Rapid Screening of Mechanistic Pathways for Oxygen‐Reduction Catalysts

Abstract

Oxygen reduction reaction (ORR) corresponds to the limiting process in fuel cells to convert gaseous hydrogen and oxygen from the air into electricity. Most commonly, electronic structure calculations in the density functional theory (DFT) approximation are applied to comprehend the elementary reaction steps on the atomic scale, including the identification of limiting reaction steps and approximation of electrocatalytic activity. A major challenge in the modeling of the ORR refers to the complexity of the mechanistic pathways given that a plethora of different descriptions, ranging from the mononuclear to OOH dissociation mechanisms, dissociative and oxide pathways, have been reported in the literature. In the present work, the adsorption free energy of the *OH intermediate, ΔG 1 , is introduced as an effective descriptor for rapid screening of ORR mechanisms. By applying a rigorous thermodynamic analysis in conjunction with a descriptor-based approach, it is demonstrated how the calculation of a single binding energy in terms of ΔG 1 can be used to identify the energetically favored mechanistic description for any ORR catalyst by analyzing the location of the material in the volcano plot. The introduced procedure may support future DFT-based studies in that the preferred pathway is not missed when modeling the fourelectron ORR by a binding-energy approach.

On the concept of metal–hydrogen peroxide batteries: improvement over metal–air batteries?

“…[24][25][26][27] For the 4e À ORR, the mononuclear, electrochemical *OOH dissociation, and chemical *OOH dissociation mechanisms are accounted for as these pathways have been shown to govern the volcano curve of the ORR. 28,29 The 4e À OER is described by the mononuclear and *OOÁ Á ÁOO* recombination mechanisms, as recently reported by Binninger et al, 30 emphasizing that the *OOÁ Á ÁOO* recombination mechanism is energetically favored over the mononuclear description at the volcano apex. 31 For the PRR, PFR, 2e À ORR, and 2e À OER a single mechanism with one intermediate is taken into account, following previous theoretical works on the same topic.…”

“…The free-energy changes of the elementary steps are analyzed by a rigorous thermodynamic framework in that they are related to two descriptors, namely the adsorption free energy of the *OH intermediate, DG 1 , and the scaling-relation intercept, SRI, between the *OH and *OOH adsorbates. 28,29,31 This procedure is exemplary demonstrated for the mononuclear OER mechanism in the following:…”

General Pyrolysis for High-Loading Transition Metal Single Atoms on 2D-Nitro-Oxygeneous Carbon as Efficient ORR Electrocatalysts

“…This evidence suggests that these active sites facilitate more efficient ORR. To explain the general trend of the activity, the free energy change of *OH intermediate (Δ G *OH ) was chosen as a descriptor for the overpotential. − The nearly perfect volcano plot can be obtained where FeO-N 3 O is located on the top of the volcano, confirming that Δ G *OH is a good descriptor for the reaction (Figure e). Interestingly, a greater number of O-replacement to the in-plane N-coordination would increase the overpotential and lower the ORR activity, as seen from the trend going from Fe–N 4 , N 3 O–Fe to the lowest activity of ORR = −1.65 eV for N 2 O 2 –Fe.…”

Two‐Dimensional Tetragonal Transition Metal Chalcogenides for High Performance Oxygen Evolution and Reduction: A DFT Study

“…This reaction mechanism is also called a mononuclear mechanism. In addition to the mononuclear mechanism, OER and ORR might also proceed via binuclear mechanisms and other complex multi‐step reaction pathways [33,34] . The investigation of these mechanisms could contribute to a comprehensive understanding of the kinetics and catalytic mechanisms underlying OER/ORR.…”