Experimental and Theoretical Exploration of In Situ Grown Fe₃S₄/Co₃S₄ Heterostructure as Efficient Catalyst for I₃ ⁻ Reduction Reaction

Evolving low-cost transition metal sulfides heterostructures using simple yet high-efficiency synthesis methods to be grown directly on fluorine-doped tin oxide glass (FTO) as a counter electrode (CE) is an immense challenge for dye-sensitized solar cells (DSSCs). Herein, Fe3S4/Co3S4 heterostructures with urchin-like structures were uniformly deposited on FTO substrates by a two-step hydrothermal reaction. DSSC constructed with the Fe3S4/Co3S4 CE achieves high power conversion efficiency (8.43%), which is better than the pure Pt CE (7.60%) measured under the same circumstances. The high performance comes down to the fact that Fe3S4/Co3S4 grows directly on the surface of FTO and achieves the uniform film thickness, which is conducive to the full contact of the electrolyte and accelerates the charge transfer. Moreover, density functional theory (DFT) indicates that the charge density changes at the interface of Fe3S4/Co3S4 enhance the interaction between Fe 3d orbitals and I 5p orbitals, thereby the synergistic effect between Fe3S4 and Co3S4 achieving outstanding catalytic performance for I ions. This work paves the way for direct growth of heterostructure materials on substrates as electrodes avoiding subsequent complex processing for energy-related fields.