Reverse quantum wells in gradient-doped CdS for photocatalytic H₂O₂ production

The photocatalytic O₂ reduction to produce H₂O₂ offers significant environmental benefits. However, its efficiency is hindered by rapid charge recombination and sluggish catalytic kinetics in the catalyst. Traditional elemental doping has been employed to mitigate these issues, but its efficacy is limited as heteroatoms within the bulk often trap charge carriers. To address these challenges, we propose a gradient doping strategy. Unlike uniform doping, gradient doping introduces additional active sites on the catalyst surface. Our engineered gradient Mn-doped CdS photocatalyst demonstrated a remarkable H₂O₂ generation rate of 1874 μmol g⁻¹ h⁻¹, with an apparent quantum efficiency of 65.2% at 475 nm. The gradient distribution of Mn creates reverse quantum wells within the CdS matrix, which significantly enhances charge extraction from the bulk to the surface. The surface enrichment of Mn not only facilitates the adsorption and activation of O₂ but also promotes the formation of the crucial *OOH intermediate, thereby accelerating H₂O₂ production.