Phase-engineered metal boride nanobeads for highly efficient oxygen evolution

Abstract

Non-precious metals with tailored phase structures show promise as oxygen evolution reaction (OER) catalysts due to their high inherent catalytic activity and extensive exposed active surface area. However, the mechanisms by which phase structures enhance catalytic performance remain unclear. Herein, we synthesized an amorphous cobalt boride (CoB) catalyst via a magnetic field-assisted method, yielding uniform nanoparticles that self-assemble into a nanobead structure. This material undergoes heat treatment to transition from an amorphous phase to a crystalline phase. The catalyst demonstrated exceptional OER activity and long-term stability in an alkaline electrolyte, requiring only 350 mV overpotential at 10 mA cm⁻². The amorphous CoB demonstrates remarkable durability by maintaining stable operation for 100 h under harsh conditions characterized by high alkalinity and elevated temperature without any observable performance degradation. We demonstrate that electrochemical activation of an amorphous catalyst can unveil active sites within the bulk material, leveraging the short-range order characteristic of amorphous structures. This process significantly amplifies the active site density, consequently enhancing the electrocatalytic performance of the amorphous catalyst in the oxygen evolution reaction within water oxidation. Furthermore, in situ Raman spectroscopy reveals that amorphous CoB rapid self-reconstruction upon electrochemical activation, leading to the formation of a metal (oxy)hydroxide active layer. This study offers valuable insights into the design of high-efficiency OER catalysts by elucidating the mechanisms underlying amorphous and crystalline materials.