Hydrogen sulfide (H2S) is a major hazardous waste byproduct in both municipal wastewater treatment and industrial petrochemical-related processes. This project explored a new route to recycle it by first absorbing it in a caustic scrubber (H2S + NaOH --> NaHS + H2O) and then oxidizing NaHS back to NaOH in a photoelectrochemical cell using solar energy. The photoelectrochemical cell produces hydrogen at the cathode and polysulfide ions at the photoanode. The polysulfide ions yield sulfur in another cell. This novel concept was demonstrated in a photoelectrochemical system with separated cathodic half-cell that produced hydrogen and anodic cell that produced oxygen in the absence of hydrogen sulfide (i.e. in NaOH solution) and polysulfide ions in NaHS mixed with NaOH. In light of these promising results, further work should be done to assess the potential benefits of the photoelectrochemical route over existing technologies for hydrogen sulfide recycling.
