E-atom catalysts; reactivity; oxidation; stability; Pourbaix plots; Eh-pH diagram1. Introduction Single-atom catalysts (SACs) present the

E-atom catalysts; reactivity; oxidation; stability; Pourbaix plots; Eh-pH diagram1. Introduction Single-atom catalysts (SACs) present the ultimate limit of catalyst utilization [1]. Considering the fact that practically each atom possesses catalytic function, even SACs primarily based on Pt-group metals are appealing for practical applications. So far, the use of SACs has been demonstrated for various catalytic and electrocatalytic reactions, including energy 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 others. Furthermore, SACs can be modeled relatively quickly, as the single-atom nature of active sites enables the use of smaller computational 5-Propargylamino-ddUTP Data Sheet models which can be treated with no any troubles. Therefore, a mixture of experimental and theoretical techniques is frequently made use of to clarify or predict the catalytic activities of SACs or to design novel catalytic systems. As the catalytic element is atomically BI-425809 Protocol dispersed and is chemically bonded to the assistance, in SACs, the assistance or matrix has an equally critical part because the catalytic component. In other words, a single single atom at two diverse supports will never ever behave the exact same way, plus the behavior in comparison to a bulk surface may also be different [1]. Looking at the existing analysis trends, understanding the electrocatalytic properties of distinct materials relies on the outcomes from 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 article is an open access short article distributed under the terms and circumstances of your Inventive 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. Numerous of these characterization tactics operate beneath ultra-high vacuum (UHV) situations [15,16], so the state in the catalyst under operating conditions and throughout the characterization can hardly be the same. Moreover, possible modulations below electrochemical conditions can cause a change inside the state in the catalyst when compared with beneath UHV conditions. A well-known instance will be the case of ORR on platinum surfaces. ORR commences at potentials exactly where the surface is partially covered by OHads , which acts as a spectator species [170]. Changing the electronic structure on the surface and weakening the OH binding improves the ORR activity [20]. Moreover, exactly the same reaction can switch mechanisms at extremely higher overpotentials from the 4e- for 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 noticed employing some ex situ surface characterization strategy, such as XPS. Nonetheless, the state with the electrocatalyst surface might be predicted working with the concept of the Pourbaix plot, which connects prospective and pH regions in which specific phases of a offered metal are thermodynamically steady [23,24]. Such approaches have been made use of previously to know the state of (electro)catalyst surfaces, especially in mixture with theoretical modeling, enabling the investigation on the thermodynamics of diverse surface processes [257]. The idea of Pourbaix plots has not been widely utilize.