A Z‐Scheme Heterojunctional Photocatalyst Engineered with Spatially Separated Dual Redox Sites for Selective CO₂ Reduction with Water: Insight by In Situ µs‐Transient Absorption Spectra

Abstract Solar‐driven CO₂ reduction by water with a Z‐scheme heterojunction affords an avenue to access energy storage and to alleviate greenhouse gas (GHG) emissions, yet the separation of charge carriers and the integrative regulation of water oxidation and CO₂ activation sites remain challenging. Here, a BiVO₄/g‐C₃N₄ (BVO/CN) Z‐scheme heterojunction as such a prototype is constructed by spatially separated dual sites with CoO_x clusters and imidazolium ionic liquids (IL) toward CO₂ photoreduction. The optimized CoO_x‐BVO/CN‐IL delivers an ≈80‐fold CO production rate without H₂ evolution compared with urea‐C₃N₄ counterpart, together with nearly stoichiometric O₂ gas produced. Experimental results and DFT calculations unveil the cascade Z‐scheme charge transfer and subsequently the prominent redox co‐catalysis by CoO_x and IL for holes‐H₂O oxidation and electrons‐CO₂ reduction, respectively. Moreover, in situ µs‐transient absorption spectra clearly show the function of each cocatalyst and quantitatively reveal that the resulting CoO_x‐BVO/CN‐IL reaches up to the electron transfer efficiency of 36.4% for CO₂ reduction, far beyond those for BVO/CN (4.0%) and urea‐CN (0.8%), underlining an exceptional synergy of dual reaction sites engineering. This work provides deep insights and guidelines for the rational design of highly efficient Z‐scheme heterojunctions with precise redox catalytic sites toward solar fuel production.