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Electrolysis of water performed by microsecond voltage pulses of alternating polarity has been used to generate nanobubbles in microscopic systems. These nanobubbles exhibit interesting and useful effects, but their production requires a high current density of >10 A/cm 2. Deposited platinum or gold electrodes cannot withstand these conditions for a long time. Titanium showed the best durability, although it also undergoes degradation. The mechanism of degradation differs from that in usual DC electrolysis and was not previously explored. In this paper, the wear of thin film titanium electrodes fabricated on a silicon substrate by surface micromachining is investigated. The electrodes are tested in the alternating polarity process of various frequencies and durations. They are oxidized during operation, but the spatial distribution and chemical composition of the oxide differ from those observed in normal electrolysis. The strongest oxidation occurs at the edges of the electrodes, while the central part is less involved. At a high frequency of voltage pulses (400 kHz) the electrodes are oxidized much less than at low frequency (50-100 kHz). The oxide grows due to misbalance between periodic oxidation and reduction processes. Internal mechanical stress generated due to oxidation causes degradation of the electrodes.

Microfluidic devices providing an accurate delivery of fluids at required rates are of considerable interest, especially for the biomedical field. The progress is limited by the lack of micropumps, which are compact, have high performance, and are compatible with standard microfabrication. This paper describes a micropump based on a new driving principle. The pump contains three membrane actuators operating peristaltically. The actuators are driven by nanobubbles of hydrogen and oxygen, which are generated in the chamber by a series of short voltage pulses of alternating polarity applied to the electrodes. This process guaranties the response time of the actuators to be much shorter than that of any other electrochemical device. The main part of the pump has a size of about 3 mm, which is an order of magnitude smaller in comparison with conventional micropumps. The pump is fabricated in glass and silicon wafers using standard cleanroom processes. The channels are formed in SU-8 photoresist and the membrane is made of SiNx. The channels are sealed by two processes of bonding between SU-8 and SiNx. Functionality of the channels and membranes is demonstrated. A defect of electrodes related to the lift-off fabrication procedure did not allow a demonstration of the pumping process although a flow rate of 1.5 µl/min and dosage accuracy of 0.25 nl are expected. The working characteristics of the pump make it attractive for the use in portable drug delivery systems, but the fabrication technology must be improved.

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Electrochemical actuators are promising candidates for implementation in various microfluidic systems, but they suffer from a very long response time due to slow gas recombination. Water electrolysis performed by short voltage pulses of alternating polarity (AP) reduces the response time by several orders of magnitude. This process, however, results in a fast degradation of electrodes. It is important to find a material, which is able to withstand the AP operation without significant degradation. In this work the electrodes made of six metals are fabricated and tested. The current flowing through the cell, the threshold voltage for the explosive operation, and the wear of the electrodes are analyzed and compared.