Continuously Activated Function of Aluminum in Galvanic Micro Arrays in Contact with Water

Abstract

Galvanic coupled arrays of Aluminum (Al) and Gold (Au) aligned in microgap has displayed high accuracy and sensitivity towards detection of invisibly small water droplets. With Al in moisture sensing chip, 1) formation of Al2O3 layer around Al and 2) decay of Al electrode with time, may interfere its overall activity. In this study, a continuous activation of Al electrode on the sensor chip was performed and investigated through electrochemical evaluation, output current measurement, and SEM observations. Further pH in its vicinity was simulated for ∼2 years. The results showed that a sensing chip exhibits almost steady output current throughout the period. At relatively high current density of 1.25 × 10−6 A.cm−2, obtained in the short circuit, anodic reaction on the Al electrode generates protons. This production of protons reduces the pH to ∼4, where Al2O3 and Al3+ formed on its surface could get dissolved. In addition, Al consumption in 100 ms, i.e. the time for one closed circuit corresponds to 2.26 × 10−17 g.A−1 s−1, which is negligible. The SEM images confirmed unchanged morphology of Al electrodes. The results support the long-term stability of accurate and sensitive sensor chip with galvanic array of Al and Au electrodes.