A Simple and Scalable Route to Synthesize Cox Cu1- x Co2 O4 @Coy Cu1- y Co2 O4 Yolk-Shell Microspheres, A High-Performance Catalyst to Hydrolyze Ammonia Borane for Hydrogen Production.

Yolk-shell structured micro/nano-sized materials have broad and important applications in different areas due to their unique spatial configurations. In this study, yolk-shell structured Co3 O4 @Co3 O4 is prepared using a simple and scalable hydrothermal reaction, followed by a calcination process. Then, Cox Cu1- x Co2 O4 @Coy Cu1- y Co2 O4 microspheres are synthesized via adsorption and calcination processes using the as-prepared Co3 O4 @Co3 O4 as the precursor. A possible formation mechanism of the yolk-shell structures is proposed based on the characterization results, which is different from those of yolk-shell structures in previous study. For the first time, the catalytic activity of yolk-shell structured catalysts in ammonia borane (AB) hydrolysis is studied. It is discovered that the yolk-shell structured Cox Cu1- x Co2 O4 @Coy Cu1- y Co2 O4 microspheres exhibit high performance with a turnover frequency (TOF) of 81.8 molhydrogen min-1 molcat -1 . This is one of the highest TOF values reported for a noble-metal-free catalyst in the literature. Additionally, the yolk-shell structured Cox Cu1- x Co2 O4 @Coy Cu1- y Co2 O4 microspheres are highly stable and reusable. These yolk-shell structured Cox Cu1- x Co2 O4 @Coy Cu1- y Co2 O4 microsphere is a promising catalyst candidate in AB hydrolysis considering the excellent catalytic behavior and low cost.