Unlocking the Potential of Metal Borides Nanocrystals—A Journey Through Synthesis and Surface Modification

Metal borides, a versatile class of materials used in various industrial applications such as superconductors, magnetic materials, and hot cathodes, remain under-explored at the nanoscale due to the challenges in synthesizing single-phase nanocrystals (NCs). Their small size, high surface area-to-volume ratio, and well-defined surfaces exhibit unique physical and chemical properties, making them appealing for various applications, including catalysis, energy storage, electronics, and biomedical imaging. While metal-rich borides, like Ni₃B, are mainly used in electrocatalysis, boron-rich metal borides (metal hexaborides, MB₆) are highly valued for their broad range of physical properties that vary based on the metal ion present in their structure. For example, CeB₆ and LaB₆ have low work functions, while CaB₆ and SrB₆ exhibit high potential for high-temperature thermoelectric applications. Additionally, they are known for their high hardness, making them suitable for ultra-hard protective coatings.<br/> <br/>In this presentation, we will showcase a novel method for synthesizing boron-rich M₁B₆ (M₁=Sr, Ca, Ba, La, Ce) and metal-rich M_2xB (M₂=Ni, Co, Fe, x=2,3) [1] NCs through solid-state synthesis at low temperatures (380-440°C), as well as a strategy for stabilizing these crystals for use in solution-based mass production processes. Our discussion will highlight the reaction mechanisms in both classes of nanomaterials, demonstrating the versatility of boron chemistry. By using specific surface modifications, including inorganic and organic ligands, we have achieved stable suspensions of these nanocrystals in both polar and non-polar solvents, with the potential for implementation in cutting-edge technologies.<br/><br/>1. HongJ., Mutalik S., Miola M, Gerlach D., Mehrabi K. R., Ahmadi M., J. Kooi B., Portale G., Rudolf P., P. Pescarmona P., Protesescu L.,Chemistry of Materials, 2023.