Charge transport at nanoscale solid-solution interfaces plays important roles in energy technology. Many interesting charge transport phenomena emerge at nanostructured electrodes and nanochannels devices. Built upon the steady-state ion current rectification (ICR), which displays a non-linear response of current with applied potential,1 we recently reported that dynamic ion transport through asymmetric nanopore devices to be history-depend, specifically dependent on the previous ionic distribution at the transport limiting nano-interface region.2 Energy applications require the elucidation of fundamental mechanism, which has not been established. Here we present proof-of-concept experiments for the conversion of chemical energy in the format of salinity gradient into electrical energy and vice versa.3 Basic experimental design includes a conical nanopipette device connecting two solutions either at same electrolyte concentrations, or at different electrolyte concentrations. In the latter case, the asymmetric concentration establishes salient gradient between the tip and bulk solutions. The diffusion through the nanotip will be inevitably be affected by the local electrical field localized at substrate-solution interfaces. A scanning triangular waveform is applied to control the ion migration. The measured current signal in cyclic voltammetry reflects the total contributions of migration and diffusion, both affected by the surface electrical field. A stable non-zero cross-point that separates both normal capacitive behavior and negative capacitive behavior is observed. Theoretical model is proposed to explain the physical meaning of those interesting I-V features. Contributions of dynamic ionic transport from bias potential, concentration gradient and surface effect are correlated accordingly. The cross point is proposed as characteristic for individual nanodevice to evaluate the efficiency of power generation. Enhanced power generation is further achieved by adjusting pH and adopting different electrolyte systems, which demonstrate great potentials to achieve higher efficiency in green energy technology.

History-dependent electrical power generation of conical nanopipette under salinity gradient

247th National Meeting (2014)

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