The optimization of Ag/Ag2S electrode using carrier electroplating of nano silver particles and its preliminary application to offshore Kueishan Tao, Taiwan

Eutrophication-induced ocean acidification is causing a dramatic ecologic change in the coastal ocean. A more acidic ocean would lead to more volatile H2S in the coastal ocean, especially in the area where shallow hydrothermal vents exist. Therefore, the early detection of H2S and its associates is needed. In this study, the preparation method for and the detection limit of an Ag/Ag2S electrode were optimized by coating the electrode with micro-scale to nano-scale silver particles. The size of the silver particles was dependent on the electroplating power used to produce them: (1) direct current power made micrometer scale silver particles, and (2) direct current carrier power made nano-scale silver particles. As a result, the detection limits of [S2−] of the Ag/Ag2S electrode made using direct current and direct carrier current were improved to 1×10−5 mol L−1 and 1×10−7 mol L−1, respectively. Such improvements were mostly due to the fact that nano silver particles have larger surface area and higher surface energy. The Ag/Ag2S electrode made by direct carrier current method was then mounted to a multi-parameter sensor (including a pH and an Eh electrode) used to search of new hydrothermal vents near the Kueishan Tao in May, 2011. A new hydrothermal vent was discovered based on pH, Eh and H2S anomalies at three depths. A clear [S2−] signal anomaly was observed from the top sensor indicating the dispersive pattern of the hot fluid near this shallow vent site. This could also provide additional information on the dispersion pattern of anthropogenic pollutants in the coastal ocean.