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====Hydrogen generation technologies from water electrolysis: Present and future of high-pressure electrolyzers====
*'''Authors:''' Alfredo Ursúa (University of Navarra, Spain), Pablo Sanchis (University of Navarra, Spain)
*'''Contact email:''' pablo.sanchis@unavarra.es
*'''Scope:''' This paper describes the water electrolysis technology to produce clean hydrogen in a renewable energy-based grid. First, basic concepts concerning thermodynamics and electrochemistry of water electrolysis, with special attention to the influence of the temperature and pressure on the process, are explained both from a theoretical and practical point of view. Then, the two main types of electrolyzers, alkaline and PEM, are described and compared. After that, the technology used in atmospheric and pressurized electrolyzers is exposed and evaluated, and their strengths, weaknesses and trends for the coming years are analyzed. Commercial units of the different technologies offered by manufacturers are included in the analysis.