A review on the characterization of hydrogen in hydrogen storage materials

In order to realize a low-carbon hydrogen economy, a continuous search for materials able to store hydrogen in the solid form has been actively carried out globally. The need to accurately characterize the hydrogen storage properties of a variety of materials, including the thermodynamic and kinetic information, is of paramount importance. However owning to the diversity of potential hydrogen storage materials, it is essential to select a proper technique for characterize hydrogen storage properties to avoid faulty results. This paper serves as a critical review on several techniques commonly employed to characterize hydrogen storage materials. In this context, the working principles, advantages and drawbacks, limitations of six categories of techniques - Sieverts method, gravimetric method, secondary ion mass spectrometry, thermal desorption spectroscopy, neutron scattering and electrochemical techniques - are described and reviewed. It can be seen that Sieverts method is a powerful tool for metal hydride samples under normal testing regime. Gravimetric method can be used to investigate the hydrogen storage of porous samples since it normally suffers less from the sample volume uncertainty, however careful buoyancy correction must be applied to avoid faulty results. Secondary ion mass spectroscopy and thermal desorption spectroscopy can be used to study the surface/subsurface hydrogen profile and thermodynamic/kinetic properties of gas desorption of sample, respectively, providing that these samples are stable under vacuum. Neutron scattering is capable of investigating varies types of information including structural, diffusion and hydrogen dynamics of host material under in-stiu environment, although the neutron resources is not always accessible for most researchers. Electrochemical method can be used to study thermodynamic/kinetic properties for both thin film and bulk samples, but it may not be applicable to samples with low corrosion resistance and high plateau pressure.