This study investigates the synthesis, characterization, and properties of high-quality dense ZnO (wurtzite) thin films prepared by spray pyrolysis and pulsed reactive magnetron sputtering combined with radio frequency electron cyclotron wave resonance plasma. The films were deposited on four different substrates: FTO, amorphous SiO₂, Si, and Si/SiO₂. The films exhibit a uniform polycrystalline texture with crystallite sizes ranging from 12 to 26 nm, indicating that they consist of 2-10 monolayers of single crystallites. The films show nearly ideal rectifying behavior on an electrochemical interface, with better blocking function observed for spray-pyrolyzed films. The flatband potentials (φb) for ZnO/electrolyte interfaces are approximately 4.3 eV for spray-pyrolyzed films and 4.4 eV for magnetron-sputtered films, with minimal changes due to annealing. Donor concentrations are significantly lower for magnetron-sputtered films compared to spray-pyrolyzed films, attributed to quenching of oxygen vacancies in the ECWR plasma. Work functions for the ZnO/air interface determined by Kelvin probe (φK) are approximately 4.2 eV for all films but systematically larger for annealed films. UV excitation strongly enhances φK by 0.2-0.6 eV, which persists after UV illumination is switched off. Photoelectrochemical water oxidation demonstrates unusually large photocurrents on both spray-pyrolyzed and magnetron-sputtered virgin films, which fade over time, possibly due to photocorrosion and work function changes by oxygen vacancies.This study investigates the synthesis, characterization, and properties of high-quality dense ZnO (wurtzite) thin films prepared by spray pyrolysis and pulsed reactive magnetron sputtering combined with radio frequency electron cyclotron wave resonance plasma. The films were deposited on four different substrates: FTO, amorphous SiO₂, Si, and Si/SiO₂. The films exhibit a uniform polycrystalline texture with crystallite sizes ranging from 12 to 26 nm, indicating that they consist of 2-10 monolayers of single crystallites. The films show nearly ideal rectifying behavior on an electrochemical interface, with better blocking function observed for spray-pyrolyzed films. The flatband potentials (φb) for ZnO/electrolyte interfaces are approximately 4.3 eV for spray-pyrolyzed films and 4.4 eV for magnetron-sputtered films, with minimal changes due to annealing. Donor concentrations are significantly lower for magnetron-sputtered films compared to spray-pyrolyzed films, attributed to quenching of oxygen vacancies in the ECWR plasma. Work functions for the ZnO/air interface determined by Kelvin probe (φK) are approximately 4.2 eV for all films but systematically larger for annealed films. UV excitation strongly enhances φK by 0.2-0.6 eV, which persists after UV illumination is switched off. Photoelectrochemical water oxidation demonstrates unusually large photocurrents on both spray-pyrolyzed and magnetron-sputtered virgin films, which fade over time, possibly due to photocorrosion and work function changes by oxygen vacancies.