Providing traceability to humidity sensors in the hydrogen supply chain

Hydrogen is a promising energy vector for transport, industry, and energy storage. However, to promote its use, hydrogen must meet strict quality requirements along with its entire value chain, from production to storage, distribution and end-use. Water vapour is one of the key impurities for hydrogen quality control, and its online and on-site measurement is particularly challenging. Several humidity sensors based on different working principles (e.g. chilled mirrors, impedance sensors, quartz microbalance) are available on the market to reply to different industrial applications’ need both in terms of water vapour amount fraction and working pressure. Such sensors are usually calibrated in gases other than hydrogen such as air or nitrogen at pressure conditions different from those encountered in real-life applications. To provide traceability to humidity sensors in hydrogen at pressure above the ambient one and improve the uncertainty in the water vapour measurement, at INRiM a humidity generator able to generate a moist hydrogen stream with a water vapour mole fraction between 0.5 µmol/mol and 50 µmol/mol over a wide absolute pressure range from 0.2 MPa to 5.5 MPa was designed, developed and assessed. Using the INRiM humidity generator some commercially available aluminium oxide sensors were calibrated in nitrogen and hydrogen at pressure up to 3 MPa and in the water vapour mole fraction range down to 0.5 µmol/mol. Moreover, a selection of these sensors was tested in the field at two different sites. In this works the results of the sensors calibration and their application in the field are presented. This work has received funding from the European Partnership on Metrology programme under the grant EPM 21GRD05 Met4H2 co-financed by the Participating States and the European Union and from the Clean Hydrogen Partnership under the grant no 101101540 THOTH2 - HORIZON-JTI-CLEANH2-2022-1 co-financed by the European Union’s Horizon Europe Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research.