In a recent opinion article, marine scientists and electrochemists listed a number of reasons why it's unlikely that metallic nodules on the deep seafloor could produce oxygen in total darkness.
More than 4,000 meters below the surface of the Pacific Ocean, the water is permanently black and near freezing. No sunlight ...
For decades, school textbooks have explained that oxygen on Earth is mainly produced through photosynthesis, a process that depends on sunlight. Plant.