Enhanced CO₂ Photoreduction by Ni(OH)_2‐x/WO₃ Nanofibers with Efficient CO₂ Activation and Charge Separation

Abstract Electrospun WO₃ nanofibers show great potential in solar‐powered CO₂ reduction, but they still suffer from rapid charge recombination and difficult CO₂ activation. Here, WO₃ nanofibers are modified by in situ growth of freestanding oxygen‐vacancy Ni(OH)_2‐x nanosheets, and explored their charge separation and CO₂ reduction mechanisms by using in situ characterization techniques and density functional theory (DFT) calculations. Some electrons of Ni(OH)_2‐x transferred to WO₃ nanofibers upon hybridization owing to their remarkable different work function, which induces a built‐in electric field (BIEF) at interfaces with directions pointing from Ni(OH)_2‐x to WO₃. Driven by the electric field, the photogenerated electrons flow to Ni(OH)_2‐x, while the holes remain at WO₃, achieving spatial charge separation. Further, CO₂ adsorbed on Ni(OH)_2‐x shows apparent molecular activation, as suggested by its bent and elongated OCO bonds. The Ni(OH)_2‐x/WO₃ nanofibers exhibit an enhanced CO production rate with respect to WO₃ (54.4 vs 8.1 µmol g⁻¹ h⁻¹). The ¹³CO₂ isotope tracing experiment confirms that the CO product originated from the input CO₂. This work may inspire the development of more advanced photocatalysts for CO₂ activation and photoreduction by defect engineering.