Hierarchical porous carbon nanofibers embedded with one-dimensional conjugated metal−organic framework anodes for ammonium-ion hybrid supercapacitors

Ammonium-ion (NH4+) hybrid supercapacitors are promising energy storage devices due to their low cost, high energy/power supply, and environmental friendliness. However, it remains a grand challenge to engineer electrode materials toward high-efficient NH4+ storage. Herein, we report 1D conjugated metal−organic frameworks (1D c-MOFs) grown on hierarchical porous carbon nanofibers (HPCNFs), representing an attractive NH4+ host material that enables fast diffusion kinetics. Featuring high electrical conductivity, hierarchical porous structure, and dense active sites, the HPCNFs embedded with Ni-BTA (BTA = 1,2,4,5-benzenetetramine) c-MOF composite (denoted as HPCNFs@Ni-BTA) delivers an ultrahigh specific capacitance of 678.5 F g−1 at 0.5 A g−1 and an outstanding rate capability (220.1 F g−1 at 10 A g−1). Experimental analyses and theoretical calculations confirm that, strong NH4+ adsorption capability comes from the reversible redox reaction occurred at NiN4 linkages between the C=N and C−N bonds. By coupling HPCNFs@Ni-BTA anode with HPCNFs cathode, the NH4+ full device outputs a high specific capacitance of 156 F g−1 at 0.3 A g−1 and a remarkable energy density of 48.8 Wh kg−1, outperforming most recently reported aqueous supercapacitors. This work provides an exciting strategy for designing advanced functional electrodes for the next-generation energy applications.