Citation: Santos, A.L.; Cebola, M.J.; Antunes, J.; Santos, D.M.F. Insights on the Performance of Nickel Foam and Stainless Steel Foam Electrodes for Alkaline Water Electrolysis. Sustainability 2023, 15, 11011. https://doi.org/10.3390/ su151411011 Academic Editor: Andrea G. Capodaglio Received: 28 April 2023 Revised: 5 July 2023 Accepted: 12 July 2023 Published: 13 July 2023 Copyright: © 2023 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/). sustainability Article Insights on the Performance of Nickel Foam and Stainless Steel Foam Electrodes for Alkaline Water Electrolysis Ana L. Santos 1,2 , Maria João Cebola 3,4,5 , Jorge Antunes 1 and Diogo M. F. Santos 2, * 1 TecnoVeritas—Serviços de Engenharia eSistemas Tecnológicos, Lda, 2640-486 Mafra, Portugal; ana.l.santos@tecnico.ulisboa.pt (A.L.S.); jorge.antunes@tecnoveritas.net (J.A.) 2 Center of Physics and Engineering of Advanced Materials, Laboratory for Physics of Materials and Emerging Technologies, Chemical Engineering Department, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 3 CBIOS—Center for Research in Biosciences & Health Technologies, Universidade Lusófona de Humanidades e Tecnologias, Campo Grande 376, 1749-024 Lisbon, Portugal; mcebola@egasmoniz.edu.pt 4 CERENA—Centre for Natural Resources and the Environment, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal 5 CiiEM—Centro de Investigação Interdisciplinar Egas Moniz, Campus Universitário, Quinta da Granja, 2829-511 Caparica, Portugal * Correspondence: diogosantos@tecnico.ulisboa.pt Abstract: Green hydrogen production seems to be the best route to achieve a sustainable alternative to fossil fuels, as hydrogen has the highest energy density on a mass basis and its combustion does not produce greenhouse gases. Water electrolysis is the method of choice for producing green hydrogen. Among commercially available water electrolysis systems, alkaline water electrolysis (AWE) is the most well-established technology, which, nevertheless, still needs to improve its efficiency. Since the electrodes’ performance is of utmost importance for electrolysis efficiency, nickel foam (NF) and stainless steel foam (SSF) electrodes were analyzed via voltammetry to validate their catalytic activity toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 30 wt.% NaOH electrolyte solution. Moreover, at a current density of 50 mA cm −2 , the NF and the SSF exhibited good stability, with the potential for HER and OER stabilizing at −0.5 V and 1.6 V vs. reversible hydrogen electrode. A lab-scale electrolyzer attained current densities of 10, 20, and 50 mA cm −2 at small cell voltages of 1.70 V, 1.80 V, and 1.95 V. The results validated NF and SSF as electrodes for a high-performance AWE electrolyzer, especially at higher temperatures. They ensured the progress for the project’s next stage, i.e., constructing an electrolyzer at a pilot scale. Keywords: alkaline water electrolysis; green hydrogen; high-efficiency electrolyzer; hydrogen evolution reaction; nickel foam; oxygen evolution reaction; stainless steel foam 1. Introduction Due to population increase, growing energy demand severely threatens the global economy, as well as the environment, consequently leading to climate change. For the past one hundred years, fossil fuels have been, by far, the principal source of energy. As these are non-renewable sources, and their consumption produces massive emissions of greenhouse gases (GHG), replacing them with alternative clean energy resources is imperative. Hydrogen is critical for developing clean and sustainable energy systems [1–4]. Yet, hydrogen represents a modest fraction of the energy mix, and only 4% of the global hydrogen supply comes from clean sources [5,6]. Water electrolysis leads among the methods that use renewable energy to produce hydrogen [7]. In fact, by definition, hydrogen can only be called green if produced by water electrolysis using renewable energy sources [8]. But for a hydrogen economy based on water electrolysis to thrive, the available technologies still require further improvement to Sustainability 2023, 15, 11011. https://doi.org/10.3390/su151411011 https://www.mdpi.com/journal/sustainability