Electrode-engineered photocatalytic fuel cell: synergistic effect of sulfide oxidation and oxygen reduction driven sulfide wastewater treatment and valorization

Photocatalytic fuel cell (PFC) provides a promising method for environmental remediation and energy recovery. However, how to efficiently generate, extract, and utilized charge carriers is a crucial concern for PFC. A CdS@ZnO/ITO photoanode was well-designed for sulfide (S 2− ) oxidation reaction (SOR) and a nitrogen-doped graphite felt (GF-N) cathode was designed for oxygen reduction reaction (ORR). The CdS@ZnO/ITO had a layered structure where ZnO nanosheets were inserted between CdS and ITO, forming a stepwise energy level alignment at the CdS/ZnO interface. At the junction of CdS and ZnO, a robust internal electric field modulated Type-II heterojunction with an interfacial O-Zn-S bond acted as a charge transfer bridge, promoting the extraction and quick transfer of photogenerated electrons. On the other hand, GF-N possesses a pore structure and abundant N-active sites, favoring the catalysis toward the two-electron route of ORR. Benefiting from the clever design of the electrodes, a PFC system through SOR coupled with ORR was used for the purification of S 2− -rich wastewater. In the PFC, 89.0 % sulfur recovery, 10.8 mmol/L H 2 O 2 yield, and 23.0 W/m 2 P max were simultaneously achieved under simulated sunlight (light intensity: 100 mW/cm 2 ) for 4 h at an initial S 2− concentration of 500 mg/L. Furthermore, the novel PFC system exhibits a good potential for the purifying of shale gas and leather wastewater.