Herein, we report nanosecond, single-pulse laser post-processing (PLPP) in a liquid flat jet with precise control of the applied laser intensity to tune structure, defect sites, and the oxygen evolution reaction (OER) activity of mesostructured Co 3 O 4 . High-resolution X-ray diffraction (XRD), Raman, and Xray photoelectron spectroscopy (XPS) are consistent with the formation of cobalt vacancies at tetrahedral sites and an increase in the lattice parameter of Co 3 O 4 after the laser treatment. X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) further reveal increased disorder in the structure and a slight decrease in the average oxidation state of the cobalt oxide. Molecular dynamics simulation confirms the surface restructuring upon laser post-treatment on Co 3 O 4 . Importantly, the defectinduced PLPP was shown to lower the charge transfer resistance and boost the oxygen evolution activity of Co 3 O 4 . For the optimized sample, a 2-fold increment of current density at 1.7 V vs RHE is obtained and the overpotential at 10 mA/cm 2 decreases remarkably from 405 to 357 mV compared to pristine Co 3 O 4 . Post-mortem characterization reveals that the material retains its activity, morphology, and phase structure after a prolonged stability test.

A comprehensive search for stable structures in the low coverage regime (0-1 ML) and at 2 ML and 3 ML using DFT revealed several new aggregation states of water on the non-polar ZnO(101[combining macron]0) surface. Ladder-like structures consisting of half-dissociated dimers, arranged side-by-side along the polar axis, constitute the most stable aggregate at low coverages (≤1 ML) with a binding energy exceeding that of the monolayer. At coverages beyond the monolayer - a regime that has hardly been studied previously - a novel type of structure with a continuous honeycomb-like 2D network of hydrogen bonds was discovered, where each surface oxygen atom is coordinated by additional H-bonding water molecules. This flat double-monolayer has a relatively high adsorption energy, every zinc and oxygen atom is 4-fold coordinated and every hydrogen atom is engaged in a hydrogen bond. Hence this honeycomb double monolayer offers no H-bond donor or acceptor sites for further growth of the water film. At 3 ML coverage, the interface restructures forming a contact layer of half-dissociated water dimers and a liquid-like overlayer of water attached by hydrogen bonds. The structures and their adsorption energies are analysed to understand the driving forces for aggregation and dissociation of water on the surface. We apply a decomposition scheme based on a Born-Haber cycle, discussing difficulties that may occur in applying such an analysis to the adsorption of dissociated molecules and point out alternatives to circumvent the bias against severely stretched bonds. Water aggregation on the ZnO surface is favoured by direct water-water interactions including H-bonds and dipole-dipole interactions and surface- or adsorption-mediated interactions including enhanced water-surface interactions and reduced relaxations of the water molecules and surface. While dissociation of isolated adsorbed molecules is unfavourable, partial or even full dissociation is preferred for aggregates. Nevertheless, direct water-water interactions change very little in the dissociation reaction. Dissociation is governed by a subtle balance between strongly enhanced water-surface interactions and the large energies required for the geometric changes of the water molecule(s) and the surface. Our conclusions are discussed on the background of the current knowledge on water adsorption at metals and non-metallic surfaces.

Due to the variability of the cation occupancy of octahedral and tetrahedral sites, spinel ferrites and cobaltites are particularly interesting to investigate activity trends in oxidation catalysis. Yet, the preparation of the respective catalyst series remains challenging. We employed pulsed laser defect engineering of CoFe2O4 nanoparticles in water to gradually alter the cation occupancy of octahedral and tetrahedral sites by single laser pulses and study its effect on cinnamyl alcohol oxidation. Three CoFe2O4 catalysts from different synthesis methods resembling different initial site occupancy were chosen as starting materials. The laser‐induced randomization of the cation occupancy was verified by Mössbauer spectroscopy and linearly correlated with the conversion of cinnamyl alcohol while the size and Co : Fe ratio was maintained during laser processing. The study solidifies the importance of octahedral Co3+‐sites and the feasibility of pulsed laser processing for altering the cation occupancy and related crystallographic defect density in oxidation catalysis.

The spinel Co3O4 has many beneficial properties for potential use in catalysis. In operando, water is always present and alters the properties of the catalyst. We have used ab initio molecular dynamics to understand the effect of water and solvation on the structure and reactivity of the Co3O4 (001) A-type and B-type surface terminations. Water adsorbs on both terminations via a partial dissociative mode, and the A-termination is seen to be more reactive. On this surface, a higher degree of dissociation is observed in the topmost layers of the crystal in contact with water. Water dissociates more frequently on the Co2+ sites (about 75%) than on the adjacent Co3+ sites, where the degree of dissociation is about 50%. Increasing water coverage does not change the degree of water dissociation significantly. OH− adsorption on the Co2+ sites leads to a reduction of the amount of reconstruction and relaxation of the surface relative to the clean surface at room temperature. Proton transfer within the water films and between water molecules and surface has localized character. The B-terminated interface is less dynamic, and water forms epitactic layers on top of the Co3+ sites, with a dissociation degree of about 25% in the contact layer.