Fe─S Bond-Mediated Efficient Electron Transfer in Quantum Dots/Metal-Organic Frameworks for Boosting Photoelectrocatalytic Nitrogen Fixation

Effective electron supply to produce ammonia in photoelectrochemical nitrogen reduction reaction (PEC NRR) remains challenging due to the sluggish multiple proton-coupled electron transfer and unfavorable carrier recombination. Herein, InP quantum dots decorated with sulfur ligands (InP QDs-S²⁻) bound to MIL-100(Fe) as a benchmark catalyst for PEC NRR is reported. It is found that MIL-100(Fe) can combined with InP QDs-S²⁻ via Fe─S bonds as bridge to facilitate the electron transfer by experimental results. The formation of Fe─S bonds can facilitate electron transfer from inorganic S²⁻ ligands of InP QDs to the Fe metal sites of MIL-100(Fe) within 52 ps, ensuring a more efficient electron transfer and electron-hole separation confirmed by the time-resolved spectroscopy. More importantly, the process of photo-induced carrier transfer can be traced by in situ attenuated total reflection surface-enhanced infrared tests, certifying that the effective electron transfer can promote N≡N dissociation and N₂ hydrogenation. As a result, InP QDs-S²⁻/MIL-100(Fe) exhibits prominent performance with an outstanding NH₃ yield of 0.58 µmol cm⁻² h⁻¹ (3.09 times higher than that of MIL-100(Fe)). This work reveals an important ultrafast dynamic mechanism for PEC NRR in QDs modified metal-organic frameworks, providing a new guideline for the rational design of efficient MOFs photocathodes.