Iron–nitrogen–carbon single-atom catalysts (Fe–N–C SACs) are widely acknowledged for their effective oxygen reduction activity, however, their activity requires further enhancement. Meanwhile, additional structural optimization is necessary to enhance mass transport and achieve higher power density in practical applications. Herein, using ZIF-8 as a template, we synthesized yolk–shell catalysts featuring complex sites of Fe single atoms and Cu nanoclusters (y-FeCu/NC) via partial etching and liquid-phase loading. The synthesized y-FeCu/NC catalyst exhibits high specific surface area and mesoporous volume. Combined with the advantages of highly active sites and yolk–shell structure, the y-FeCu/NC catalyst demonstrated outstanding catalytic performance in the oxygen reduction reaction, achieving a half-wave potential (E_1/2) of 0.97 V in 0.1 M KOH. As a practical energy device, Zn-air battery (ZAB) assembled with y-FeCu/NC catalyst achieved a remarkable power density of 356.3 mW·cm^–2, representing an improvement of approximately 28.5% compared to its solid FeCu/NC counterpart. Furthermore, it showcased impressive stability, surpassing all control samples.

The actual manufacture of supercapacitors (SCs) is restricted by the inadequate energy density, and the energy density of devices can be properly promoted by assembling zinc-ion capacitors (ZICs) which used capacitive cathode and battery-type anode. Two-dimensional (2D) MXene has brought great focuses in the electrode research on the foundation of large redox-active surface, but the specific capacitance is still affected by the tight stacking of interlaminations. Ti₃C₂T_x@polyaniline (PANI) heterostructures are prepared by uniformly depositing the conductive polymer PANI nanorods as the intercalation agent into the external of Ti₃C₂T_x nanosheets to inhibit stacking. Subsequently, by using graphene oxide (GO)-assisted low-temperature hydrothermal self-assembly manufacture, 2D heterostructures are assembled into the three-dimensional (3D) porous crosslinked Ti₃C₂T_x@PANI-reduced graphene oxide (RGO) hydrogels. Attributed to the synergistic work of PANI nanorods, Ti₃C₂T_X nanosheets, and 3D crosslinking frameworks of RGO to match capacitive and battery effects, 3D porous hierarchical Ti₃C₂T_x@PANI-RGO heterostructure hydrogels have rich ion transport channels, a large number of active sites, and excellent reaction kinetics. ZIC is assembled by using Ti₃C₂T_x@PANI-RGO heterostructure hydrogels as cathodes and zinc foil as anodes. In this work, Ti₃C₂T_x@PANI-RGO//Zn ZIC exhibits a wide working window (2.0 V), marked specific capacitance (589.89 F·g⁻¹ at 0.5 A·g⁻¹), salient energy density (327.71 Wh·kg⁻¹ at 513.61 W·kg⁻¹ and 192.20 Wh·kg⁻¹ at 13,005.87 W·kg⁻¹), and durable cycling stability (97.87% capacitance retention after 10,000 cycles at 10 A·g⁻¹). This study emphasizes the device design of ZICs and the broad prospect of Ti₃C₂T_x-based hydrogels as viable cathodes for ZICs.