Mechanistic Understanding of Laser‐Induced Defect Engineering of Anisotropic Cobalt Oxide Spinel Platelets in Water

In this study, we employ the pulsed laser defect engineering in liquid (PUDEL) to tailor the surface properties of cobalt (II, III) oxide (Co 3 O 4 ) platelets grown in the < 111 > direction. By varying the laser intensity and pulse number, we systematically investigate the relationship between defect formation and catalytic performance in the oxygen evolution reaction (OER) and selective oxidation of two alcohols. Our results reveal that the PUDEL processing leads to the formation of lattice distortions, the gradual alteration of three different paramagnetic defect sites, a partial reduction of Co 3 O 4 , and enrichment of the Co 3 O 4 (111) surface with hydroxyl groups (*OH), which significantly enhances OER activity. Theoretical investigations confirm that optimized hydroxyl coverage is critical for determining OER activity. The observed trends in selectivity and conversion efficiency for the selective oxidation of cinnamyl alcohol (CA) and ethylene glycol (EG) suggest different reaction mechanisms. The activity trend of the selective oxidation of CA appears to follow the trend of a defect‐attributed paramagnetic species that was assigned to a surface‐near, distorted high‐spin (S = 3/2) Co 2+ . In turn, the catalytic activity and OER activity trends for the EG oxidation showed similar trends, which followed the density of a paramagnetic CoO x species observed during EPR spectroscopy. In particular, the highest OER activity and EG conversion were both found for moderate (2 PPV, ), yet not too intense PUDEL processing. Our findings establish PUDEL as a precise method for catalyst optimization, both for thermal and electro‐catalytic oxidation over defect‐enriched cobalt oxides, which enables the correlation of specific laser‐induced defects with catalytic activity trends.