Hydrogen Production via Electrochemical Oxidation of Aqueous Ferrous Sulfite Solution

  • Dr Cunping Huang, University of Central Florida, Florida Solar Energy Center, United States
  • Dr Clovis Linkou, University of Central Florida, Florida Solar Energy Center, United States
  • Mr Franklyn Smith, University of Central Florida, Florida Solar Energy Center, United States
  • Mr Karthikeyan Ramasamy, University of Central Florida, Florida Solar Energy Center, United States
  • Dr Ali T-Raissi, University of Central Florida, Florida Solar Energy Center, United States
  • Dr Nazim Murradov, University of Central Florida, Florida Solar Energy Center, United States

    • Removal of hydrogen sulfide (H2S) is important in the natural gas processing as it corrodes pipelines and deactivates metal-based catalysts used in steam methane reformation plant. There are a number of known H2S removal processes practiced commercially, or in bench scale demonstration. Based on the H2S reactions involved, these technologies can generally fall into two classes:

    Partial oxidation: H2S + ½O2 = S + H2O ΔHo 298K = -265.2 kJ/mol
    Decomposition: H2S = ½S2 + H2 ΔHo 298K= 79.9 kJ/mol

    Partial oxidation of H2S generates only elemental sulfur and heat but no hydrogen. One example of partial oxidation involves the use of Fe2+/Fe3+ redox system can be envisioned as follows:

    2Fe3+(aq) + H2S(g) = 2Fe2+(aq) + S(s) + 2H+(aq)
    2Fe2+(aq) + ½O2(g) +H2O(l) = 2Fe3+(aq) + 2OH-(aq)

    Typical anions used above include Cl- and SO42- or organic reagents, chelates, cyanide, etc. At Florida Solar Energy Center, we have developed a novel process based on Fe2+/Fe3+ redox pair for the decomposition of H2S into sulfur and H2:

    Fe2(SO4)3(aq) + H2S(g) = 2FeSO4(aq) + H2SO4(aq) + S(s) (Chemical absorption)
    2FeSO4(aq) + H2SO4(aq) = Fe2(SO4)3(aq) + H2(g) (Electrolytic regeneration)

    This paper presents results for the hydrogen production from electrolysis of aqueous FeSO4 solution with focus on the electrolyzer design. Results have shown that the electrolysis of FeSO4 aqueous solution is highly efficient process with coulometric efficiency as high as 100% at 1.0 V or lower. The effect of reaction conditions, such as pH, FeSO4 concentration, and temperature, is also discussed in detail.