To help expedite the design of new alloy catalysts for energy-related applications, it is critical to understand the chemical ordering of the catalyst and the adsorbate coverage under operating conditions. Using the hydrogen evolution reaction (HER) as the model reaction, we showcase how first-principles calculations coupled with the cluster expansion method (CE) [1], may be used to (I) elucidate stable configurations of bimetallic nanoalloy catalysts and (II) predict the equilibrium configurations of adsorbates on Pt catalyst surface.For case (I), we conduct a comprehensive groundstate search for stable nanoalloy configurations for ~1 nm sized Pd-Pt [2] nanoalloy across all possible compositions. The groundstate configurations exhibit Pt(core)-Pd(shell) structures in general, agreeing with experimental observations. We further show that the 1 nm Pt nanoparticle is not expected to be a good HER catalyst as it adsorbs hydrogen (H) atoms either too strongly or weakly on its facets. However, addition of Pd appropriately tunes the H adsorption energy to achieve an optimal nanoalloy catalyst.For case (II), we predict the coverage of adsorbed hydrogen on Pt (111) surface, taking into consideration fcc, atop and hcp adsorption sites simultaneously. Via the predicted adsorption isotherm versus standard hydrogen potential (U = 0), we show that traces of H*atop and H*hcp are expected even at underpotential condition and these minority species are believed to be kinetically active in the HER.[1] Sanchez, J.M., Ducastelle, F., and Gratias, D., Physica 128A, 334 (1984)[2] Tan, T.L., Wang, L.-L., Johnson, D.D., and Bai, K., Nano Lett12, 4875 (2012).[3] Tan, T.L., Wang, L.-L., Johnson, D.D., and Bai, K., J. Phys. Chem. C, accepted (2013).

Use of first-principles cluster expansion method for designing materials in energy research

247th National Meeting (2014)

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