Generation of electricity and illumination by an environmental fuel cell in deep-sea hydrothermal vents.

Public interest in the generation of power by alternative energy sources in the ocean beyond fossil fuels and nuclear energy has increased in recent years. Power generation in the ocean is also of great interest for the inexpensive and efficient supply of electricity for the survey and exploration of submarine resources. Deep-sea hydrothermal vents are environments that discharge crustal hydrothermal fluids, geologically driven by magmatism and geochemically processed by the high temperatures of rock–seawater interactions and alterations. Hydrothermal fluids enriched with reduced chemicals are mixed with oxidative chemicals in seawater in the vicinity of deep-sea vents. The steep chemical slope between the hydrothermal fluids and ambient seawater has the potential to generate electricity. Therefore, it is likely that electricity is generated in situ between hydrothermal fluids (HF) and seawater (SW), which can be promoted and confirmed by deployment of artificial electrodes and a conductor. Herein, we show the development of an HF–SW fuel cell for deep-sea hydrothermal vents. During the Integrated Ocean Drilling Program (IODP) in 2010, several artificial hydrothermal vents were created by the drilling of wells in the Iheya North hydrothermal field of the Okinawa Trough, Japan. One of the artificial hydrothermal vents (C0014G) had a vigorous discharge with a high fluid temperature (Tmax= 309 8C) at a water depth of 1053 m. In this work, seafloor electrochemical analyses were conducted in the C0014G vent using a remotely operated vehicle (ROV) equipped with a deep-sea potentiostat/galvanostat system (D-Pote), which was covered with an anti-pressure housing and controlled by an onboard computer through data communication. First, the oxidation–reduction potential (ORP) of the ambient seawater and hydrothermal fluids was measured (Figure 1). The average temperature and ORP of the ambient seawater were approximately 4 8C and + 478 mV, respectively, versus the standard hydrogen electrode (SHE), while those of the hydrothermal fluids were approximately 309 8C

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