Hydrogen production from oxidation of coal slurries assisted by ferric ions

A novel method of hydrogen production from oxidation of coal slurries using the mutual transformation of Fe³⁺ and Fe²⁺ was studied. At the first step, in a boiling kettle coal slurries are oxidized by Fe³⁺ into Fe²⁺. Then Fe²⁺ is oxidized in an anode chamber and hydrogen is produced in cathode chamber. The two steps are combined to form a cycle to produce hydrogen. Nine cycles were performed at constant voltage (1 V) and the current densities and accumulated electric quantities at each cycle were investigated. The coal samples before, during and after reaction were analyzed with scanning electron microscope (SEM), BET specific surface area, thermal gravity (TG) and Fourier transform infrared spectrum (FT-IR). The results show that hydrogen production of "two-step" cycle processes has a higher reaction rate. The initial current density is about 60 mA/cm², while that of traditional "one-step" process is usually less than 10 mA/cm². The characterizations give a clear understanding on the changes of coal particles in morphology, structure and composition during the cycles, and also reveal the reaction mechanism of mutual transformation between Fe³⁺ and Fe²⁺.