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

Abstract

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.