coadsorbaten

Coadsorbaten, in English more commonly referred to as coadsorbates, are species that adsorb onto a surface together with another adsorbed species. They are a central concept in surface science, catalysis, and electrochemistry, where multiple species occupy a surface at the same time and influence each other’s adsorption behavior, coverage, and the progression of surface reactions.

Coadsorption can occur through several mechanisms. In competitive coadsorption, adsorbates compete for the same adsorption sites, altering surface coverages and reaction rates. In cooperative or associative coadsorption, one adsorbate stabilizes another via attractive interactions, electronic effects, or surface reconstruction, potentially changing adsorption energies and the geometry of the adsorbed layer. Lateral interactions, steric constraints, and charge transfer between coadsorbates and the substrate contribute to the overall effect on the surface.

Thermodynamic modeling of coadsorption often extends classical isotherms to include interactions between adsorbates. Models such as the Frumkin or lattice-gas approaches, and competitive Langmuir-type formulations, are used to describe how coverages depend on temperature, pressure, or electrochemical potential. Experimental data from spectroscopy, microscopy, and electrochemical measurements are integrated with these models to understand adsorption equilibria and kinetic barriers.

Significance extends to catalysis and electrochemistry. Coadsorbed species can block or modify active sites, alter reaction pathways, and change surface properties such as work function and potential. Understanding coadsorption helps explain catalytic selectivity, poisoning effects, and the design of surfaces with tailored reactivity. Common study systems involve CO, hydrogen, oxygen, water, and halides on transition metal or oxide surfaces, examined with in situ techniques to capture real-time interactions.