[High Pressure] How the Volumetric Technique Sorption Analyzer Works

The volumetric technique determines the amount of hydrogen adsorb or absorbed by a sample by monitoring the drop in hydrogen pressure in a fixed volume in direct contact with the sample. During the desorption process, the quantity of hydrogen released is determined by the increase in the hydrogen pressure, following evacuation of some or all of the hydrogen in the gas phase.

[High Pressure] Samples Pretreatment/Degassing and History

A sample’s history, including periods of storage, can have a significant effect on its sorption properties and so it is important that this is known and recorded, particularly if the results from two samples are to be compared. This was identified as one of the key problems in (volumetric) kinetic measurements.

[High Pressure] Sample Degassing Importance

Before any sorption experiment a material and the apparatus must be degassed to a certain extent. In the case of adsorbents this process is crucial in preparing the sample’s surface for adsorption. In general, it is necessary to begin an adsorption measurement with the surface in a state appropriate for the application for which the material is being considered. For hydrogen adsorption a ‘clean’ surface is required, although there may be exceptions, depending on the definition of a ‘clean’ surface.

[High Pressure] The Problems and Study of Hydrogen Storage

The search for potential hydrogen storage materials has recently been receiving a great deal of attention, as the hydrogen storage problem is one of the major issues that needs to be resolved if hydrogen is to become a viable energy carrier in the future.

[High Pressure] Hydrogen Adsorption Experimental Considerations for Volumetric and Gravimetric Methods

The following summary of the experimental considerations and error sources in the measurement of hydrogen absorption by hydrogen-absorbing materials using volumetric, or manometric, apparatus (the Sieverts Method) applies to measurements made in the temperature range from ambient to high temperatures in the region of 673 K.

[High Pressure] Capacity vs. Concentration in Hydrogen Storage

Before concentration and capacity can be discussed in depth, it is important to differentiate between capacity, a material property, and the concentration variable in hydrogen storage measurements. Concentration and capacity provide information about the hydrogen content of a sample.

[High Pressure] Eight Measurement Methods of Hydrogen Storage Systems

There are a number of measurement methods that can be used to investigate hydrogen storage materials and systems. Gravimetric and volumetric methods are the two primary methods and the most robust in terms of depth of analysis; temperature-programmed desorption, differential scanning calorimetry, and thermal gravimetric analysis are also used.

[High Pressure] Hydrogen Storage Materials Based on Physisorption of Molecular Hydrogen

Materials for hydrogen storage can be divided into two families: hydrides (hydriding alloys, molecular hydride complexes, amine complexes, and hydrocarbons) and physisorbed high-surface-area materials (carbon fullerenes, nano-tubes, metal-organic frameworks and aerogels).

[High Pressure] Hydrogen Storage Properties Measurement Purposes

Hydrogen storage properties measurements can be broken down into three basic categories: storage system level performance measurements, materials development measurements, and fundamental science measurements. It is important to understand the purpose of a particular experimental investigation before making measurements because the experimental setup and procedures can vary greatly depending on the purpose of the measurements and results and conclusions can be misleading if they are not presented in the proper context.

[High Pressure] Kinetics Measurements and Pressure-Composition-Temperature (PCT) Measurements for Hydrogen Storage

With respect to characterizing a material’s hydrogen storage performance there are two principal types of measurements, kinetics measurements and pressure-composition-temperature (PCT) measurements. Kinetics measurements can be considered the fundamental measurement of hydrogen storage because other types of measurement, including PCTs, are collections of several individual kinetics measurements.

[High Pressure] Hydrogen Storage Properties

A brief summary of the principal measured properties of hydrogen storage materials and systems, include capacity property, kinetics property, thermodynamics property and cycle-life property.

[High Pressure] Kinetics in Hydrogen Storage

For hydrogen storage, kinetics is generally taken to mean the rates of hydrogen sorption and desorption from a storage material occur. A primary difference between capacity and kinetics in reversible systems is that capacity measurements are theoretically taken at thermodynamic equilibrium, independent of the time required to reach equilibrium, while kinetics investigates how the material approaches equilibrium and what influences this approach.

[High Pressure] Hydrogen Storage Variables

All hydrogen storage properties are determined by the relationships between the variables: concentration, sample weight, temperature, pressure, cycle and time. Accurate measurement of direct variables is important for all hydrogen storage properties and perhaps more so for the determination of concentration than any other.

[High Pressure] Classification of Materials for Hydrogen Storage Materials Applications

Materials for hydrogen storage can be separated into different classes based on how they will be used in applications. In this sense there are three categories generally based on the energetics of storing hydrogen which we will designate as “Physisorption”, “On-board Reversible Hydrides”, and “Off-board Regenerable Hydrides” materials.

[High Pressure] Hydrogen Storage Capacity Measurement

Hydrogen capacity is the material property that has had the greatest focus of attention in the race to discover and improve the ultimate hydrogen storage material. While the other critical materials properties (kinetics, thermodynamics, stability, safety, cost and flavor) may have been pushed into the shadows by comparison, it is true that without a reasonably high capacity, a material can not be considered viable for on-board hydrogen storage.