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New proton conductor for next-generation proton ceramic fuel cells: Ba2LuAlO5

A team of researchers led by Tokyo Tech reports that the oxide Ba2LuAlO5 is a promising proton conductor for protonic ceramic fuel cells. Experiments show that this novel material has a remarkably high proton conductivity even without any additional chemical modifications, and molecular dynamics simulations reveal the underlying reasons. An open-access paper on the work is published in Communications Materials.

Proton conductors have found diverse applications, such as electrolytes in proton ceramic fuel cells, which require high ionic conductivity at low temperatures and high chemical stability. Here, we report the oxide, Ba2LuAlO5, which exhibits proton conductivities of 10−2 S cm−1 at 487 °C and 1.5 × 10−3 S cm−1 at 232 °C, high diffusivity and high chemical stability without chemical doping.

Ba2LuAlO5 is a hexagonal perovskite-related oxide with highly oxygen-deficient hexagonal close-packed h′ layers, which enables a large amount of water uptake x = 0.50 in Ba2LuAlO5·x H2O. Ab initio molecular dynamics simulations and neutron diffraction show the hydration in the h′ layer and proton migration mainly around cubic close-packed c layers existing at the interface of octahedral LuO6 layers. These results demonstrate that the high proton conduction allowed by the highly oxygen-deficient and cubic close-packed layers is a promising strategy for the development of high-performance proton conductors.

—Morikawa et al.

Typical solid oxide fuel cells have a notable drawback in that they operate at high temperatures, usually above 700 °C. Many scientists as a result have focused on protonic ceramic fuel cells (PCFCs) instead. These cells use special ceramics that conduct protons (H+) instead of oxide anions (O2−). Due to a much lower operating temperature in the range of 300 to 600 °C, PCFCs can ensure a stable energy supply at a lower cost, compared to most other fuel cells. Unfortunately, only a few proton-conducting materials with reasonable performance are currently known, which is slowing down progress in this field.

Professor Masatomo Yashima from Tokyo Institute of Technology (Tokyo Tech) and colleagues discovered Ba2LuAlO5 while focusing on finding compounds with a lot of intrinsic oxygen vacancies. This was motivated by the results of previous studies highlighting the importance of these vacancies in proton conduction.

Experiments on Ba2LuAlO5 samples revealed that this material has a high proton conductivity in its bulk at low temperatures even without additional chemical refinements such as doping.


Afterwards, the team sought to find out the underlying reasons for this property. Through molecular dynamics simulations and neutron diffraction measurements, they learned two important characteristics of Ba2LuAlO5. The first is that this oxide absorbs a lot of water (H2O), compared to other similar materials. This large water uptake, which occurs within two opposing layers of AlO4 tetrahedra, is made possible by a high number of intrinsic oxygen vacancies in the hexagonal close-packed h´ BaO layers. In turn, the oxide’s higher water content increases its proton conductivity through various mechanisms, such as higher proton concentration and enhanced proton hopping.

The second important characteristic is related to how protons move through Ba2LuAlO5. Simulations revealed that protons diffuse mainly along the interfaces of LuO6 layers, which form cubic close-packed c BaO3 layers, rather than through the AlO4 layers. This information could be critical in the search for other proton conducting materials.

The researchers expect to find other proton-conducting materials based on Ba2LuAlO5 in upcoming studies.

By modifying the chemical composition of Ba2LuAlO5 , further improvements in proton conductivity can be expected. For example, the perovskite-related oxide Ba2InAlO5 may also exhibit high conductivity since its structure is quite similar to that of Ba2LuAlO5.

—Prof Yashima


  • Morikawa, R., Murakami, T., Fujii, K. et al. (2023) “High proton conduction in Ba2LuAlO5 with highly oxygen-deficient layers.” Commun Mater 4, 42 doi: 10.1038/s43246-023-00364-5



Here is an analysis of the pros and cons of different types of fuel cells:

Of course this will not be of interest to those who seek to dismiss the whole field of technology ab initio.


Lu is Lutetium
from wiki " Pure lutetium metal is very difficult to prepare. It is one of the rarest and most expensive of the rare earth metals with the price about US$10,000 per kilogram, or about one-fourth that of gold."
So, the knowledge is the key - as they say in this paper:

"This information could be critical in the search for other proton conducting materials."


Hi Jim.

Your link is kinda 'glass half full/half empty!'

' Lutetium is not a particularly abundant element, although it is significantly more common than silver in the earth's crust. I'

They give the price as about that of silver, too.

That is expensive etc compared to other rare earths, but not compared to the likes of platinum, which is used in PEM electrolysers although not in SOFC

Maybe this will help spread the load and demand for materials for electrolysers?


It is curious.
They produce 25,000 tons of silver per year and 10 tons of lutetium per year - and yet the cost per kg is the same.
Perhaps if they tried to increase the supply, the price would go up, or perhaps the amount will increase naturally as more and more rare earths are used in magnets etc.


An SOFC can take natural gas directly no reform

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