Mimicking the microbial oxidation of elemental sulfur with a biphasic electrochemical cell

The lack of an artificial system that mimics elemental sulfur (S₈) oxidation by microorganisms inhibits a deep mechanistic understanding of the sulfur cycle in the biosphere and the metabolism of sulfur-oxidising microorganisms. In this article, we present a biphasic system that mimics biochemical sulfur oxidation under ambient conditions using a liquid|liquid (L|L) electrochemical cell and gold nanoparticles (AuNPs) as an interfacial catalyst. The interface between two solvents of very different polarity is an ideal environment to oxidise S₈, overcoming the incompatible solubilities of the hydrophobic reactants (O₂ and S₈) and hydrophilic products (H⁺, SO₃^2–, SO₄^2–, etc.). Furthermore, the interfacial AuNPs provide a catalytic surface onto which O₂ and S₈ can adsorb. Control over the driving force for the reaction is provided by polarising the L|L interface externally and tuning the Fermi level of the interfacial AuNPs by the adsorption of aqueous anions. Comparison of electrochemical measurements using a 4-electrode closed bipolar electrochemical cell and a L|L electrochemical cell confirmed that electron transfer reactions are possible between O₂, gold and S₈ in biphasic systems.