Concentration Cell Powered by a Chemically Asymmetric Membrane: Theory

Batteries are a key resource in the quest for sustainable energy.  Here theory is presented for a newly proposed type of electrochemical concentration cell that should contribute to this enterprise.  It utilizes ambient thermal energy to generate its concentration differential and, therefore, is self-charging.  The cell employs two electrolyte-filled chambers partitioned by a chemically asymmetric membrane, which drives anisotropic diffusion of electrolyte ions; the resulting concentration difference powers a concentration cell.  The asymmetric membrane is its novel and defining feature.  The concept governing this `asymmetric membrane concentration cell' is quite general and has been successfully demonstrated in the laboratory; numerical simulations further corroborate it.  In this study, the membrane's operation is validated by three theoretical approaches: (i) traditional equilibrium thermodynamics; (ii) balancing drift and diffusion current densities; and (iii) the time-independent diffusion equation.  The physical criteria for its operation are developed, its dimensionless variables are identified, and a physical instantiation suggested.  The cell's self-rechargeability should confer multiple advantages, including improved efficiency, economy, and compactness, thereby enhancing its energy sustainability.  Commonalities with other electrochemical systems  (e.g., liquid chromatography, metal corrosion, and solid state diodes) are also discussed.