<p>Photocatalytic CO₂ reduction for solar fuel production is a critical technology enabling carbon cycling and efficient renewable energy storage. However, conversion efficiency remains severely limited by bottlenecks such as rapid recombination of photogenerated charge carriers, high activation barriers for CO₂ molecules, and inadequate catalyst stability. To overcome these challenges, this study constructed an <i>in situ</i> ZrO₂ nanoparticle protective layer on CdS nanospheres, yielding a ZrO₂/CdS-20 (ZOCS-20) core-shell composite photocatalyst. Under light conditions, this catalyst demonstrated exceptional performance, with a CO production rate of 330.23 µmol/(g·h) and near 100% CO selectivity. Systematic characterization and density functional theory (DFT) calculations reveal the underlying enhancement mechanism. The core-shell heterostructure suppresses charge recombination through interfacial engineering, significantly improving charge separation efficiency and carrier transport kinetics while enhancing material stability. Crucially, strong electron coupling at the ZrO₂/CdS interface shifts the d-band center of catalyst toward the Fermi level, strengthening CO₂ chemisorption and lowering its activation barrier. The optimized electronic interface also reduces the energy barrier for forming the *COOH intermediate, substantially decreasing activation energy of the rate-determining step (RDS) and providing additional thermodynamic driving force. This work elucidates an interface-band synergy enhancement mechanism, offering both theoretical insights and experimental guidance for the design of efficient photocatalytic materials.</p>