The Trujillo research group at Trinity’s School of Chemistry have conducted an investigation into metallic compounds that will be needed to store hydrogen fuel as we move towards greener energy sources. The team used quantum methodology to investigate the hydrogen storage capacity of various metal hydrides.
Reducing dependence on fossil fuels is a key element of the fight against climate change. An alternative fuel that could replace non-renewable options, particularly for transportation, is hydrogen. The gas can be produced using renewable energy and it then stores that energy for later use, most often in portable use-cases such as transportation. When the hydrogen is burnt in the presence of oxygen, its only byproduct is water.
We have already begun to see the introduction of hydrogen fuel cell vehicles including passenger cars and buses, including in Ireland. In July, the National Transport Authority and Bus Éireann unveiled three hydrogen fuel cell buses, which have begun service on the 105X route in Dublin.
“Among the greatest challenges facing humanity is the growing need to stop global warming and find more efficient and cleaner ways to produce energy. “ says Dr Cristina Trujillo, a research fellow at the School of Chemistry and the work’s senior author.
“As everybody already knows, the current production system and excessive use of fossil fuels is releasing much more CO2 into the atmosphere than is being absorbed naturally, which makes the creation of greener and more environmentally friendly alternatives a global priority.”
In order to use the large quantities of hydrogen required to fuel a bus for several journeys, however, it is essential to have an efficient way of storing the hydrogen. This is the work the quantum chemists of the Trujillo group have been undertaking, by exploring the hydrogen storage capabilities of a group of compounds called metal hydrides. Metal hydrides are combinations of metals and hydrogen, so if an appropriate accompanying metal is chosen, hydrogen can be stored in this form. The group has found that gold, silver and copper could be good candidates to do this.
“If the hydrogen was stored as metal hydride, it could be rapidly converted back to elemental hydrogen only when it is needed for use, providing a safer storage option.”
This could provide an alternative to current hydrogen fuel cell designs, which usually need to be maintained under great pressure, or cryogenically (at very low temperatures). Both of these come with certain risks. High-pressure gas can cause explosions if mishaps occur, and cryogenic gases can cause asphyxiation if they escape. If the hydrogen was stored as metal hydride, it could be rapidly converted back to elemental hydrogen only when it is needed for use, providing a safer storage option.
Greener fuels have been a hot topic of research for many years, says Trujillo: “For decades now many research groups across the world have put their efforts into this issue. One of the most studied alternatives has been hydrogen as a clean and CO2-free energy source, but it presents multiple problems due to its reactivity, and low density and stability.”
The group has been working on understanding regium bonds and how metals interact with other chemical species. This has allowed the group to better understand how hydrogen and the metals such as gold, silver and copper will interact.
“Our contribution here – made via quantum chemistry techniques – has been to show that gold, silver and copper hydride complexes are very likely to effectively retain hydrogen in a stable manner. We hope that this work will have multiple applications in time to come,” says Trujillo.