Boron Compounds as Stabilizers of a Complex Microstructure in a Co‐B‐based Catalyst for NaBH4 Hydrolysis

Co⋅B‐based materials are widely used as catalysts for hydrogen generation through sodium borohydride self‐decomposition. In the mid 1990 s, the aqueous and organic chemistry involved in Co⋅B synthesis and handling was studied. Nevertheless, the exact microstructure of these catalysts has remained unsolved. Herein we present an exhaustive study which shows a new and complete microstructural view of a Co⋅B‐based material together with the chemistry of the cobalt and boron involved. By using nanoscale‐resolution microscopy and spectroscopy techniques, we have elucidated the role of boron compounds as stabilizers in a complex microstructure, which also explains its high catalytic performance and long‐term stability. The catalyst is proposed to be made up of 1–3 nm hcp Co0 nanoparticles embedded in amorphous CoxB (x=1, 2, 3), CoxOy, Co(BO2)2, and B2O3 phases alternatively or all together. All of these amorphous phases protect the nanocrystalline metallic core from growth and oxidation.