A Simple and Scalable Route to Synthesize CoxCu1-xCo2O4@CoyCu1-yCo2O4 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 Co3O4@Co3O4 is prepared using a simple and scalable hydrothermal reaction, followed by a calcination process. Then, CoxCu1-xCo2O4@CoyCu1-yCo2O4 microspheres are synthesized via adsorption and calcination processes using the as-prepared Co3O4@Co3O4 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 CoxCu1-xCo2O4@CoyCu1-yCo2O4 microspheres exhibit high performance with a turnover frequency (TOF) of 81.8 mol(hydrogen) min(-1) mol(cat)(-1). This is one of the highest TOF values reported for a noble-metal-free catalyst in the literature. Additionally, the yolk-shell structured CoxCu1-xCo2O4@CoyCu1-yCo2O4 microspheres are highly stable and reusable. These yolk-shell structured CoxCu1-xCo2O4@CoyCu1-yCo2O4 microsphere is a promising catalyst candidate in AB hydrolysis considering the excellent catalytic behavior and low cost.