FeS and Ni-FeS, a co-precipitation method, also based on the literature, was used. In this work, mineral-formation fluids (Table ) were mixed in a 1:1 proportion to form the precipitates of Fe-S and Ni-Fe-S minerals. Then, the resulting suspension was separated by centrifugation and the precipitated mineral paste was used as an electron-conductive ink painted onto Fe electrodes.