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 ZnIn₂S₄ (ZIS) presents a formidable kinetic bottleneck for H₂ desorption. Additionally, low electron mobility and high recombination of charge carrier synergistically limit its photocatalytic H₂ 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 H₂ desorption barrier. The rapid electron recombination and low electron in Sv-ZIS have been overcome by integrating it with α-MnO₂ 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 H₂ 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.