E-atom catalysts; reactivity; oxidation; stability; Pourbaix plots; Eh-pH diagram1. Introduction Single-atom catalysts (SACs) present the ultimate limit of catalyst utilization [1]. Since practically each atom possesses catalytic function, even SACs primarily based on Pt-group metals are appealing for practical applications. So far, the usage of SACs has been demonstrated for several catalytic and electrocatalytic reactions, which includes power conversion and storage-related processes which include hydrogen evolution reactions (HER) [4], oxygen reduction reactions (ORR) [7,102], oxygen evolution reactions (OER) [8,13,14], and other folks. Furthermore, SACs is often modeled relatively conveniently, because the single-atom nature of active sites enables the use of smaller computational models that may be treated without the need of any difficulties. Therefore, a combination of experimental and theoretical methods is frequently applied to explain or predict the catalytic activities of SACs or to design novel catalytic systems. As the catalytic component is Tetracosactide Protocol atomically dispersed and is chemically bonded for the help, in SACs, the help or matrix has an equally vital role as the catalytic element. In other words, a single single atom at two various supports will in no way behave the identical way, plus the behavior when compared with a bulk surface may also be unique [1]. Looking at the present study trends, understanding the electrocatalytic properties of different components relies around the results with the physicochemical characterization of thesePublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Copyright: 2021 by the authors. Licensee MDPI, Basel, Switzerland. This short article is an open access article distributed beneath the terms and situations in the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Catalysts 2021, 11, 1207. https://doi.org/10.3390/catalhttps://www.mdpi.com/journal/catalystsCatalysts 2021, 11,2 ofmaterials. Several of those characterization methods operate beneath ultra-high vacuum (UHV) circumstances [15,16], so the state with the catalyst under operating situations and through the characterization can hardly be the exact same. Moreover, prospective modulations under electrochemical situations can cause a alter in the state in the catalyst when compared with under UHV conditions. A well-known example may be the case of ORR on platinum surfaces. ORR IACS-010759 Purity & Documentation commences at potentials exactly where the surface is partially covered by OHads , which acts as a spectator species [170]. Altering the electronic structure in the surface and weakening the OH binding improves the ORR activity [20]. Furthermore, the same reaction can switch mechanisms at very higher overpotentials in the 4e- towards the 2e-mechanism when the surface is covered by underpotential deposited hydrogen [21,22]. These surface processes are governed by potential modulation and can’t be observed applying some ex situ surface characterization technique, for instance XPS. Having said that, the state of the electrocatalyst surface could be predicted applying the notion of the Pourbaix plot, which connects prospective and pH regions in which certain phases of a provided metal are thermodynamically stable [23,24]. Such approaches have been employed previously to understand the state of (electro)catalyst surfaces, particularly in mixture with theoretical modeling, enabling the investigation from the thermodynamics of different surface processes [257]. The notion of Pourbaix plots has not been widely make use of.
