Understanding the anodic mechanism of a seafloor fuel cell

Graduation date: 2004Anoxic sediment overlain by oxic seawater establishes a voltage gradient on the order of 0.7-0.8V across the sediment-water interface. This study follows Reimers et al. (2001) and Tender et al. (2002) who reported the development of a seafloor fuel cell to harvest electrical energy from this potential difference. Prototype fuel cells were deployed for demonstration purposes in the Yaquina Bay estuary, Newport (Oregon, USA) and in a salt marsh near Tuckerton (New Jersey, USA) and were monitored during approximately seven months at either fixed current or fixed potential. Control cells with electrodes not connected to each other (open circuit) were deployed at each site near the prototype devices. The impacts of fuel cell processes on sediment solids and porewaters were studied by taking cores of sediment down to the surface of the anode (electrode embedded in sediment) of both active and control cells. Porewater profiles showed significant increases in sulfate and iron concentrations, but also sulfide depletion approaching the active anode. Solid-phase acid volatile sulfide and pyrite decreased significantly toward the anode. Fe(III) mineral phases did not appear affected by the presence of the fuel cell. Particulate organic carbon was not depleted significantly either. Electron microprobe analyses and SEM images revealed accumulations of sulfur and iron with Fe/S ratios