Abstract
A proof-of-concept electrochemical analog for a Carnot cycle is developed using a capacitive mixing (CapMix) engine to extract electrical energy from a salinity gradient. Here, temperature is allowed to vary to assist in the development of such a cycle. The Gouy-Chapman-Stern model for the electrochemical double layer (EDL) reveals theoretically that approximately a 50 mM concentration difference can be used if the initial concentration is 100 mM. Under transient conditions, this range was further limited to lower than 10 mM, but revealed some interesting trends in the current, flow rate, and heat input control: Flow should nearly be stopped when the cell is not charged or discharged, heat transfer should account for variations in the surrounding air temperature, and additional discharging is necessary to return to the initial concentration. Approximately 0.25 kJ of electrical work was extracted from the cycle, accounting for approximately 10% of the available energy from the mixing process. However, while the cycle operates as a Carnot analog electrochemically, thermodynamically over 800 kJ of heat is required to drive the temperature differences, so this heat needs to be managed carefully when realistic time and geometric parameters are introduced.
