Solid-state batteries and fuel cells one step closer with new hydride ion conductor

Researchers led by Genki Kobayashi at the RIKEN Cluster for Pioneering Research in Japan has achieved a significant breakthrough in the development of a solid electrolyte capable of transporting hydride ions (H−) at room temperature.

This advancement brings us closer to realizing the practical benefits of hydrogen-based solid-state batteries and fuel cells, including enhanced safety, efficiency, and energy density. These factors are crucial for the progression toward a viable hydrogen-based energy economy. The findings of the study were published in the journal Advanced Energy Materials.

For hydrogen-based energy storage and fuel to gain widespread acceptance, it must meet criteria such as safety, high efficiency, and simplicity. The current hydrogen-based fuel cells used in electric cars operate by allowing hydrogen protons to move through a polymer membrane from one end of the fuel cell to the other when generating energy.

Efficient and rapid hydrogen movement in these fuel cells necessitates the presence of water, requiring continuous hydration of the membrane to prevent drying out. This introduces complexity and cost to battery and fuel cell design, limiting the practicality of a next-generation hydrogen-based energy economy. Researchers have been striving to find ways to conduct negative hydride ions through solid materials, particularly at room temperature, to address this challenge.

The breakthrough has now been achieved. Kobayashi states, “We have achieved a true milestone. Our result is the first demonstration of a hydride ion-conducting solid electrolyte at room temperature.”

The team focused on lanthanum hydrides (LaH3-δ) for several reasons: easy release and capture of hydrogen, high hydride ion conduction, operation below 100°C, and a crystal structure. However, at room temperature, the number of hydrogens attached to lanthanum fluctuates between 2 and 3, hindering efficient conduction. This challenge, known as hydrogen non-stoichiometry, was the primary obstacle addressed in the new study. By replacing some lanthanum with strontium (Sr) and adding a small amount of oxygen, with a basic formula of La1-xSrxH3-x-2yOy, the researchers achieved the desired results.

The team created crystalline samples of the material using ball-milling and annealing. Testing at room temperature revealed the material’s ability to conduct hydride ions at a high rate. Further tests in a solid-state fuel cell made from the new material and titanium, with variations in strontium and oxygen amounts, demonstrated complete 100% conversion of titanium to titanium hydride, or TiH2, with an optimal strontium value of at least 0.2. This implies minimal waste of hydride ions.

“In the short-term, our results provide material design guidelines for hydride ion-conducting solid electrolytes,” Kobayashi notes. “In the long-term, we believe this is an inflection point in the development of batteries, fuel cells, and electrolytic cells that operate by using hydrogen.”

The next phase involves enhancing performance and developing electrode materials capable of reversibly absorbing and releasing hydrogen. This advancement would enable the rechargeability of batteries and facilitate the storage and controlled release of hydrogen, meeting the requirements for practical hydrogen-based energy applications.

Source: RIKEN

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