energies Review Towards the Hydrogen Economy—A Review of the Parameters That Influence the Efficiency of Alkaline Water Electrolyzers Ana L. Santos 1,2, Maria-João Cebola 3,4,5 and Diogo M. F. Santos 2,* 1 TecnoVeritas—Serviços de Engenharia e Sistemas Tecnológicos, Lda, 2640-486 Mafra, Portugal;
[email protected] 2 Center of Physics and Engineering of Advanced Materials (CeFEMA), 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;
[email protected] 4 CERENA—Centre for Natural Resources and the Environment, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal 5 Escola Superior Náutica Infante D. Henrique, 2770-058 Paço de Arcos, Portugal * Correspondence:
[email protected] Abstract: Environmental issues make the quest for better and cleaner energy sources a priority. Worldwide, researchers and companies are continuously working on this matter, taking one of two approaches: either finding new energy sources or improving the efficiency of existing ones. Hydrogen is a well-known energy carrier due to its high energy content, but a somewhat elusive one for being a gas with low molecular weight. This review examines the current electrolysis processes for obtaining hydrogen, with an emphasis on alkaline water electrolysis. This process is far from being new, but research shows that there is still plenty of room for improvement. The efficiency of an electrolyzer mainly relates to the overpotential and resistances in the cell. This work shows that the path to better Citation: Santos, A.L.; Cebola, M.-J.; electrolyzer efficiency is through the optimization of the cell components and operating conditions.