Electrolysis utilizing magnesium (Mg) electrodes can neutralize hydrogen sulfide (H2S) by leveraging the electrochemistry of magnesium hydride (MgH2) formation/decomposition, acting as a "shifting polarity" system where the anode and cathode roles can be reversed or managed to handle both sulfur passivation and hydrogen production.
Mechanism and Key Components:
Anode (Oxidation): Magnesium metal (Mg) acts as a sacrificial or rechargeable anode, oxidizing to (Mg2+) ions and releasing electrons.
Cathode (Reduction): (H2S) is reduced at the cathode, often requiring an alkaline medium (NaOH or Mg(OH)2) to dissolve (H2S) into hydrosulfide (HS-) ions, which then react with water to form dihydrogen (H2).
Neutralization of H2S : The generated (OH-) reacts with (H2S) to produce (HS-) and eventually elemental sulfur (S).
Shifting Polarity/Reversible System: Magnesium anodes are prone to surface passivation by (MgH2), (MgO), and (Mg(OH)2) in aqueous solutions. A "polarity shift" or alternating current (AC) electrolysis approach can break down this passivation layer:
Phase A: Mg acts as the anode, releasing ions and (H2) is produced.
Phase B: Polarity is reversed; the Mg electrode becomes the cathode, reducing the surface oxides/hydrides (Mg(OH)2/MgH2) back to active magnesium metal (Mg).
Advantages of this System:
Eco-friendly By-products: The process produces valuable elemental sulfur and high-purity hydrogen, rather than harmful sulfur oxides (SOx).
Energy Efficiency: Magnesium-based electrolysis can operate at lower potentials than conventional water electrolysis.
Removal: The system effectively removes (H2S) from waste streams while generating hydrogen.
Recent developments include using "chainmail" graphene-encapsulated catalysts on Mg or other metal foam to prevent sulfur passivation, which is the main inhibitor of efficiency in this process.
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[9] https://www. youtube.com/shorts/Zb4oo-mS_n0
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[11] https://www.pnas.org/doi/10.1073/pnas.2202884119
[12] https://pubs.acs.org/doi/10.1021/acs.energyfuels.0c01161