Dr. Harol Moreno Fernández, in collaboration with Dr. Mohammad Amirabbasi from the FG Material Modeling at TU Darmstadt, and in close collaboration with Crizaldo Mempin, Jr. from the Dutch Institute for Fundamental Energy Research, Dr. Garlef Wartner and Dr. Marc F. Tesch from the Max Planck Institute for Chemical Energy Conversion, and Dr. Esmaeil Adabifiroozjaei and Prof. Leopoldo Molina-Luna from the Advanced Electron Microscopy Division at TU Darmstadt, report how plasma-assisted synthesis can be used to tailor hydroxyl defects, Ni vacancies, and oxygen-hole states in NiO thin films relevant to the oxygen evolution reaction. Combining DFT+U with advanced spectroscopy and electrochemical analysis, the study shows that oxygen-rich plasma conditions stabilize vacancy-related ligand-hole states and enhance Ni–O covalency, whereas H2O incorporation promotes local hydroxylation, modifies near-valence-band states, and facilitates transformation toward the OER-active NiOOH phase. These findings establish a plasma-controlled strategy to predefine defect configurations and catalytic functionality in Ni-based oxide thin films.