S‐Scheme Co₉S₈@Cd_0.8Zn_0.2S‐DETA Hierarchical Nanocages Bearing Organic CO₂ Activators for Photocatalytic Syngas Production

Abstract Delicate modulations of CO₂ activation and charge carrier separation/migration are challenging, yet imperative to augment CO₂ photoreduction efficiency. Herein, by supporting diethylenetriamine (DETA)‐functionalized Cd_0.8Zn_0.2S nanowires on the exterior surface of hollow Co₉S₈ polyhedrons, hierarchical Co₉S₈@Cd_0.8Zn_0.2S‐DETA nanocages are fabricated as an S‐scheme photocatalyst for reducing CO₂ and protons to produce syngas (CO and H₂). The amine groups strengthen adsorption and activation of CO₂, while the “nanowire‐on‐nanocage” hierarchical hollow heterostructure with an S‐scheme interface boosts separation and transfer of photoinduced charges. Employing Co(bpy)₃²⁺ as a cocatalyst, the optimal photocatalyst effectively produces CO and H₂ in rates of 70.6 and 18.6 µmol h⁻¹ (i.e., 4673 and 1240 µmol g⁻¹ h⁻¹), respectively, affording an apparent quantum efficiency of 9.45% at 420 nm, which is the highest value under comparable conditions. Ultraviolet photoelectron spectroscopy, Kelvin probe, and electron spin resonance confirm the S‐schematic charge‐transfer process in the photocatalyst. The key COOH^* species responsible for CO₂‐to‐CO reduction is detected by in‐situ diffuse reflectance infrared Fourier transform spectroscopy and endorsed by density functional theory calculations, and thus a possible CO₂ reduction mechanism is proposed.