Presentation Information
[S2-08]Investigation of Thermoelectric Conversion Mechanisms Mediated by Sulfide Mineral Network Structures in Seafloor Hydrothermal Vents
*Kentaro Toda1, Atsushi Okamoto1, OTGONBAYAR DANDAR1, Yoshinori Sato1, Ryosuke Oyanagi1, Tomonori Ihara2, Tatsuo Nozaki3,4 (1. Tohoku Univ., 2. TUMSAT, 3. Waseda Univ., 4. Tokyo Univ.)
Keywords:
Seafloor Hydrothermal Vents,Sulfide Chimney,Thermoelectric Conversion,Digital Twin,Rock-Life Interactions
Seafloor hydrothermal vents occur in island arcs, back-arc basins, rift zones, and along mid-ocean ridges. Sulfide chimneys formed by mixing hydrothermal fluids with seawater support unique ecosystems independent of sunlight. Electron transfer from reducing hydrothermal fluids to oxidizing seawater through sulfide chimneys has been proposed as one of their energy sources (Yamamoto et al., 2023). Sulfide chimneys consist of minerals with contrasting electrical conductivities, ranging from highly conductive pyrite, chalcopyrite, and galena to nearly insulating sphalerite (Okamoto et al., 2026). However, the three-dimensional mineral network controlling bulk electrical and thermal transport has remained poorly constrained. In this study, X-ray computed tomography (X-ray CT) and numerical simulations based on digital twin models were applied to sulfide chimney samples from the Okinawa Trough to investigate the relationship between mineral connectivity and thermoelectric conversion.
The samples were classified into three mineralogical groups representing different growth stages. X-ray CT revealed that ~97% of the pore space in sphalerite-rich chimneys was interconnected. In late-stage samples, ~100 μm-thick chalcopyrite films precipitated preferentially along pore walls, forming a continuous network. Transport simulations showed that the chalcopyrite network increased the bulk electrical conductivity by up to ten orders of magnitude compared with pure sphalerite, whereas the bulk thermal conductivity changed only slightly (16.0 to 12.1 W m-1 K-1). Consequently, the thermoelectric performance increased by up to eight orders of magnitude.
These results suggest that interconnected chalcopyrite networks create efficient electrical pathways while preserving the temperature gradient required for thermoelectric conversion. Electron transport through chimney walls is therefore likely controlled by the connectivity of highly conductive minerals. Furthermore, the thermoelectromotive force generated by these networks may act as a local overpotential, promoting redox reactions at chimney surfaces. Such a mechanism could contribute to electrochemical reactions requiring substantial overpotentials, including the reduction of CO2 to CO under seafloor hydrothermal conditions.
The samples were classified into three mineralogical groups representing different growth stages. X-ray CT revealed that ~97% of the pore space in sphalerite-rich chimneys was interconnected. In late-stage samples, ~100 μm-thick chalcopyrite films precipitated preferentially along pore walls, forming a continuous network. Transport simulations showed that the chalcopyrite network increased the bulk electrical conductivity by up to ten orders of magnitude compared with pure sphalerite, whereas the bulk thermal conductivity changed only slightly (16.0 to 12.1 W m-1 K-1). Consequently, the thermoelectric performance increased by up to eight orders of magnitude.
These results suggest that interconnected chalcopyrite networks create efficient electrical pathways while preserving the temperature gradient required for thermoelectric conversion. Electron transport through chimney walls is therefore likely controlled by the connectivity of highly conductive minerals. Furthermore, the thermoelectromotive force generated by these networks may act as a local overpotential, promoting redox reactions at chimney surfaces. Such a mechanism could contribute to electrochemical reactions requiring substantial overpotentials, including the reduction of CO2 to CO under seafloor hydrothermal conditions.