Plasma engineered Hydroxyl Defects in NiO a DFTSupported-Spectroscopic Analysis of Oxygen Hole States and Implications for Water Oxidation

TL;DR

This study combines DFT calculations and plasma synthesis to control defect chemistry in NiO, revealing how plasma conditions influence oxygen vacancies, hydroxylation, and electronic structure to enhance water oxidation catalysis.

Contribution

It introduces a plasma-assisted method to precisely tune defect landscapes in NiO, impacting its catalytic activity for water oxidation.

Findings

Oxygen-rich plasmas create Ni vacancies that stabilize oxygen hole states.

H2O during growth induces hydroxylation, restoring Ni2+ coordination.

Hydroxylation preserves the lattice while modifying local electronic states.

Abstract

Controlling lattice oxygen reactivity in earth abundant OER catalysts requires precise tuning of defect chemistry in the oxide lattice. Here, we combine DFT+U calculations with plasma assisted synthesis to show how O2 and H2O in the discharge govern vacancy formation, electronic structure, and catalytic predisposition in NiO thin films. Oxygen rich plasmas generate isolated and clustered Ni vacancies that stabilize oxygen ligand hole states and produce shallow O 2p Ni 3d hybrid levels, enhancing Ni O covalency. In contrast, introducing H2O during growth drives local hydroxylation that compensates vacancy induced Ni3+ centers, restoring Ni2+ like coordination, suppressing deep divacancy derived in gap states, and introducing shallow Ni O H derived valence-band tails. EXAFS confirms that hydroxylation perturbs only the local environment while preserving the medium-range NiO lattice, and Ni L-edge spectroscopy shows a persistent but redistributed ligand-hole population. These complementary vacancy and hydroxylation driven pathways provide a plasma controlled route to pre define electronic defect landscapes in NiO and to tune its activation toward OER relevant NiOOH formation.