Hierarchically porous electrodes made of electrochemically active materials and conductive additives may display synergistic effects originating from the interactions between the constituent phases, and this approach has been adopted for optimizing the performances of many electrode materials. Here we report our findings in design, fabrication, and characterization of a hierarchically porous hybrid electrode composed of α-NiS nanorods decorated on reduced graphene oxide (rGO) (denoted as R-NiS/rGO), derived from water-refluxed metal–organic frameworks/rGO (Ni-MOF-74/rGO) templates. Microanalyses reveal that the as-synthesized α-NiS nanorods have abundant (101) and (110) surfaces on the edges, which exhibit a strong affinity for OH⁻ in KOH electrolyte, as confirmed by density functional theory-based calculations. The results suggest that the MOF-derived α-NiS nanorods with highly exposed active surfaces are favorable for fast redox reactions in a basic electrolyte. Besides, the presence of rGO in the hybrid electrode greatly enhances the electronic conductivity, providing efficient current collection for fast energy storage. Indeed, when tested in a supercapacitor with a three-electrode configuration in 2 M KOH electrolyte, the R-NiS/rGO hybrid electrode exhibits a capacity of 744 C g⁻¹ at 1 A g⁻¹ and 600 C g⁻¹ at 50 A g⁻¹, indicating remarkable rate performance, while maintaining more than 89% of the initial capacity after 20 000 cycles. Moreover, when coupled with a nitrogen-doped graphene aerogel (C/NG-A) negative electrode, the hybrid supercapacitor (R-NiS/rGO/electrolyte/C/NG-A) achieved an ultra-high energy density of 93 W h kg⁻¹ at a power density of 962 W kg⁻¹, while still retaining an energy density of 54 W h kg⁻¹ at an elevated working power of 46 034 W kg⁻¹.

We report a hollow carbon nanopolyhedron catalyst doped with N and single Fe atoms, prepared by pyrolyzing hollow ZIF-8 with ferric acetylacetonate and g-C₃N₄. The catalyst retains the polyhedral morphology of its precursor and possesses exclusively Fe–N₄ moieties promoted by g-C₃N₄ nitriding, evidenced by multipronged microscopic and spectroscopic analyses. In rotating disk measurements, the catalyst exhibits superior ORR activity in both acidic and alkaline media, with a half-wave potential of 0.78 V in the former and 0.845 V in the latter. In addition, its ORR stability surpasses that of commercial Pt/C in acidic and alkaline media. Most notably, the catalyst exhibits ultra-high performance in a H₂/O₂ proton exchange membrane fuel cell (PEMFC), with a current density of 400 mA cm⁻² at 0.7 V and 133 mA cm⁻² at 0.8 V, and a maximum power density of 628 mW cm⁻². This is among the best PEMFC performances reported for cathodes free of platinum-group metals. We attribute this excellent-ORR activity to the integration of the high density Fe(II)–N₄–H₂O moiety (4.51956 × 10¹³ sites cm⁻²) embedded in the carbon framework, identified by in situ X-ray absorption spectroscopy, and the well-balanced micro/meso/macroporous structure.