The desire to reduce carbon emissions is placing more and more importance on the need to find innovative energy sources. One such source that has considerable potential is hydrogen (H2), and unlike hydrocarbons such as petroleum, it can be easily produced from renewable sources. In addition, H2 does not cause pollution and produces only water as a by-product of combustion. However, if H2 is to be used as a replacement fuel, then there should be an infrastructure to facilitate its safe and cost-effective transport, storage, and distribution.
This article describes a study of novel hydrogen storage materials, where temperature programed techniques were used to investigate the hydrogen desorption profiles from a wide range of materials. Since it was imperative to measure the amount of hydrogen desorbing from the sample, the article also presents the results showing how the system was reliably calibrated.
A system was required to study the hydrogen storage properties of certain new materials. This system could be reliably calibrated to collect reproducible data. Moreover, to ensure proper activation of samples, there should be a good solid/gas phase interaction.
The hydrogen storage properties should be established using temperature programed techniques, for example, temperature programed desorption (TPD). Hiden CATLAB integrated microreactor-mass spectrometer system was used to perform these studies.
CATLAB Microreactor - Mass Spectrometer
The Hiden CATLAB is a microreactor system that is particularly designed for use with a mass spectrometer. The reactor module features a fast response furnace (Tmax 1000 ˚C) and can be configured for both manual and automatic operations. The MS module (QIC-20) includes a 200 amu MS, while the QIC inlet offers ultra-fast, high response sampling of evolved or desorbed species. Thanks to the inlet’s dual rotary pump design, the QIC – 20 is perfect for H2 desorption measurements. Here, the inlet’s bypass line is pumped independently by a single rotary pump and this prevents light gases such as He and H2 permeating through the turbo pump and into the main mass spectrometer chamber affecting results.
CATLAB Microreactor System
Calibration of CATLAB System
- The TPD-MS system needed initial calibration for H2 to allow the collection of quantitative H2 emission data
- This was realized by the thermal decomposition of TiH2, which releases 40.04% H2 by weight on heating
- Different quantities of TiH2 were introduced into the CATLAB system to provide the following calibration curve
Figure 1. Calibration Using TiH2 Decomposition.
Effect of Simultaneous Emission of Other Ions
- TiH2 was mixed with calcium oxalate to ensure that the measured H2 was not influenced by other species being emitted simultaneously
- The CO emission from calcium oxalate takes place at a similar temperature to that of H2 from TiH2, ca. 520 ˚C.
- There was no effect on the H2 signal - the data fit is displayed on the calibration curve (data point is circled in Figure 1).
Figure 2. Calcium Oxalate Decomposition.
Figure 3. Simultaneous CO and H2 Desorption.
H2 Desorption from Hydrogen Storage Materials
Based on the results from the calibration experiments, the system is sensitive and reproducible enabling confidence in the H2 desorption results produced from the hydrogen storage materials that were developed during this project. Two H2 desorption profiles from typical materials are shown below.
Figure 4. H2 Desorption Profile from Sample 1.
Figure 5. H2 Desorption Profile from Sample 2.
- The effects of D2 on the samples were also investigated
- As D2/HD is not naturally present in the materials, this would also indicate the efficiency of gas-solid mixing in the reactor
Figure 6. H2/D2 and HD Desorption Profile.
The above analyses prove that the Hiden CATLAB TPD-MS system can differentiate between low levels of species of 1 amu difference. These results are vital as they demonstrated the interaction between the D2 and the samples in the reactor system.
In brief, the Hiden CATLAB microreactor-mass spectrometer system shows excellent sensitivity, linearity, and reproducibility in hydrogen desorption measurements and is suitable for determining the hydrogen storage properties of a wide range of materials.
This work was funded by ITI Energy (Scotland).
This information has been sourced, reviewed and adapted from materials provided by Hiden Analytical.
For more information on this source, please visit Hiden Analytical.