S-scheme Co${}_9$S${}_8$@Cd${}_{0.8}$Zn${}_{0.2}$S-DETA hierarchical nanocages bearing organic CO${}_2$ activators for photocatalytic syngas production

Delicate modulations of CO${}_2$ activation and charge carrier separation/migration are challenging, yet imperative to augment CO${}_2$ photoreduction efficiency. Herein, by supporting diethylenetriamine (DETA)-functionalized Cd${}_{0.8}$Zn${}_{0.2}$S nanowires on the exterior surface of hollow Co${}_9$S${}_8$ polyhedrons, hierarchical Co${}_9$S${}_8$@Cd${}_{0.8}$Zn${}_{0.2}$S-DETA nanocages are fabricated as an S-scheme photocatalyst for reducing CO${}_2$ and protons to produce syngas (CO and H${}_2$). The amine groups strengthen adsorption and activation of CO${}_2$, while the 'nanowire-on-nanocage' hierarchical hollow heterostructure with an S-scheme interface boosts separation and transfer of photoinduced charges. Employing Co(bpy)${}_3$${}^{2+}$ as a cocatalyst, the optimal photocatalyst effectively produces CO and H${}_2$ 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 CO${}_2$-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 CO${}_2$ reduction mechanism is proposed. (© 2023 Wiley‐VCH GmbH)