Low-concentration HCl gas mixtures in H₂: Preparation and analysis

Measuring hydrogen chloride (HCl) impurities in hydrogen (H 2 ) produced by alkaline electrolysers is crucial in current “green” hydrogen systems. It aims to develop new gas standards and analytical methods, integrating both online and onsite monitoring and calibration at alkaline electrolyser facilities. These efforts are fundamental for setting industry-standard metrological practices that ensure reliable and consistent monitoring of hydrogen quality. Following strict standards such as ISO 14687:2019, which sets the quality requirements for hydrogen fuel and defines permissible contaminant levels like hydrogen chloride (HCl), highlights the importance of these initiatives. This study at Spanish Metrology Institute (CEM) aims to establish advanced capabilities for preparing and detecting hydrogen chloride (HCl) in hydrogen matrix mixtures at μmol/mol levels and below, as part of projects EPM 21GRD05 Met4H2 and the national Hydrogen Project-PRTR. To validate the in-house method, static gravimetric mixtures of HCl in hydrogen were prepared and analysed over a concentration range from 5 μmol/mol to 1 000 μmol/mol, revealing that while both gravimetric and analytical values align quite well at high concentrations, analytical measurements at lower levels report reduced HCl values-likely due to losses during successive dilutions.