Electrokinetic energy conversion efficiency in square nanofluidic channels assessed by monitoring streaming potential and current

The application of nanofluidics systems involving channel sizes in the range of 1–1000 nm to energy conversion using the electrokinetic effect has received much attention. However, electrokinetic and hydrodynamic power conversion efficiencies have thus far been investigated primarily using theoretical approaches other than a few experimental studies based on nanopores or plate nanochannels. To date, there have been no reports of experimental assessments of square nanochannels due to the difficulties involved in nanochannel fabrication and the control of flow and surface states. The present study examined the electrokinetic energy conversion efficiency in size-regulated square nanochannels by monitoring the streaming current and potential, both of which were proportional to the applied pressure. Using nanochannel size data and previously determined liquid viscosities in such nanochannels, zeta potential, hydrodynamic resistance, figure of merit and maximum conversion efficiency data were obtained. The maximum conversion efficiency in square nanochannels was found to be similar to or greater than that in plate nanochannels. The maximum conversion efficiency was also increased with decreases in either the KCl concentration or the nanochannel size. The maximum conversion efficiency in square nanochannels was shown to be increased by decreasing the nanochannel size and a maximum value of 3.5 ± 0.9 % was obtained. Electrokinetic power was also increased by increasing the number of nanochannels and normalized maximum electrokinetic power density values were calculated. The measured results and discussion based on the unique properties of nanochannels provide a new and important approach to understanding the fluidic and electrokinetic phenomena occurring in nanochannels.