Influence of coverage dependence on the thermophysical properties of adsorbates and its impact on microkinetic models

This work focuses on the impact of lateral interactions on the thermophysical properties of adsorbates. We present different parameterizations for coverage-dependent enthalpy, entropy, and heat capacity in a mean-field microkinetic model. These models are tested against two systems, CO/Pt(111) and CO/Co(0001), using two different funtionals. A detailed investigation into how coverage influences the thermophysical properties of \co{} is presented. Our analysis of the repulsive interaction in adsorption energy suggests that coverage effects are mainly indirect (adsorbate--metal and surface relaxation) for lower coverages, but are both indirect and direct (adsorbate--adsorbate) for higher coverages. We place a particular emphasis of studying the impact of coverage on the vibrational partition function and how this affects the entropy of adsorbates. Higher coverages typically lead to increased repulsive interactions, which should further constrain the large-amplitude modes that contribute the most to the vibrational entropy. In some cases, however, the opposite effect occurred; the vibrational entropy actually increased, because surface crowding forced adsorbates to different binding locations that had lower frequencies. However, our result highlighted cases where coverage-dependent entropy should be included, such as for adsorbates with lateral vibrational modes and for systems at high temperatures. These methods for including coverage-dependent properties into mean-field microkinetics in a thermodynamically consistent way are now available in the open-source software Cantera.