Biochar-Assisted Iron-Mediated Water Electrolysis Process for Hydrogen Production

The biochar-assisted water electrolysis process for hydrogen gas production is reported. The H₂ generation is performed in a divided electrolysis cell in which the hydrogen evolution reaction occurs on a cathode and ferrous iron oxidation on an anode. Electrochemically produced Fe(III) species are reduced back to ferrous form in a reaction with biochar concentrated in a packed-bed column through which an acidic anolyte (FeCl₃) solution is continuously recirculated. During the operation of the proposed process with commercial charcoal, the oxidation of carbon resulted in an accumulation of oxygen-containing groups on the carbon surface that leads to charcoal deactivation. Thermal treatment of the charcoal at 250, 350, and 450 °C in a nitrogen atmosphere resulted in reactivation of carbon, and the best results (≈80% reactivation) were achieved after 3 h of treatment at 450 °C. Nine successful cycles of electrolysis-charcoal regeneration were performed in this study. A ≈98% current efficiency for hydrogen production was achieved at a current density of 50 mA/cm². Much higher current densities can be obtained using the proposed technique as the anodic process of ferrous iron oxidation is decoupled from the carbon oxidation process. The CO₂ production rate achieved in this study was up to 98% of a stoichiometric value proposed for the iron-mediated carbon-assisted water electrolysis process.