Scientists from Tokyo Tech have unveiled Ba2LuAlO5, a new material showing great promise as a proton conductor, potentially heralding a brighter future for protonic ceramic fuel cells (PCFCs).
Without the need for any additional chemical modifications, this innovative material demonstrates significant proton conductivity, as evidenced by both experimental and molecular dynamics simulations. Such a discovery could potentially lead us towards safer and more energy-efficient technologies.
Sustainability is highly dependent on our methods of energy generation. The scientific community globally is driven by the goal of replacing traditional, environmentally damaging energy sources like coal and oil with safer, more efficient alternatives. Among the prospective solutions, fuel cells have progressively gained popularity since the 1960s for their ability to generate electricity through electrochemical reactions.
The most common fuel cells, based on solid oxides, come with a significant downside: their high operating temperatures, often exceeding 700 °C. This has led many researchers to shift their focus towards PCFCs, which employ unique ceramics to conduct protons (H+), rather than oxide anions (O2−). Operating at considerably lower temperatures between 300 and 600 °C, PCFCs can offer a stable energy supply at reduced cost compared to their conventional counterparts. However, the dearth of known materials with acceptable proton-conducting performance has been a bottleneck for progress in this area.
In pursuit of a solution to this dilemma, a research team, including Professor Masatomo Yashima from Tokyo Tech, embarked on a search for viable proton conductor candidates for PCFCs. Their recent study in Communications Materials revealed the extraordinary properties of Ba2LuAlO5, a novel hexagonal perovskite-related oxide, which has shed new light on the dynamics of proton conduction.
Proton-Conducting Ba2LuAlO5: A New Material for Revolutionizing Fuel Cell Technology
In their quest for compounds with numerous intrinsic oxygen vacancies, Prof. Yashima and his team discovered Ba2LuAlO5. Earlier studies underlining the crucial role of these vacancies in proton conduction served as a catalyst for this research. Testing of Ba2LuAlO5 samples unveiled its impressive proton conductivity at low temperatures – specifically, 10‒2 S cm‒1 at 487 °C and 1.5×10‒3 S cm‒1 at 232 °C – without necessitating any additional chemical enhancements such as doping.
Eager to understand the reasons behind this unusual property, the team employed molecular dynamics simulations and neutron diffraction experiments. Their research unveiled two key attributes of Ba2LuAlO5. Firstly, compared to analogous materials, this oxide has a high capacity for water (H2O) absorption, resulting in the formation of Ba2LuAlO5.0.5H2O.
This substantial hydration, which takes place within two antithetical AlO4 tetrahedra layers, is facilitated by a high count of intrinsic oxygen vacancies in the hexagonal close-packed h’ BaO layers. Consequently, the elevated water content of the oxide amplifies its proton conductivity through various mechanisms, including an increase in proton concentration and the promotion of proton hopping.
The second salient characteristic pertains to the way protons traverse Ba2LuAlO5. The team’s simulations indicated that protons predominantly diffuse along the interfaces of LuO6 layers, which create cubic close-packed c BaO3 layers, rather than moving through the AlO4 layers.
As Prof. Yashima elucidates, this knowledge could prove pivotal in the quest for other proton-conducting substances:
This “work provides new design guidelines that open up unexplored avenues for the development of higher-performance proton conductors in the future.”
In forthcoming investigations, the researchers anticipate uncovering additional proton-conducting materials inspired by Ba2LuAlO5.
“By modifying the chemical composition of Ba2LuAlO5, further improvements in proton conductivity can be expected,” adds Prof. Yashima, “For example, the perovskite-related oxide Ba2InAlO5 may also exhibit high conductivity since its structure is quite similar to that of Ba2LuAlO5.”
Ultimately, the prospects for PCFCs appear optimistic, signaling a promising future for sustainable energy generation technologies as well.
Source: 10.1038/s43246-023-00364-5
Image Credit: Prof.M.Yashima, Tokyo Institute of Technology