CuO nanoparticles with diameter in the 20-30 nm range were prepared by a spinning disk reactor at the rate of 16.9 kg/day based on the process intensification concept. The intense environment, that is, vigorous mixing and fast reaction at the same time, created within an initially crystal-free liquid film moving over the disk, generated very high supersaturation, and consequently small and fairly uniform crystals were formed via precipitation. These CuO nanoparticles were spin coated and sintered at 450 degrees C for 1 h to form a thin film electrode for use in a photoelectrochemical cell. The cell had a 1.20% solar to hydrogen conversion efficiency which is the highest among intrinsic CuO photoelectrochemical (PEC) cells reported to date in the literature. The bandgap of CuO films sintered at 450 degrees C for 1 h was 1.68 eV. The charge carrier density was 9.0 X 10(20) cm(-3) and the conduction and valence band edges were located at -3.54 and -5.22 eV, respectively. Furthermore, a detailed comparison based on the preparation method, particle size, bandgap, porosity, and conductivity of the films in the CuO PEC cell literature is also reported in this study.