Electro deoxidation process for producing FeTi from low grade ilmenite Tailoring precursor composition for hydrogen storage

Abstract

FeTi is one of the earliest known hydrogen storage materials. The gravimetric storage and volumetric storage density are 1.8 wt. % and 120 kg/cm3, respectively. The volumetric storage density is almost twice that of liquid hydrogen, hence it can be a candidate suitable for safely storing hydrogen in stationary applications. Additionally, the source material of FeTi, Fe and Ti oxides, are abundantly available in nature. The major challenge is the cost-effective production of single-phase FeTi in scale. It is generally produced by extraction of individual Fe and Ti metals from their respective oxide precursors, followed by vacuum arc melting or mechanical alloying of extracted metals. This makes the process inefficient, especially because Ti extraction from its oxide is energy-intensive. Further, one ends up with a multi-phase material consisting of FeTi along with Fe2Ti. The storage efficacy of FeTi with Fe2Ti is lower compared to single-phase FeTi. newlineIn this dissertation, to circumvent the primary Ti production, an attempt was made to utilize ilmenite (FeTiO3) as a precursor for FeTi production via electro-deoxidation process. In this process, the precursor, i.e., compacted oxide pellet, is electro-deoxidized to its metal constituents in molten CaCl2 electrolyte. Similarly, FeTiO3 was electro-deoxidized to FeTi. The results show that phases present in electro-deoxidized pellet and hence the hydrogen storage capacity is dependent on the precursor composition. The Fe:Ti atomic composition ratio of commercial-grade ilmenite is not 1:1, and generally the atomic % of Ti is lower than Fe. Hence, electro-deoxidation of ilmenite with low Ti content (low-grade FeTiO3) results in the formation of a two-phase material consisting of FeTi and Fe2Ti. This two phase material as expected showed lower hydrogen storage capacity. To, analyze the role of Fe2Ti, single-phase Fe2Ti was synthesized by mechanical alloying of Fe and Ti powders. Hydrogen storage analysis of single-phase Fe2Ti showed that, it cannot store hydrogen.