Efficient nitrate and oxygen electroreduction over pyrolysis-free mesoporous covalent Co-salophen coordination frameworks on carbon nanotubes

Abstract

Co-salophen-enriched covalent organic frameworks (COFs) coating on carbon nanotube (CNT) wires were prepared with 1,3,5-triformylphloroglucinol and diaminobenzidine by one-step Schiff-base type condensation reaction. The prepared Co-salophen COF@CNTs exhibited the large-pore mesoporous (40–60 nm) nanostructures with cotton-like morphology, and high-density Co-salophen units were uniformly implanted on this easily accessible framework. This pyrolysis-free Co-salophen coordination polymers on CNTs demonstrated the outstanding oxygen reduction reaction (ORR) performance comparable to commercial Pt/C and the best Co-based catalysts, with a positive half-wave potential (E1/2) of 0.89 V (vs RHE) in 0.1 M KOH in half-cells and the maximum powder density of 156 mW cm−2 in rechargeable Zn–air battery. In particular, Co-salophen COF was firstly found to show the efficient electrocatalytic performance for reducing NO3−-N to harmless N2N (NO3−-RR). The NO3−-N conversion yield reached 87% within 12 h in neutral solution, with a N2N selectivity of 97%. This work paved a facile synthesis route for pyrolysis-free and efficient bifunctional electrocatalysts toward ORR and NO3−-RR.