(415f) More Accurate Depiction of Adsorption Energy on Transition Metals Using Work Function As One Additional Descriptor

Authors: 
Shen, X., University of Akron
Peng, Z., The University of Akron
Liu, B., Kansas State University
Pan, Y., University of Akron
Transition metals (TMs), benefiting from their active interactions with chemical species owing to partial occupancy of the d bands, represent one most important category of catalysts and have been widely used in many reactions. The catalytic properties of TMs in a chemical reaction are primarily determined by adsorption energy (Eads) of the involved species. In this regard, it is of high research significance to get accurate Eads values, however, which is often challenging be measured experimentally. Active research interests have been devoted to determine Eads by establishing an exact relationship with measurable catalyst parameters like the d-band (εd) theory, which was based on the Newns-Anderson model and suggested for use by Hammer and Nørskov. It describes a simple Eads–εd linear correlation and has been widely adopted for application, which turns out to work well for certain adsorption systems, for instance H2 and CO adsorption, but becomes less effective for many other systems, such as O, OH and OOH adsorption. These controversial results suggest the current Eads–εdlinear correlation could be oversimplified to describe these adsorption systems and εd might not be the only influencing parameter, thus improvements are needed.

Considering the fact that band hybridization and electron transfer could occur simultaneously when a molecule adsorbs to a TM surface, we propound that Eads contains a mixture of covalent and ionic contributions (i.e., Eads=Ecovalent + Eionic). The Ecovalent term would be describable using the εd parameter as it accounts for the band hybridization, whereas the Eionic term is determined by the charge transfer between TM and adsorbing molecules and thus would be related to the work function (W) parameter. Herein by taking both the ionic and covalent contributions into account, we suggest a new description model for Eads by dividing it into Ecovalent and Eionic components and adding W as one additional descriptor. We study the adsorption of O, OH, and OOH groups on TM surfaces using the new Eads–(εd, W) model with the explicit formula as Eads = f(εd, W) = z0+ a × εd + k ×(W - W0)2 and achieve significantly better goodness of fit compared to the current Eads–εd model. We further demonstrate the new Eads–(εd, W) model can better predict activity property of TMs in oxygen reduction reaction (ORR) benefiting from a more accurate description of the oxygen binding energy (EO).

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