Observation of Remote Electroconvection and Inert-Cation Concentration Valley within Supporting Electrolytes in a Microfluidic-Based Electrochemical Device

The electrochemical system is playing an increasingly important role in the advanced technology development for drinkable water and energy storage. While the binary electrolyte has been widely studied, such as the associated intriguing interfacial instabilities, multi-component electrolyte is by far less known. Here, based on the classic Cu|CuSO₄|Cu electrochemical system, the effect of supporting electrolyte is systematically investigated by highlighting the inert cations. In an annulus microfluidic device, the suppression of a previously known electro-osmotic instability and the emergence of an array of the remote electroconvection along the azimuthal direction is found. A distinctive inert-cation concentration valley propagates radially outward at a speed limited by the electromigration velocity. Remarkably, the simultaneous visualization of spatiotemporal evolution demonstrates the correlation of the concentration valley and electroconvection at a microscopic level. The underlying physical mechanism of their correlation is discussed, and the scaling analysis agrees with experiments. This work might inspire more future work on the multi-component electrolyte, such as for the suppression of interfacial hydrodynamic instability and mitigation of dendrite growth, with the technological implications for water treatment and energy storage in batteries.