Long Life Electrochemical Diodes for Continuous Electrowetting

Abstract

The rate of electrochemical reactions in some systems varies with the polarity of the overpotential on the working electrode, introducing diode-like behavior at the electrode/electrolyte interface. However, with repeated bipolar cycling, the electrochemical current damages the electrodes. We have connected electrochemical diodes in series with opposing polarities to reduce the diode current while charging a capacitive circuit. We have previously used this capacitive circuit arrangement to actuate aqueous droplets continuously using the electrowetting (EW) effect. In this study, the performance of electrochemical diodes under repeated voltage cycles is investigated. Aluminum and titanium electrodes in contact with three electrolyte solutions (0.1 M citric acid, 0.1 M Na2SO4 and 0.1 M NaOH) are employed. The diode behavior of electrochemical systems with single diodes and diode pairs is compared. A coefficient of continuous electrowetting (CEW) actuation (referred to as actuation coefficient) is introduced. Actuation coefficient varies between zero (no actuation) and one (equivalent to grounded droplet actuation at the same voltage. Experimental results how that titanium maintains higher actuation coefficients (0.6 −0.8) than aluminum (0.6). The actuation coefficients of titanium increase over the first trials and remain stable under alternating −50 V and +50 V inputs for 2000 trials (experiment duration).