(297i) High Pressure-to-Voltage Energy Conversion Efficiency in Nanofluidic Channels

The electrokinetic behavior of nanofluidic devices is dominated by the electrical double layers at the device walls.  In many contemporary nanofluidic devices, the surface charge of the channel walls is large enough that the nonlinear coupling between the “simple” interactions between the wall and ions gives the device novel properties that change with ion type and concentration.  The simplest nanofluidic device geometry is the channel with two charged walls separated by ~100 nm.  Here, it is proposed that the layering of large ions at the wall/liquid interface of nanofluidic channels (due to wall-ion and ion-ion correlations) can be used to achieve high efficiency (possibly >50%) in the conversion of hydrostatic energy into electrical power.  Large ions tend to produce peaks and troughs in their concentration profiles at charged walls, producing high concentrations far from the walls where the ions’ pressure-driven velocity is high.  This increases the streaming conductance and the energy conversion efficiency.  The results are computed with density functional theory of fluids, a theory that includes ion-ion correlations in a way this both computationally efficient and thermodynamically accurate.