© 2016 Portuguese Society of Materials (SPM). Published by Elsevier España, S.L.U. All rights reserved. http://dx.doi.org/10.1016/j.ctmat.2017.01.002 Ciência & Tecnologia dos Materiais 28 (2016) 99–105 ScienceDirect Available online at www.sciencedirect.com http://ees.elsevier.com/ctmat Special Issue on New Challenges in Energy Materials Instrumentation and characterization of materials for hydrogen storage Edivagner S. Ribeiro * , João M. Gil * CFisUC, Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal Abstract In order to identify and follow the challenges in the use of materials with the capacity to absorb hydrogen for energy storage, many groups address a diversity of issues, where the need to study the properties of the material upon absorbing hydrogen is always present. Appropriate equipment and techniques are needed: besides the use of classical systems, many research groups identified recently the need to study in more detail the properties related to the macroscopic changes of volume of the hydride powder as hydrogen content is cycled. In this article, we present the equipment and techniques developed by our group: after the classical volumetric systems, we addressed the problem of volumetric changes by building a novel coaxial capacitive system. This system measures the volume and porosity of a small amount of free hydride powder as a function of hydrogen content, after applying a complex deconvolution algorithm on the primary AC electric measurements. © 2016 Portuguese Society of Materials (SPM). Published by Elsevier España, S.L.U.. All rights reserved. Keywords: energy storage; hydrogen storage; characterization of materials; properties of hydride materials. 1. Introduction * Hydrogen is recognized as an excellent means of carbon-free high-density energy storage with well- identified potential applications in energy technologies when integrated with renewable resources at various scales of size and geographic distribution. Government agencies recognize the importance of hydrogen in this context, e.g. by defining related clear objectives within the current European Program Horizon 2020 [1,2]. Hydrogen can be produced by electrolysis using renewable primary sources [3, 4]; it can then be stored for later use in fuel cells, where the only generated residue is water. It can also be the fuel of internal combustion or turbine engines [5]. When burned in a pure oxygen environment, the only products are heat and water. Burning hydrogen in the atmosphere forms * Corresponding authors. E-mail addresses: edivagner@gmail.com (E.S. Ribeiro), jmgil@fis.uc.pt (J.M. Gil). some nitrogen oxides. Still, the burning of hydrogen produces fewer pollutants than fossil fuels. If applied in the automotive sector, it would change the landscape of greenhouse gas emissions, especially in urban areas. Among the challenges in the introduction of hydrogen as an energy vector, a key point is the development of efficient and safe storage means and the related technologies [3,5]. Hydrogen can be stored as a gas, liquid or in solid medium. The latter method best meets safety and volumetric energy density requirements. Nevertheless, storage in solid has several limiting important issues that must be resolved before its application, such as changes in the powder bed morphology (volume, grain size, compaction, and agglomeration) and chemical and kinetic degradations as hydrogen is cycled. Many solid media have been explored in the search for high-capacity or high-density hydrogen storage, from intermetallic compounds of various structures to lighter materials, such as carbon nanostructures or microporous materials, zeolites and MOFs [3,4]. Composites that cross those materials groups have