Hydrogen sulfide (H2S)-assisted seawater splitting for green hydrogen production: A photocatalyst-free strategy for converting toxic waste into clean energy

Toxic hydrogen sulfide (H 2 S) from natural and industrial sources poses health risks. Thus, there is ongoing research on CO x -free hydrogen production from H 2 S. However, challenges like catalyst instability and high energy persist. In this study, we report the development of a photocatalyst-free approach for H 2 production through H 2 S dissolved seawater splitting. The presence of H 2 S in seawater enhanced H 2 evolution by over 4.5 times. The average hydrogen production rate over the duration of the experiment was 27.88 μmol L −1 min −1 using seawater (3.5 wt% NaCl) compared to 4.52 μmol L −1 min −1 in pure water. Results indicated that H 2 was generated through both HS – ions conversion and seawater splitting. HS – ions produce H 2 through one of three reaction pathways, each initiated by the photoexcitation of HS – , while the dissolved H 2 S species may enhance seawater splitting through possible interactions with NaCl that could be associated with observed morphological transformations. Further investigation revealed that while sacrificial agents enhanced H 2 production under N 2 atmosphere, they inhibited performance in the presence of H 2 S. Ethanol reduced H 2 yield by 44.02%, followed by methanol (54.68%) and glycerol (59.42%); likely due to competition for photon absorption, suppression of H 2 S solubility, or interference from byproducts. The effects of individual seawater ions were also examined. Notably, KCl produced the highest yield after NaCl at 8.91 μmol L −1 min −1 while MgCl 2 , CaCl 2 and Na 2 SO 4 produced significantly lower yields. SEM/EDX analysis showed that dissolved H 2 S interacts differently with seawater salts, with greater sulfur adsorption on NaCl, explaining the variation in performance. This study provides a sustainable method for producing H 2 from H 2 S-rich industrial waste in seawater, enabling a closed-loop cycle and reducing reliance on carbon-intensive hydrogen sources.