The concept of accelerating chemical processes with nanomaterials utilizing the energy collected by plasmon excitations has attracted much interest . Moreover, plasmonic catalysis triggers the segregation of H₂ or adsorbed O₂ (slow processes) under continuous wave excitation via plasmon decay. Here, we present a comprehensive study of the plasmonic and photocatalytic behavior in an environment-friendly medium with AM 1.5G solar light of CuO/Cu2O ultra-thin films grown on a Si substrate using a pulsed laser deposition technique in a vacuum with varying thicknesses. We have produced around 0.59 kmolh⁻¹g⁻¹ H₂ in a CuO/Cu₂O film with a thickness of approximately 27 nm. S-parameter curves from finite element modeling simulations are also used to examine the role of plasmons with metal--dielectric and semiconductor--semiconductor interfaces. The findings demonstrate that the size, composition, and band alignment of two interface materials influence the effects of plasmonic catalysis and synthesis.