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Introduction:
In the pursuit of clean and renewable energy, scientists worldwide have long sought after efficient energy storage solutions. Superionic conductors promise clean, renewable energy — at the right temperatures. These conductors, used as solid electrolytes in batteries and fuel cells, comprise solid materials in which ions move as fast as in liquids.
Solid materials that conduct lithium, sodium and hydrogen cations have been used in batteries and fuel cells. Under certain conditions, some of the materials transition to superionic states where ions move as fast as they do in liquids by skipping through the rigid crystal structure. This phenomenon is advantageous for chemical and energy conversions as it allows ions to move without a liquid or soft membrane to separate the electrodes. However, few solid-state materials can reach this state under ambient conditions.
Unlocking the Potential of Hydride Ions:
A significant breakthrough in this endeavor has been achieved by an international research team, marking a pivotal moment in the advancement of sustainable energy technologies. Published in Nature Materials, their groundbreaking research introduces the first-ever superionic conductor based on hydride ions, offering promising implications for the future of clean energy.
Several H− conductors have already been developed in recent years, including alkaline earth metal hydrides and oxyhydrides of alkaline earth and rare earth metals, which are known for fast hydrogen migration. But none of the materials developed could achieve superionic conduction at ambient conditions—until the DICP team took a new approach.
Superionic conductors, which facilitate the rapid movement of ions within solid materials, hold immense potential for applications in batteries and fuel cells. However, conventional superionic conductors face limitations in the intermediate temperature range, hindering their efficacy in energy conversion processes. To address this challenge, the research team focused on hydride ions, leveraging their unique characteristics to enhance ion conductivity at intermediate temperatures.
The Key to Enhanced Conductivity:
By synthesizing the oxyhydride compound, Ba1.75LiH2.7O0.9 (BLHO), the researchers achieved remarkable superionic conductivity in the target temperature range of 300-350°C. BLHO’s layered structure, comprising barium, lithium, hydrogen, and oxygen, was meticulously designed to optimize ion diffusion. Through a phase transition process, BLHO exhibits a consistent and high level of conductivity, showcasing its potential as a solid electrolyte for energy and chemical conversion devices.
Chinese Scientists Pioneer Room-Temperature Superionic Hydride Ion Conduction
Researchers at the Dalian Institute of Chemical Physics, affiliated with the Chinese Academy of Sciences, have achieved a remarkable milestone: the development of the world’s first superionic hydride ion conductor that operates at room temperature. This breakthrough holds immense promise for revolutionizing clean energy technologies and addressing pressing global challenges related to sustainability and environmental conservation.
Hydride ions (H-) have emerged as promising candidates for energy carriers due to their exceptional properties, including strong reducibility and high redox potential. These attributes make them well-suited for various clean energy applications, ranging from advanced batteries to electrochemical conversion processes. Until now, the practical utilization of hydride ions has been hindered by the absence of a material capable of efficiently conducting pure H- ions at ambient temperatures. To address this challenge, the DICP research team adopted a novel approach, targeting rare earth hydrides (REHx) and introducing lattice defects to enhance ion diffusion. However, the development of a superionic conductor by Chinese scientists has shattered this barrier, opening doors to a new era of clean energy innovation.
The Breakthrough Technique: The research team deliberately created nanosized grains and lattice defects in the structure of trihydrides, disrupting the path of electron transport while facilitating the movement of hydride ions. Unlike conventional methods that aim to minimize imperfections, this approach leveraged the deliberate introduction of defects to enhance ionic conductivity. Through high-energy ball milling, the team successfully suppressed electron conduction in LaHx by several orders of magnitude, transforming it into a pure hydride ion conductor with exceptional conductivity at room temperature.
By creating nano-sized grains, defects and other crystalline mismatched zones in a known ionic-electronic mixed conductor, we demonstrated that the electronic conductivity of LaHx (x ‘ 2.94) can be largely suppressed by five orders of magnitude,” said Chen. “Engineering such a material could transform LaHx into a pure hydride ion conductor with record high conductivities in the temperature range of -40℃ to 80℃.” The researchers effectively suppressed electron conduction of LaHx by decreasing the particle size and distorting the lattice via high-energy ball milling, which involves subjecting the material to high-energy collisions. With fast H− conduction and a high ion transfer number, the deformed LaHx material would enable a hydride ion battery to operate at room temperature or lower. “This work demonstrates the effectiveness of lattice deformation in suppressing electron conduction in REHx,” said Chen
The Promise of All-Solid-State Systems:
The newly engineered superionic conductor enables the seamless flow of H- ions within its structure, even under ambient conditions. This breakthrough sets the stage for the advancement of all-solid-state hydride-based batteries and fuel cells, offering numerous advantages over traditional liquid electrolyte systems. All-solid-state energy storage devices mitigate safety concerns associated with leaks and flammability, presenting a viable solution for reliable and secure energy storage. Furthermore, these systems boast higher energy density and improved performance, with the potential for faster charging and discharging times compared to their liquid electrolyte counterparts. As the world transitions towards a cleaner and more sustainable energy landscape, the development of all-solid-state hydride-based systems represents a significant step forward in achieving this vision.
While BLHO demonstrates exceptional conductivity in the intermediate temperature range, further research is needed to stabilize its performance at lower temperatures. The ultimate goal is to develop hydride ion conductors capable of operating across a broader temperature spectrum, from room temperature to intermediate temperatures. This ambitious endeavor holds the promise of revolutionizing energy storage technologies, paving the way for more efficient and sustainable energy solutions that harness the charge flexibility of hydrogen.
The Road Ahead:
Despite the remarkable progress achieved in this research endeavor, there remains a crucial need for further development and exploration. Moving forward, scientists will prioritize two critical areas of advancement:
Understanding the underlying mechanisms: Delving deeper into the intricacies of how the material enables superionic conduction is paramount. By unraveling the underlying mechanisms at play, researchers can gain valuable insights to fine-tune and optimize the performance of this groundbreaking material. This comprehensive understanding will be instrumental in unlocking its full potential and maximizing its efficiency in practical applications.
Scaling up production: While the successful synthesis of the material represents a significant breakthrough, the journey towards widespread adoption hinges on the ability to produce it on a larger scale. To realize the promise of this innovation in real-world scenarios, scientists must devise cost-effective and scalable production methods. Streamlining the manufacturing process will not only ensure the accessibility of the material but also accelerate its integration into various energy storage and conversion technologies, paving the way for a sustainable energy future.
Conclusion:
The achievement of superionic hydride ion conduction at ambient temperatures represents a significant milestone in the advancement of clean energy storage. With this breakthrough, researchers are poised to revolutionize the landscape of energy technologies, paving the way for sustainable and eco-friendly solutions to meet the world’s growing energy needs. As efforts continue to push the boundaries of innovation, the promise of efficient and accessible clean energy draws ever closer to realization.
