Scandium superhighway paves way for low-temperature hydrogen fuel cells - Engineering - Energy & Green Tech

Digital image of the formation of proton transfer pathways in BaSnO₃ and BaTiO₃ thanks to high concentrations of scandium substitutions. Credit: Kyushu University / Yoshihiro Yamazaki

As global energy demand increases, researchers, industries, governments, and stakeholders are working together to develop new ways of meeting that demand. This is especially important as we address the ongoing climate crisis and transition away from fossil fuels.

One very promising type of energy generation is solid-oxide fuel cells (SOFCs). Unlike batteries, which release stored chemical energy as electricity, fuel cells convert chemical fuel directly into electricity and continue to do so as long as fuel is provided. A common type of fuel cell with which many people are familiar is hydrogen fuel cells, which convert hydrogen gas into energy and water.

While SOFCs are promising due to their high efficiency and long lifespan, one major drawback is that they require operation at high temperatures of around 700–800℃. Therefore, the utility of these devices would require costly heat-resistant materials.

In research published in Nature Materials, researchers at Kyushu University report that they have succeeded in developing a new SOFC with an efficient operating temperature of 300℃. The team expects that their new findings will lead to the development of low-cost, low-temperature SOFCs and greatly accelerate the practical application of these devices.

The heart of an SOFC is the electrolyte, a ceramic layer that carries charged particles between two electrodes. In hydrogen fuel cells, the electrolyte transports hydrogen ions (a.k.a. protons) to generate energy. However, the fuel cell needs to operate at extremely high temperatures to run efficiently.

"Bringing the working temperature down to 300℃ would slash material costs and open the door to consumer-level systems," explains Professor Yoshihiro Yamazaki from Kyushu University's Platform of Inter-/Transdisciplinary Energy Research, who led the study. "However, no known ceramic could carry enough protons that fast in such 'warm' conditions. So, we set out to break that bottleneck."

Electrolytes are composed of different combinations of atoms arranged in a crystal lattice structure. It's between these atoms that a proton would travel. Researchers have explored different combinations of materials and chemical dopants—substances that can alter the material's physical properties—to improve the speed at which protons travel through electrolytes.

"But this also comes with a challenge," continues Yamazaki. "Adding chemical dopants can increase the number of mobile protons passing through an electrolyte, but it usually clogs the crystal lattice, slowing the protons down. We looked for oxide crystals that could host many protons and let them move freely—a balance that our new study finally struck."

The team found that two compounds, barium stannate (BaSnO₃) and barium titanate (BaTiO₃), when doped with high concentrations of scandium (Sc), were able to achieve the SOFC benchmark proton conductivity of more than 0.01 S/cm at 300℃, a conductivity level comparable to today's common SOFC electrolytes at 600–700℃.

"Structural analysis and molecular dynamics simulations revealed that the Sc atoms link their surrounding oxygens to form a 'ScO₆ highway,' along which protons travel with an unusually low migration barrier. This pathway is both wide and softly vibrating, which prevents the proton-trapping that normally plagues heavily doped oxides," explains Yamazaki. "Lattice-dynamics data further revealed that BaSnO₃ and BaTiO₃ are intrinsically 'softer' than conventional SOFC materials, letting them absorb far more Sc than previously assumed."

The findings overturn the trade-off between dopant level and ion transport, offering a clear path for low-cost, intermediate-temperature SOFCs.

"Beyond fuel cells, the same principle can be applied to other technologies, such as low-temperature electrolyzers, hydrogen pumps, and reactors that convert CO₂ into valuable chemicals, thereby multiplying the impact of decarbonization. Our work transforms a long-standing scientific paradox into a practical solution, bringing affordable hydrogen power closer to everyday life," concludes Yamazaki. 

by Kyushu University

edited by Stephanie Baum, reviewed by Robert Egan 

Source: Scandium superhighway paves way for low-temperature hydrogen fuel cells