Development of a seawater battery for deep-water applications

Dissolved-oxygen seawater batteries rely on the corrosion of a reactive metal anode and the reduction of oxygen at an inert cathode to generate a potential of about 1 V when immersed in seawater. Because oxygen is not very soluble in seawater, such batteries are characterized by small cathodic current densities and are therefore most suitable for long-term low-power applications. A number of batteries have been built recently using sophisticated electrodes. The objective of this study was to evaluate the feasibility of building a seawater battery using cheap readily-available materials. The results show that magnesium anodes outperform aluminum. Although the cathodic current densities achieved in this study are markedly lower than reported previously, cathodes composed of copper (or stainless-steel) mesh perform reasonably well and facilitate the design of compact batteries with an open structure and large cathodic areas. Deep- and shallow water tests show that a battery occupying 1 m3 could produce 5 W for a year or more in oxygen-saturated waters and 1–2 W in the oxygen-starved waters of the North Pacific seafloor. The energy density of such a battery including the flotation necessary for optimal performance and recovery is estimated to be 150–400 Wh kg−1.