One-Step Molten Salt Constructing Double S-Scheme K_0.2WO₃/NiO/NiWO₄ Heterojunction for Photocatalytic CO₂ Reduction

Rapid charge separation and transfer is the key scientific problem in photocatalysis. The construction of S-scheme heterojunction is one of the effective strategies to promote charge separation and maintain the strong redox properties. Herein, the NiO, K_0.2WO₃, and NiWO₄ ternary double S-scheme K_0.2WO₃/NiO/NiWO₄ heterojunction (W/NiO) was created by a one-step molten salt method. Ultraviolet-visible (UV-Vis) diffuse reflectance spectra, photoluminescence (PL) spectra, photoelectrochemistry tests, and other analyses revealed that the double S-scheme heterostructure broadened the spectral response range of NiO and promoted its separation of photocarriers. Compared with pristine NiO, the modified double S-scheme heterojunction enhanced the surface adsorption of water molecules and the accumulation of intermediate product of HCOO^-, and optimized the CO₂ reduction system, realizing the improved CO yield of 373 μmol·g^-1·h^-1 in Ru(byp)₃²⁺/ethanolamine of CO₂ reduction system. This study indicates that double S-scheme heterojunction could facilitate efficient photogenerated charge transfer and separation, thereby achieving high activity and selectivity for CO₂ photoreduction. Our work provides a reference for the one-step construction of double S-scheme heterojunction.