The Solution to Electrode Surface Fouling
Electrode surface fouling is a serious problem in many electrochemical production processes and in electrochemical sensors. Electrode fouling can affect the performance and energy efficiency of an electrochemical cell. Ultrasonication is an effective means to avoid and remove electrode fouling.
Electrode fouling reduces the physical contact of the electrolyte with the electrode for electron transfer to and hence it reduces the electrochemical reaction speed. Often the fouling agent adheres to certain structural features on the electrode surface as a result of hydrophilic, hydrophobic, or electrostatic interactions between the fouling agent and the electrode surface.
Antifouling methods include surface modification or coating with polymers or carbon-based materials, such as carbon nanotubes or graphene, due to their large surface area, electro-catalytic properties, and fouling resistance. Alternatively, metallic nanoparticles can have antifouling properties combined with electro-catalytic properties and high electrical conductivity.
Ultrasonic mechanical agitation is an alternative antifouling method.
Ultrasonic agitation for antifouling uses high-frequency, high-intensity sound waves in a liquid to facilitate or enhance the removal of fouling agents from surfaces submerged in an ultrasonically activated liquid. Ultrasonic electrode surface cleaning is a technology unique in its ability to remove fouling agents from electrode surfaces. Ultrasonic cleaning technology is able to penetrate and clean any wetted electrode surface, including blind holes, threads, surface contours.
Demands for improved electrode surface cleanliness have driven the development of ultrasonic agitation technology. Today it is possible to agitate electrodes mechanically at ultrasonic frequency or to agitate the liquid near the electrode for indirect electrode surface cleaning.
Indirect Electrode Surface Antifouling
In the indirect antifouling of electrode surfaces, the ultrasonic power is delivered to the liquid near the electrode. This liquid adsorbs the ultrasonic power and transmits a fraction of this power to the electrode surface, where the resulting ultrasonic cavitation removes fouling layers. In general, this indirect method is “line of sight” in nature; that is, there must be direct access to the contaminated surface for it to be effective.
Electrode fouling describes the passivation of an electrode surface by a fouling agent that forms an increasingly impermeable layer on the electrode. Often, the fouling agent is a byproduct of the electrochemical reaction.
Direct Electrode Surface Antifouling
Hielscher Ultrasonics offers a unique ultrasonic design to agitate electrodes directly. In this design, the ultrasonic vibrations are coupled directly into the electrode. Therefore the ultrasonic power is delivered to the wetted electrode surface, where the surface acceleration and collapsing cavitation bubbles in contact with a surface provide a high pressure jet of fluid against the surface. Ultrasonic jetting is good method to avoid and remove fouling layers.
Facts Worth Knowing
Other possible effects of ultrasonic agitation upon an electrochemical system include:
- improve hydrodynamics and mass transport;
- affect concentration gradients and switching of kinetic regimes with effect on mechanism and reaction products;
- sonochemical activation of reactions of intermediate species that have been generated electrochemically; and
- sonochemical production of species that react electrochemically in conditions where the silent system is not electrochemically active.
Types of Electrode Fouling
Fouling resulting from hydrophilic interactions tends to be more reversible than fouling resulting from hydrophobic interactions. Electrodes with more hydrophobic surfaces, such as carbon-based electrodes can promote fouling possessing hydrophobic components, such as aromatic compounds, saturated or aliphatic compounds, or proteins. Biological macromolecules, such as proteins and other biological materials, cells, cell fragments, or DNA/RNA can cause electrode surface fouling, too.