Design and optimization of Isochoric Differential Apparatus (IDA) to reduce uncertainty in H2 sorption process measurements

The quantification of hydrogen absorption and desorption in materials is a crucial step for the assessment of proper storage solutions and their applications. Unfortunately, volumetric instruments are in many cases affected by low accuracy due to several factors such as temperature uncertainty and misleading on calibration proceeding. In this work, we report the superior performance of a new kind of instrumental layout to characterize kinetics and thermodynamics properties of hydrogen storage materials. Hereby presented system is based on differential Sievert measurements, defined as Isochoric Differential Apparatus (IDA). IDA includes two coupled identical Sievert apparatus where pressure values are sampled in differential mode to compensate all temperature transient phenomena and nonlinear effects occurring during the gas expansion step that occurs during the measurements. A physical model to evaluate the sorbed gas at non-isothermal condition has been developed and reported. Detailed error analysis of the kinetic and thermodynamic models has been carried out considering a real gas. Palladium and Magnesium has been utilized as benchmark materials, to test the differential apparatus at ambient and high-temperature values > 300 °C). For both materials, kinetic and thermodynamic properties have been acquired by the differential layout in well agreement with reference data and with a higher accuracy than classic Sievert instrument, involving in identical size of expansion volume. This work demonstrates as the differential layout allows to reduce uncertainty in hydrogen sorption measurement exploiting the full accuracy of equipped transducers. At this level of performance, the impact of calibration procedures and the approach for the estimation of compressibility factor become extremely important to further reduce uncertainty on sorption measurements.