Full-Density TiB₂ Cathodes for Energy-Efficient Aluminum Electrolysis via Oriented Assembly in Molten Salts.

Abstract

Developing wettable titanium diboride (TiB₂) cathodes enables energy-conservation aluminum electrolysis technology with significant carbon dioxide (CO₂) emissions reduction for the sustainability of aluminum industry. However, synthesizing suitable TiB₂ cathodes remains challenging. Herein, we propose a promising strategy for <i>in situ</i> synthesis of TiB₂-coated cathodes via the oriented assembly of TiB₂ nanocrystals (NCs) in high-temperature molten salts. Colloidal TiB₂ NCs with an average size of 4.1 nm were synthesized in a molten cryolite-based bath at 1243 K. Under an electric field, they migrated to the cathode surface through oriented attachment crystallization, assembling directly into TiB₂ coatings with a thickness of up to hundreds of micrometers. These coatings exhibited fully dense structures with exceptionally low oxygen content (≤90 ppm). The <i>in situ</i> assembled TiB₂-coated cathodes demonstrated an extremely low wear rate of 0.09 mm yr^-1 during aluminum electrolysis. This technique potentially enables significant reductions in electricity consumption and corresponding CO₂-equivalent emissions. Implementation of these TiB₂ cathodes for retrofitting existing electrolytic cells, or combining them with inert anodes for carbon-free aluminum electrolysis, represents a viable pathway. Our work resolves the fundamental conflict between aluminum's essential role in the energy transition and the aluminum electrolysis industry's high energy consumption and emissions. It demonstrates the groundbreaking application of oriented assembly technology within high-temperature molten salt systems, addressing critical materials preparation challenges in traditional metallurgical processes.