Advancement and Prospective of Hydrogen Generation from Hydrogen Sulfide Via Electrolysis Decomposition Approaches

Abstract Hydrogen sulfide (H2S) is known as a poisonous gas associated with oil production. It is vital for sustainable oilfield development to handle H2S effectively and convert it into highly-valued products and remove simultaneously the environmental pollutant. Electrolysis decomposition of H2S is one of promising and key technologies in this field as it can utilize water as a media to convert H2S to hydrogen (H2) and elemental sulfur (S). In this review, it summarizes the technology development in electrolysis decomposition of H2S by means of direct and indirect electrolysis approaches since 1980s. The emphasis is on the research attempts in the electrolysis to overcome the main hindrances and to reduce power consumptions. It includes the technical schemes, setups, conditions, and voltage consumptions. By critical reviews of the technologies, it presents the prospective in technology development from laboratory research to small scale application. It has been long realized that the energy consumption of direct electrolysis decomposition of H2S is much lower than that of water electrolysis decomposition. H2S in aqueous solution can be directly decomposed to produce H2 at the cathode by reduction reaction and S at the anode by oxidation reaction. Although high-quality H2 can be produced at the cathode, the accumulative aggregation of S on the anode surface results in serious passivation that ceases the overall electrolysis process. Many efforts were made to modify the electrolysis conditions to improve the electrolysis efficiency. On the other hand, indirect electrolysis schemes have been developed by 2 oxidation-reduction electrolysis reactions using specific redox couples. This scheme is more operationally feasible since it avoids anode passivation and S is produced by the oxidation step and separated before the electrolysis step. Some small-scale pilots presented efficient production of H2 and S at low power consumption of 2.0 kWh/Nm3-H2 compared to the power consumption of 4.5 kWh/Nm3-H2 for water electrolysis. In addition, other route using metal as cathode has been developed which produces H2 and metal sulfide (MS) by electrochemical resolution-precipitation. This is very promising because of its low power consumption (0.8 kWh/Nm3-H2) and value-added product MS. This paper provides a state-of-the-art review of the technologies of electrolysis decomposition of H2S. It presents the prospective of hydrogen sulfide conversion from electrochemistry point of view.