Photoelectrochemical CO₂ reduction reaction (PEC-CO₂RR) into multicarbon (C₂ and C₃) products is one of the most favorable paths for converting and utilizing atmospheric CO₂. Although Cu-based photocathodes have unique features that can convert CO₂ into value-added products, they have limited selectivity. In this study, we established the Cu-based heterostructure by introducing 

the Cu₂O (111) phase on the surface of Cu/Cu(OH)₂ nanorods array (CNA) while integrating Pd cocatalyst to improve the selectivity of the C₃ products via PEC-CO₂RR. The acetone is recognized 

as a major C₃ product with a Faradaic efficiency of ∼40 % and a production rate of 323.3 μg/h at a negative applied potential of −0.6 V_RHE. The high selectivity of the CNA/Cu₂O/Pd₂ photocathode is achieved owing to the superior electrochemical active area of 132 μF/cm², electrochemical double layer capacitance of 5.28 mF/cm², and high charge transfer at the electrode/electrolyte interface. Notably, the Pd co-catalyst facilitates supplying an adequate level of ∗CO intermediate at the Cu2O (111) active sites to enable the C–C coupling leading to the formation of multicarbon products with 77% stability retention. During PEC-CO₂RR, the formation of critical intermediates such as ∗CO and ∗COCH₃ are responsible for acetone's selectivity through the hydroxyacetone pathway. Thus, the optimized heterostructure design of the CNA/Cu₂O/Pd photocathodes holding Pd cocatalyst along with the Cu₂O (111) phase is suitable for improving the selectivity of C₃ products via PEC-CO₂RR.