DEVELOPMENT OF AN ALUMINUM SEA-WATER BATTERY FOR SUBSEA APPLICATIONS

There are two modes of operation for an aluminium/water battery: use o f hydrogen-evolving or oxygen-reduction cathodes. In the first case, t he current density is approximately 10 mA cm-2 at 0.5 V. This leads to significant increase of pH and deposition of Ca/Mg(OH)2 at the cathod e, leading to sharp decrease in battery performance. On the other hand , in the oxygen-reduction mode, the current density is approximately 0 .1 mA cm-2 at 1.4 V, because of the low concentration of O2 in sea-wat er. Long-term tests of an Al/water battery using Teflon-bonded Co3O4/C oxygen reduction cathodes in Brightlingsea Harbour, Essex, over a tes t period of 70 days have shown that the performance of this battery is stable and that it is possible to increase its performance by means o f multi-cathodes on either side of the anode. A conceptual design show s that such a battery has an energy density of 1008 Wh kg-1 over an op erating period of one year, significantly higher than all the conventi onal primary batteries considered for use in sub-sea environments.