Several catalytic reactions take place at liquid-metal interfaces. Water is often present at a metal catalyst surface either as a reactant, solvent, or product. Depending upon the catalytic and experimental conditions, the presence of water at the metal surface can increase or decrease reaction rates, such as in electrochemical reactions, CO oxidation or Fischer-Tropsch reactions. Understanding the role of water at the water-metal interfaces is thus of prime importance. Quantum mechanical modeling tools such as density functional theory (DFT) can provide useful atomic level insights at the water-metal interfaces and the role water plays in catalytic reactions. Because of the complexity of modeling water at the water-metal interfaces, often in DFT calculations the solvent environment is approximated by vacuum, which may lead to false conclusions. Thus, modeling of water at heterogeneous interfaces is crucial for a realistic description of catalytic reactions.<br/> <br/>Water can be modeled within the DFT framework using explicit (both water and reaction system are treated using DFT), implicit (thermodynamically averaged description of solvent through a continuum model), and hybrid (combination of explicit and implicit) solvation methods. Implicit solvation is a computationally cheap solvent model that has advances in DFT codes used by the heterogeneous catalysis community. However, a detailed assessment of this method is lacking. We studied different implicit solvent models in common DFT codes on a Pt(111) surface. Our adsorption studies of several different kinds of adsorbates showed that the presence of water can change adsorption energies by up to 0.44 eV compared to vacuum results. These results can be explained by analyzing chemical descriptors, such as dipole moments and the adsorbate charge. Further, we looked at four different aqueous phase reactions on Pt(111) surface in the presence of water. The reaction energies were affected by a magnitude of up to 0.23 eV compared to vacuum. We found that species which are capable of strong hydrogen bonding may not be properly accounted for by implicit solvation. Our results show when implicit solvation is accurate and when caution must be exercised. Our work provides insights into a better modeling of catalytic reactions at metal-water interfaces.<br/> <br/>

Assessing implicit solvation models for describing surface chemistry at aqueous/Pt(111) interfaces

254th National Meeting (2017)

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