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Evaporation-driven spontaneous capillary flow presents a promising approach for driving electrolytes through electrically charged channels and pores in electrokinetic energy conversion devices. However, there are no literature reports of detailed flow visualization in these systems and/or experimental observations relating the liquid velocity and evaporation rate to the generated voltage and current. In this manuscript, we describe such a visualization study for a glass channel based electrokinetic energy conversion device with one of its channel terminals left open to ambient air for facilitating the evaporation process. Fluorescence microscopy was used to measure the liquid velocity in the electrokinetic energy conversion channel by observing the advancement of an electrolyte solution dyed with a neutral tracer. The accumulation of the same dye tracer was also imaged at the open terminal of this glass conduit to estimate the rate of solvent evaporation, which was found to be consistent with the flow velocity measurements. Additionally, an electrochemical analyzer was employed to record the electrical voltage and current produced by the device under different operating conditions. The highest electrical power output was derived in our experiments upon flowing de-ionized water through a 1 μm deep channel, which also produced the fastest liquid velocity in it. Moreover, the energy conversion efficiency of our device was observed to increase for shallower channels and lower ionic strength electrolytes, consistent with previous literature reports on electrokinetic energy conversion platforms. 

Abstract The broadening of analyte streams, as they migrate through a free‐flow electrophoresis (FFE) channel, often limits the resolving power of FFE separations. Under laminar flow conditions, such zonal spreading occurs due to analyte diffusion perpendicular to the direction of streamflow and variations in the lateral distance electrokinetically migrated by the analyte molecules. Although some of the factors that give rise to these contributions are inherent to the FFE method, others originate from non‐idealities in the system, such as Joule heating, pressure‐driven crossflows, and a difference between the electrical conductivities of the sample stream and background electrolyte. The injection process can further increase the stream width in FFE separations but normally influencing all analyte zones to an equal extent. Recently, several experimental and theoretical works have been reported that thoroughly investigate the various contributions to stream variance in an FFE device for better understanding, and potentially minimizing their magnitudes. In this review article, we carefully examine the findings from these studies and discuss areas in which more work is needed to advance our comprehension of the zone broadening contributions in FFE assays.