Surface Energy as a Descriptor of Catalytic Activity

Abstract

Computational searches for catalysts of the hydrogen evolution reaction commonly use the hydrogen binding energy (HBE) as a predictor of catalytic activity. Accurate evaluation of the HBE, however, can involve large periodic supercell slab models that render high-throughput screening relatively expensive. In contrast, calculations of other relevant surface properties, such as the surface energy, work function, and potential of zero charge (PZC), require only small surface unit cells and are hence less expensive to compute. Correlations between catalytic activity and these surface properties warrant exploration because of this reduced computational cost. Here, we use density functional theory in conjunction with three different exchange-correlation functionalsthe local density approximation (LDA), the Perdew−Burke− Ernzerhof (PBE) generalized gradient approximation, and the PBEsol functional (a reparameterization of the PBE functional)to calculate the lattice constants, surface energy, cohesive energy, and work function of six common catalysts: three metals (Au, Pd, and Pt) and three transitionmetal carbides (TMCs; WC, W 2 C, and Mo 2 C). The three exchange-correlation functionals produce identical trends, and PBEsol yields results between those calculated using LDA and PBE and most often closer to experiment. We therefore use PBEsol to obtain the surface energy, work function, and PZC of nine novel hybrid catalysts, each containing a metal monolayer on a TMC substrate. Importantly, a volcano-shaped correlation between the experimental exchange current density and the theoretical surface energies emerges. We also investigate solvation effects on the surface energy and work function using a polarizable continuum model within the framework of joint density functional theory. For these particular materials, the surface energies in vacuum are nearly unchanged upon exposure to an aqueous solution, prior to any reaction with water. The volcano-shaped correlation observed between the exchange current densities and the surface energies is not observed for the work function or PZC. Our work thus reveals opportunities for more rapid computational screening of reduced Pt-loading catalysts using the surface energy as a computationally efficient catalytic descriptor.

Stable Active Sites on Ni12P5 Surfaces for the Hydrogen Evolution Reaction

“…[28] However, Zhuang et al found that activity and stability do not always obey this relationship, and surface stability that is too high or too low corresponds to poor HER activities for metal or transition metal carbides. [29] Recent experimental results also verify that balancing of the activity and stability is possible for nanoporous core-shell iridium/iridium oxide for oxygen evolution catalysts. [30] The results of the present study indicate that bridge Ni 2 Ni 3 of the (111)C is the most active (ΔG H* ¼ 0) and unstable (6 coordination number).…”

“…Danilovic et al also indicate that the degree of activity is inversely proportional to the stability . However, Zhuang et al found that activity and stability do not always obey this relationship, and surface stability that is too high or too low corresponds to poor HER activities for metal or transition metal carbides . Recent experimental results also verify that balancing of the activity and stability is possible for nanoporous core‐shell iridium/iridium oxide for oxygen evolution catalysts .…”

“…To date, the relationship between activity and stability has not been fully revealed. Some reported works showed that activity and stability are incompatible, whereas other works reported that it is possible to balance the activity and stability …”

“…Some reported works showed that activity and stability are incompatible, [16] whereas other works reported that it is possible to balance the activity and stability. [17] This investigation reports a comprehensive analysis of the active sites and stability of different surface orientations and terminations of Ni 12 P 5 using density functional theory (DFT) calculations. The current study also provides a mechanism of the HER activity and stability, and then predicts the sites with both high activity and stability.…”

Adsorption Energetics of Atoms and Diatomic Gases with Electrocatalysis Approach towards Hydrogen and Oxygen Evolution Reaction on Pt Surfaces

“…Significant experimental and DFT studies have been carried out to demonstrate the both polycrystalline, and well‐defined closed pack platinum surfaces revealing the fact that the HER activity varies with the site and geometrical orientations . Due to its high price and a shortage of Pt; many efforts via nanosizing, and alloying have been taken place to make it more suitable for commercial applications in recent years …”