The mechanism of hierarchical regulation to improve stability of heavy-metal-free Zn:CuFeS₂ quantum dots sensitized solar PEC cells for highly-efficient hydrogen evolution

The photo-corrosion of sulfide quantum dots (QDs) always limits the applications in photoelectrochemical (PEC) cells as photo-sensitizers. Herein, Zn-doped CuFeS₂ (ZCIS) QDs were synthesized to sensitize TiO₂/F-doped tin oxide (FTO) glass photoanode. After Zn introduction, the highly chemically active S₂²⁻ in CuFeS₂ (CIS) QDs disappears, and the average grain size of Zn:CuFeS₂ reduces, enhancing the quantum confinement effect that accelerates the separation and transfer of photogenerated carriers. After coated with ZnS passivation layer, ZnS/ZCIS/TiO₂/FTO photoanode was employed for H₂ evolution together with a Pt sheet electrode in aqueous electrolyte. The I-type ZnS/ZCIS heterojunction not only suppresses back electron transfer, but also promotes transfer of carriers furtherly. Zn doping and ZnS coating inhibit photo-corrosion of ZCIS QDs, and improve PEC performance and stability significantly. Under one sun illumination (100 mW/cm²), ZnS/ZCIS/TiO₂/FTO photoanode based cell has achieved accumulative H₂ yield of 642.17 μmol/cm² for 4 h with average rate of 160.54 μmol/(cm²·h) at 0.6 V bias. After 16-h H₂ evolution in 4-cycle test, the average rate decreases by only 2.13%.