Computational Search for a Descriptor of Electrocatalysis in Transition Metal-Oxides
Authors: Bothra Neha , Bajdich Michal , Comer Benjamin , Winther Kirsten , Pedersen Frank Abild 
Published: September 2023

Currently, the most effective electrocatalysts for oxygen reduction (ORR) and oxygen evolution reactions (OER) are comprised of noble metal oxides, which bring issues of high cost and scarcity. Discovering earth-abundant alternatives is challenging due to the costly and time-consuming experiments. High-throughput atomistic simulation of catalysts can be an efficient route for enabling the better design and discovery of new electrocatalysts. The efficient use of this approach relies on an activity descriptor that can capture the qualitative and quantitative catalytic trends. In the past, multiple descriptors based on electronic properties have been proposed either reaction-specific or system specific. Therefore, we need a descriptor, which can capture the bonding strength accurately for any sort of reaction or system.
In this work, we study the trends of O*/OH* adsorption energies for a wide range of pure metal oxide polymorphs[1] namely rocksalt (MO), corundum (M2O3), rutile (MO2), pentoxide (M2O5) and MO3 in all conceivable oxidation states i.e., +2, +3, +4, +5 and +6 respectively. The main drivers of the adsorption energy are the extent of filling of the bonding and anti-bonding orbitals, along with the spin-dependent coupling strength between the metal-d and oxygen-2p atomic orbitals. This property can be easily captured with the help of crystal orbital Hamiltonian population (COHP). We have observed a strong correlation between the integrated COHP I(COHP) of the bulk system and the adsorption energy, which indicates expensive surface-level electronic calculations can be replaced by bulk-level computations. However, this correlation does not hold on two classes of systems: (i) d0 systems and (ii) systems with significant surface distortion during the reaction. We have considered a different approach to address these systems, where instead of a single bond ICOHP, we account for the summation of the ICOHP around the active site.
In search of promising catalysts, we also report tetrahedral systems for 3d, 4d and 5d transition metal oxides, i.e., zinc blende, wurtzite and square planar systems. This will broaden the horizon of possible catalysts along the octahedral systems. We correlate the bulk ICOHP with the surface reactivity of these systems, which highlights the applicability of ICOHP as a universal descriptor across a series of metal oxide systems and guide the design of novel catalysts.
This research was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Catalysis Science Program to the SUNCAT Center for Interface Science and Catalysis.
[1] "Unravelling Electronic Trends in O* and OH* Surface Adsorption in the MO2 Transition-Meta Oxide Series"; Benjamin M. Comer, Jiang Li, Frank Abild-Pedersen, Michal Bajdich, Kirsten Winther, 2022, (ACS J. Phys. Chem C.,)
[2] “Predicting O* and OH* Surface Adsorption on Transition Metal Oxides from Bulk Structure”; Benjamin M. Comer, Neha Bothra, Jaclyn Lunger, Frank Abild-Pedersen, Michal Bajdich, Kirsten Winther, Manuscript under preparation.