Prof. Dr.-Ing. Stephan Barcikowski
During the second funding period (FP2), C05 advanced pulsed laser defect engineering in liquids (PUDEL) for cobalt spinel (Co3O4) nanoparticles and epitaxial thin-films from consortium partners, establishing isomorphic surface modification with precise control over defect type and density. Studies on pure Co3O4 showed that controlled laser intensity yields defect-rich structures with elevated Co2+ content and conductivity, without CoO by-phases. Co2+ formation was linked to a reductive shift of lattice Co3+ into interstitial positions, distinct from oxygen vacancy formation, as confirmed by electron paramagnetic resonance (EPR) and high-resolution transmission electron microscopy (HR-TEM). These changes enhanced oxygen evolution reaction (OER) activity, though CoO formation reduced the effect. Ultrafast quenching was found to “freeze” metastable phases, with multiple low-energy and single high-energy pulses producing similar catalytic behavior. Thermal liquid-phase alcohol oxidation was unaffected by laser treatment of Co3O4 nanoparticles.
Building on this, C05 developed laser-induced vanadium doping, which suppressed CoO formation, preserved spinel structure, improved OER kinetics, and activated catalysts for both OER and thermal alcohol oxidation reactions. Transferring the method to thin films enabled Fe doping, verified by deep profiling. Higher pulse numbers resulted in deeper penetration and increased alkaline OER activity, as determined by high-resolution SECCM, which provided structure–activity maps linking the enhancements to doping and surface restructuring. In FP3, C05 will extend doping to the anion sublattice (F-, S2-, N3-) to investigate phase transformation kinetics and defect chemistry under operando conditions and expand to radical-mediated mechanisms using radical-mediating agents and fluorescence spectroscopy with tailored fluorophores. Lateral 2D-doping via direct laser interference patterning (DLIP) will produce spatially patterned fluences for simultaneous condition variation, coupled with SECCM for high-throughput screening. These advances will deliver mechanistic insight into active surface dynamics in alcohol oxidation and support the rational design of oxidation catalysts. Serving as a bridge between Areas C, A, and B, C05 will integrate advanced surface science and theory into realistic catalyst performance studies, linking fundamental understanding to application-oriented design.
Figure: SEM image of a Co3O4 thin film on a gold substrate (B10) showing lateral laser-doped spots (C05) (green = 2 PPV, orange = 3 PPV, red = 4 PPV) and untreated reference positions (yellow rectangle), with orientation markers (blue circles). The schematic depicts the lateral PUDEL doping strategy in a millimolar aqueous iron solution, with the PUDEL pulse confined by the laser beam diameter and thermal penetration depth. Electrochemical characterization of the sites was performed using SECCM by A02. [See related publication.]
In the first funding period, the pulsed laser post-processing (PLPP) method was advanced via a novel flat-jet experimental design to gradually increase the defect density in colloidal transition metal oxide nanoparticles and investigate how the defect density affects the respective catalytic activity while the phase purity and BET surface area were maintained. By this single-pulse-per-particle method, the improved alkaline ORR activity of a laser-post processed Co3O4 spinel was correlated to an increased occupancy of Co2+ on tetrahedral defect sites. In the second funding period, the established method and knowledge base for precisely controlling the defect density in colloidal oxide nanoparticles will be expanded by laser-based doping of heteroatoms (Fe, Mn, V) that is required to understand how doped heteroatoms affect the formation or annihilation of active sites.
Due to the complexity of real-structure catalysts, careful control experiments and internal standards are mandatory to identify cross-correlations from different surface terminations. Consequently, the laser-based doping of colloidal real-structure will be complemented by a 2D-material processing scheme, where arrays of laser-induced lateral surface structures are inscribed into thin-film model catalysts that exhibit predetermined crystal facets and are immersed in the aqueous dopant metal cation salt solution during laser processing. This allows differential catalytic studies at laterally doped structure arrays, written with predefined laser intensity and number of laser pulses per spot. This approach automatically delivers internal control at non-irradiated areas, relevant for differential catalytical tests. In combination with advanced surface characterization methods (Area B), specially resolved catalytic testing methods (e.g., SECCM, Area A), and theoretical models this differential model catalysis approach using dopant arrays will allow the identification of active sites and the respective correlation with reaction mechanisms. By also doping colloidal real-structure oxide catalysts in the flat jet setup and the respective investigation of the electrocatalytic (A02) and liquid phase oxidation (A01) catalysis with ensembles as well as single nanoparticles (e.g., in A02) the developed reaction mechanisms will be generalized to bridge the gap between model and real-structure catalysis. Consequently, the project will pave the way for 1) identifying active sites from structure-sensitive spectroscopic methods in Area B as well as theory projects on model catalysts in Area A that are required to 2) understand reaction mechanisms with real-structure catalysts in the respective catalytic systems of Area A.
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Last update: Aug 17, 2026
