Comparison of electrical energy efficiency of atmospheric and high-pressure electrolysers

Efforts are being made to produce highly pressurised electrolysers to increase the overall energy efficiency by eliminating mechanical compression. However, in-depth modelling of electrolysers suggests that electrolysis at atmospheric pressure is electrically more energy efficient if parasitic energy consumption and gas losses are incorporated in both cases. The reversible cell voltage increases with increasing pressures. The electrode activation and Ohmic losses, leakage current and inevitable heat losses increase the electrolysis voltage beyond the thermoneutral voltage and consequently heat removal from the stack becomes essential. The expected gas loss at various operating pressures is incorporated to reveal the energy consumption that would occur in practice. Comparison of total energy consumption at various operating pressure up to 700 atm is performed and atmospheric electrolysers are found more efficient at all levels. Practical considerations such as corrosion, hydrogen embrittlement, operational complexity, dynamic response and cost are less favourable for pressurised electrolysers. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.