Hydrogen Sulfide Splitting into Hydrogen and Sulfur through Off-Field Electrocatalysis

Hydrogen sulfide (H₂S), a toxic gas abundant in natural gas fields and refineries, is currently being removed mainly via the Claus process. However, the emission of sulfur-containing pollutants is hard to be prevented and the hydrogen element is combined to water. Herein, we report an electron-mediated off-field electrocatalysis approach (OFEC) for complete splitting of H₂S into H₂ and S under ambient conditions. Fe­(III)/Fe­(II) and V­(II)/V­(III) redox mediators are used to fulfill the cycles for H₂S oxidation and H₂ production, respectively. Fe­(III) effectively removes H₂S with almost 100% conversion during its oxidation process. The H⁺ ions are reduced by V­(II) on a nonprecious metal catalyst, tungsten carbide. The mediators are regenerated in an electrolyzer at a cell voltage of 1.05 V, close to the theoretical potential difference (1.02 V) between Fe­(III)/Fe­(II) and V­(II)/V­(III). In a laboratory bench-scale plant, the energy consumption for the production of H₂ from H₂S is estimated to be 2.8 kWh Nm^–3 H₂ using Fe­(III)/Fe­(II) and V­(II)/V­(III) mediators and further reduced to about 0.5 kWh Nm^–3 H₂ when employing well-designed heteropolyacid/quinone mediators. OFEC presents a cost-effective approach for the simultaneous production of H₂ and elemental sulfur from H₂S, along with the complete removal of H₂S from industrial processes. It also provides a practical platform for electrochemical reactions involving solid precipitation and organic synthesis.