Improving the performance of the fast electrochemical actuator

Abstract

Microfluidic systems require a compact actuator with low power consumption and high integration capability to drive pumps and valves. Electrochemical devices meet these criteria, but long time needed to terminate the gas makes them rather slow. Recently an actuator with a millisecond response time was demonstrated. A series of short voltage pulses of alternating polarity (AP) applied to the electrodes generates nanobubbles in the chamber. They push the flexible membrane up, and disappear quickly due to spontaneous combustion of hydrogen and oxygen in nanobubbles. However, degradation of the electrodes suppresses the gas production and reduces the stroke in few minutes. In this work the methods to improve performance of the fast actuator are proposed. The design of electrodes plays an important role. In addition to the surface area, the distribution of nanobubbles significantly affects the membrane deflection. The concentric electrodes provide the largest stroke due to a low resistance of the cell and well localized cloud of nanobubbles, but a high current density leads to a rapid oxidation of titanium electrodes. The rectangular structures ensure better long-term stability and lower power consumption per unit deflection. Increasing the surface area of the electrodes by changing the deposition conditions enlarges the stroke by 25–70 % depending on the design, but does not prevent reduction of the performance with time. A new operation regime, in which single polarity (SP) pulses are applied to the electrodes between the series of AP pulses, recovers the membrane deflection to the initial level or even larger. A possible underlying mechanism is the cathodic reduction of titanium. A large stroke can be maintained without increasing the power consumption during at least one hour, but it requires tuning of the amplitude of SP pulses.