Electron-rich sulfur sites and dual interfacial bonds in S-scheme heterojunction enable high quantum yield and stable hydrogen production

The intrinsic strong bonding between sulfur sites and adsorbed hydrogen atoms (S-H ads ) in ZnIn 2 S 4 (ZIS) presents a formidable kinetic bottleneck for H 2 desorption. Additionally, low electron mobility and high recombination of charge carrier synergistically limit its photocatalytic H 2 production efficiency. Here, we engineer sulfur vacancies (Sv) to introduce localized defect states near the Fermi level weakens S-H ads bonds by populating S-H antibonding orbitals and shifting the S 3p center, thus overcoming the H 2 desorption barrier. The rapid electron recombination and low electron in Sv-ZIS have been overcome by integrating it with α-MnO 2 into S-scheme heterojunction. The Density-Functional Theory calculations and experimental reveal that interfacial dual bonds of Mn S and Mn In simultaneously lower electron-transfer barriers and stabilize the catalyst structure. The femtosecond transient absorption spectroscopy has demonstrated a ≈ 6-fold enhanced electron lifetime and a drastic reduction in electron recombination. These result in a ≈ 33 times greater H 2 evolution (16.35 mmol g −1 h −1 ) compared with pristine-ZIS having quantum efficiency of 78 % at 420 nm and a long-term stability endorse by only <1 % decay over 6 months. This article therefore marks a step forward advancement in addressing the longstanding chemical and electronic kinetic challenges in ZIS, and may guide developing highly efficient photocatalysts. • An S-scheme heterojunction with dual Mn-S/Mn-In interfacial bonds is constructed, which drastically reduces charge-transfer barriers and stabilizes the catalyst structure, enabling ultrafast electron separation. • Sulfur vacancies create electron-rich S δ- sites that weaken the S-H ads bond by populating its antibonding orbital, effectively overcoming the hydrogen desorption barrier and preventing active site poisoning. • The optimized photocatalyst achieves an exceptional H 2 evolution rate of 16.35 mmol g -1 h -1 and a record-high apparent quantum efficiency of 78% at 420 nm , representing a 33-fold enhancement over pristine ZnIn 2 S 4 . • The catalyst demonstrates outstanding long-term stability , retaining over 96% of its initial activity after 25 hours of cycling and showing less than 1% performance decay after 6 months of ambient storage.