A team of Japanese researchers has developed a solid electrolyte that can transport hydride ions (H−) at room temperature. This achievement marks the start of the practical use of hydrogen-based batteries and fuel cells, with significant improvements in safety, efficiency and energy density.
The hydrogen challenge
The widespread use of hydrogen-based energy requires optimal safety, high efficiency and maximum simplicity. Hydrogen fuel cells, currently used in electric cars, work by allowing hydrogen protons to pass through a polymer membrane from one end of the cell to the other when generating electricity.
However, the efficient and rapid movement of hydrogen through these cells requires water, which means the membrane must be constantly hydrated to avoid drying out. This limitation increases the complexity and cost of battery and fuel cell design and limits the practicality of a next-generation hydrogen-based energy economy.
Scientists therefore looked for a way to pass negative hydride ions through solid materials, especially at room temperature. “We have reached a real milestone,” says Genki Kobayashi from RIKEN in Japan. “Our result is the first demonstration of a solid electrolyte that conducts hydride ions at room temperature. »
The solution: lanthanum hydrides
The team experimented with lanthanum hydrides (LaH3-δ) for several reasons: hydrogen can be released and captured relatively easily, conduction of hydride ions is very high, they can operate below 100 °C and have a crystalline structure. On the other hand, at room temperature, the number of hydrogen atoms bound to lanthanum fluctuates between 2 and 3, making efficient conduction impossible. This problem, called hydrogen nonstoichiometry, was the biggest obstacle overcome in the new study.
When researchers replaced part of it Lanthanum with strontium (Sr) and added a pinch of oxygen, for a basic formula of La1-xSrxH3-x-2yOy they got the expected results. They created crystalline samples of the material using a process called ball milling and then performed annealing. They examined the samples at room temperature and found that they could conduct hydride ions at high speeds.
Promising tests
They then tested the performance in a fuel cell Solid body made of new material and titanium, by varying the amounts of strontium and oxygen in the formula. At an optimal value of at least 0.2 strontium, they observed 100% complete conversion of titanium to titanium hydride or TiH2. This means that almost no hydride ions were wasted.
“In the short term, our results provide material design guidelines for hydride ion-conducting solid electrolytes,” adds Genki Kobayashi. “In the long term, we believe this is a turning point in the development of batteries, fuel cells and electrolytic cells powered by hydrogen. »
The next step is to improve performance and create electrode materials that can reversibly absorb and release hydrogen. This would enable charging of batteries as well as the storage and easy release of hydrogen on demand, a prerequisite for the use of hydrogen-based energy.
synthetic
The discovery by the research team in Japan marks an important step in the development of hydrogen-based technologies. By successfully transporting hydride ions at room temperature, they paved the way for a more practical and efficient use of hydrogen as an energy source. The next research steps will focus on improving performance and developing electrode materials that can reversibly absorb and release hydrogen.
For better understanding
What is a hydride ion?
A hydride ion is a hydrogen ion that has gained an electron and thereby acquired a negative charge.
Why is it important to transport hydride ions at room temperature?
Transporting hydride ions at room temperature simplifies the design of batteries and fuel cells and eliminates the need for a complex cooling system.
What is Hydrogen Nonstoichiometry?
Hydrogen nonstoichiometry is a phenomenon in which the number of hydrogen atoms bonded to another element fluctuates, making efficient conduction difficult.
What is ball milling?
Ball milling is a process designed to reduce the particle size of a material by subjecting it to impact with steel or ceramic balls.
What is glow?
Annealing is a thermal process designed to increase the ductility of a material and reduce the hardness by heating it to a certain temperature and then slowly cooling it.
References
Caption: Schematic representation of a solid-state fuel cell made from the new material and titanium. The result of the galvanostatic discharge reaction showed that the Ti electrode was completely hydrogenated to TiH2 for x ≥ 0.2. Photo credit: Riken
Article: “Electropositive metal doping in lanthanum hydride for the use of H-conducting solid electrolytes at room temperature” – DOI: 10.1002/aenm.202301993
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