A new symbiotic CeH2.73/CeO2 catalyst was in situ induced in Mg-based hydrides, resulting in extremely reduced hydrogen desorption temperatures. More importantly, a spontaneous hydrogen release effect is revealed at the CeH2.73/CeO2 interface using in situ High-Resolution Transmission Electron Microscope (HRTEM) and ab-initio calculations.
Challenges in Applying Hydrogen Storage Materials
Using catalysts/additives to destabilize hydrides of high hydrogen storage density, for example MgH2 with 7.6 wt.%-H and desorption temperature as high as 300-400 °C, is considered to be one of the most vital strategies to overcome the problem of applying hydrogen storage materials in technologies related to hydrogen energy. In spite of tremendous efforts, the development of catalysts/additives with high catalytic activity and effortless doping continues to be a major challenge.
Novel Hydrogen Pump
This article presents a simple method to induce a novel symbiotic CeH2.73/CeO2 catalyst in Mg-based hydrides, which has the potential of being mass produced. The first step is to hydrogenate the amorphous Mg-Ce-Ni alloy in order to obtain a multiphase composite of MgH2, CeH2.73 and Mg2NiH4. The second step is to oxidize the hydrogenated sample to produce CeO2 from CeH2.73.
In addition to this, the article also demonstrates a spontaneous hydrogen release effect at the CeH2.73/CeO2 interface, which brings about a dramatic increase of catalytic activity compared with either the CeH2.73 or CeO2 catalyst alone. TPD-MS analysis was carried out on a Hiden QIC-20 mass spectrometer, as shown in Figure 1a. With the increase of the CeH2.73 to CeO2 ratio, the hydrogen desorption temperature initially decreases and then increases after reaching the trough at the molar ratio of 1:1. It is possible for the catalytic activity of the symbiotic CeH2.73/CeO2 to have a close relationship with their interface density, which reaches the maximum when molar ratio of CeH2.73 to CeO2 is 1:1, however, the mechanism is yet to be well understood. The lowest dehydrogenation onset temperature is just ~210 °C in the presence of the symbiotic CeH2.73/CeO2, which is ~210 °C lower than that of conventional MgH2.
Figure 1. (a) DSC and TPD-MS curves of the symbiotic CeH2.73/CeO2 doped MgH2, heating rate of 2 K/min. (b) In situ HRTEM images of the dehydrogenation process, boundary between CeH2.73 and CeO2 is roughly drawn with a dash line at the beginning of hydrogen desorption.
High-Resolution Transmission Electron Microscope
Using in situ High-Resolution Transmission Electron Microscope (HRTEM) Figure 1 (b), the dynamic boundary evolution during hydrogen desorption was seen in the symbiotic CeH2.73/CeO2 at atomic resolution.
The boundary region experiences severe distortions and the distorted areas fluctuates wave-like during hydrogen desorption, indicating that the interface region of the symbiotic nanocrystals experience structural evolution at the atomic scale, which most likely plays an important role for the release of hydrogen in dehydrogenation. By combining the ab-initio calculations, which show major reduction of the formation energy of hydrogen vacancy in the CeH2.73/CeO2boundary region when compared to those in the bulk MgH2 and CeH2.73, the article demonstrates that the exceptional catalytic activity can be due to the spontaneous hydrogen release effect at the CeH2.73/CeO2 interface.
Project Summary by:
School of Materials Science and Engineering
South China University of Technology
P R China
Paper Reference: Huai-Jun Lin, et al.(2014) “Symbiotic CeH2.73/CeO2 catalyst: A novel hydrogen pump” Nano Energy 9, 80-87
This information has been sourced, reviewed and adapted from materials provided by Hiden Analytical.
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