Titanium Nitride Hollow Spheres Consisting of TiN Nanosheets and Their Controllable Carbon–Nitrogen Active Sites as Efficient Electrocatalyst for Oxygen Reduction Reaction

Titanium nitride hollow spheres (TiN HSs) consisting of TiN nanosheets have been developed with a carbon-template-assisted strategy. The residual carbon is activated during the removal of the carbon template by calcining at high temperature in the air, and is beneficial for the formation of more carbon–nitrogen active sites. The TiN HSs prepared exhibits a porous and uniform shell with the thickness of ∼30 nm with superior catalytic activity for the oxygen reduction reaction (ORR). The TiN HSs calcined at 325 °C (TiN HSs-325) show the more positive onset potential (0.85 V vs RHE) for ORR and the enhanced limiting current density of up to 4.5 mA cm^–2 due to its advantages of unique nanostructure and the controllable active sites. This work provides a promising approach for the design and synthesis of hollow transition metal nitrides with significantly enhanced performances for ORR and other electrochemical energy conversion/storage devices.