N-doped carbon nanotubes encapsulated with FeNi nanoparticles derived from defect-rich, molecule-doped 3D g-C3N4 as an efficient bifunctional electrocatalyst for rechargeable zinc–air batteries

Abstract

The lack of satisfactory bifunctional oxygen catalysts has been a major obstacle for the commercialization of zinc–air batteries (ZABs). Herein, unique N-doped carbon nanotubes encapsulated with FeNi nanoparticles (FeNi/N-CNT) derived from defect-rich, molecule-doped 3D g-C₃N₄ are reported as effective bifunctional catalysts for high efficiency ZABs. FeNi/N-CNT is produced via thermal polycondensation of malazide and melamine, followed by the coordination of Fe- and Ni-containing precursors and subsequent pyrolysis. The as-synthesized FeNi/N-CNT exhibits excellent bifunctional oxygen reduction and evolution activity and stability. A primary ZAB assembled with FeNi/N-CNT presented a high peak power density and large specific capacity. Prominently, a rechargeable ZAB based on FeNi/N-CNT delivers outstanding stability in a charging/discharging cycle test (over 800 h at 5 mA cm⁻²), which places it at the forefront of various reported ZABs. Moreover, density functional theory (DFT) calculations reveal that the synergistic coupling between FeNi nanoparticles and N doped CNTs facilitated the production of a satisfactory surface electronic environment, thus enhancing the bifunctional ORR/OER performance.