Ultrasound-Triggered Assembly of Covalent Triazine Framework for Synthesizing Heteroatom-Doped Carbon Nanoflowers Boosting Metal-Free Bifunctional Electrocatalysis

The construction of multiple heteroatom-doped porous carbon with unique nanoarchitectures and abundant heteroatom active sites is promising for reversible oxygen-involving electrocatalysis. However, most of the synthetic methods required the use of templates to construct precisely designed nanostructured carbon. Herein, we introduced an ultrasound-triggered route for the synthesis of a piperazine-containing covalent triazine framework (P-CTF). The ultrasonic energy triggered both the polycondensation of monomers and the assembly into a nanoflower-shaped morphology without utilizing any templates. Subsequent carbonization of P-CTF led to the formation of nitrogen, phosphorus, and fluorine tri-doped porous carbon (NPF@CNFs) with a well-maintained nanoflower morphology. The resultant NPF@CNFs showed high electrocatalytic activity and stability toward bifunctional electrolysis, which was better than the commercial Pt/C and IrO2 electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. As a further demonstration, employing NPF@CNFs as air electrode materials resulted in an excellent performance of liquid-state and solid-state Zn-air batteries, showing great potentials of the obtained multiple heteroatom-doped porous carbon electrocatalysts for wearable electronics.