Citation: Gebremariam, G.K.; Jovanovi´ c, A.Z.; Dobrota, A.S.; Skorodumova, N.V.; Pašti, I.A. Hydrogen Evolution Volcano(es)—From Acidic to Neutral and Alkaline Solutions. Catalysts 2022, 12, 1541. https://doi.org/ 10.3390/catal12121541 Academic Editor: Svetlana B. Štrbac Received: 12 November 2022 Accepted: 28 November 2022 Published: 30 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). catalysts Communication Hydrogen Evolution Volcano(es)—From Acidic to Neutral and Alkaline Solutions Goitom K. Gebremariam 1,2,† , Aleksandar Z. Jovanovi´ c 1,† , Ana S. Dobrota 1 , Natalia V. Skorodumova 3 and Igor A. Pašti 1, * 1 University of Belgrade–Faculty of Physical Chemistry, Studentski trg 12–16, 11158 Belgrade, Serbia 2 Department of Chemistry, Mai Nefhi College of Science, National Higher Education and Research Institute, Asmara 12676, Eritrea 3 Department of Materials Science and Engineering, School of Industrial Engineering and Management, KTH–Royal Institute of Technology, Brinellvägen 23, 100 44 Stockholm, Sweden * Correspondence: igor@ffh.bg.ac.rs; Tel.: +381-11-3336-625 † These authors contributed equally to this work. Abstract: As the global energy crisis continues, efficient hydrogen production is one of the hottest topics these days. In this sense, establishing catalytic trends for hydrogen production is essential for choosing proper H 2 generation technology and catalytic material. Volcano plots for hydrogen evolution in acidic media are well-known, while a volcano plot in alkaline media was constructed ten years ago using theoretically calculated hydrogen binding energies. Here, for the first time, we show that the volcano-type relationships are largely maintained in a wide range of pH values, from acidic to neutral and alkaline solutions. We do this using theoretically calculated hydrogen binding energies on clean metallic surfaces and experimentally measured hydrogen evolution overpotentials. When metallic surfaces are exposed to high anodic potentials, hydrogen evolution can be boosted or significantly impeded, depending on the type of metal and the electrolyte in which the reaction occurs. Such effects are discussed here and can be used to properly tailor catalytic materials for hydrogen production via different water electrolysis technologies. Keywords: hydrogen evolution reaction; catalytic trends; acidic media; neutral media; alkaline media 1. Introduction Hydrogen evolution reaction (HER) has always had a special place in electrochemistry, but nowadays, it has gained even more attention due to the global energy crisis. As hydrogen is sought as the fuel of the future, finding economical ways for its production would solve the existing problems. This particularly relates to green hydrogen production via water electrolysis, where renewable energy sources are used to produce high-purity hydrogen. However, green hydrogen is still rather expensive. Thus, finding new, efficient catalysts for its production is necessary. Understanding HER activity trends can help us in this search, and the best example is the HER volcano curve. In the original formulation, it was shown that HER exchange current densities were correlated with hydride formation energies of different metals [1]. Another formulation of HER volcano comes from the group of Nørskov et al. [2], where literature data for HER exchange current densities in acidic media were correlated to the theoretically calculated hydrogen binding energies. However, this approach was criticized [3], suggesting it was overly simplistic. Moreover, it was suggested that there was no volcano if oxide-covered metals were removed (W, Mo, Ta, Ti, and Nb from the “original” volcano) and that the reaction rate does not decrease for highly exothermic hydrogen adsorption [4]. Nevertheless, the HER volcano curve represents an appealing depiction of HER activity trends. Therefore, it is widely used in the community to search for new HER catalysts by pinpointing materials with optimal hydrogen binding energies, even Catalysts 2022, 12, 1541. https://doi.org/10.3390/catal12121541 https://www.mdpi.com/journal/catalysts