swing adsorption/desorption also appears realistic in the future.
original publication
Interface Controlled Electric Field Swing Adsorption
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