Fabricating hierarchical core-shell nanostructures is currently the subject of intensive research in the electrochemical field owing to the hopes it raises for making efficient electrodes for high-performance supercapacitors. Here, we develop a simple and cost-effective approach to prepare CuO@MnO₂ core-shell nanostructures without any surfactants and report their applications as electrodes for supercapacitors. An asymmetric supercapacitor with CuO@MnO₂ core-shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide (MEGO) as the negative electrode yields an energy density of 22.1 Wh kg⁻¹ and a maximum power density of 85.6 kW kg⁻¹; the device shows a long-term cycling stability which retains 101.5% of its initial capacitance even after 10000 cycles. Such a facile strategy to fabricate the hierarchical CuO@MnO₂ core-shell nanostructure with significantly improved functionalities opens up a novel avenue to design electrode materials on demand for high-performance supercapacitor applications.

Complexity in strongly correlated oxides such as perovskite strictly dominates their performance for oxygen reduction reaction (ORR). Precise control of the physical correlations among spin, charge, orbital, and lattice degrees of freedom in these oxides can exercise considerable enhancement of ORR activity, but has until now remained elusive. Here, we show that nonmagnetic hexavalent molybdenum (Mo⁶⁺) atomically dispersed within oxide lattice steers the intrinsic activity of catalytically active sites by entrapping extrinsic electrons at their 3d orbitals, without the occurrence of lattice symmetry breaking and magnetic perturbation. With double perovskite La₂Co²⁺Mn⁴⁺O₆ as a model catalyst, the atomic-scale electron trap generates additional high-spin, catalytically active Mn³⁺(t³ _2ge¹ _g) sites and highly conductive Co²⁺(e² _g)–O–Mn³⁺(e¹ _g) double exchange channels, leading to five-fold improvement in ORR activity. First-principles calculations reveal a substantial increase of the spin density on Mn sites caused by electron trapping, and unambiguously confirm a more exothermic reaction pathway as well as a lower barrier of the rate-limiting surface hydroxide regeneration on Mo₁/La₂CoMnO₆. We can also extend this strategy with atomic precision easily to other four oxide catalysts and achieve large enhancement in their ORR activities as anticipated, indicating its broad utility. This work embodies the theories of condensed matter physics in rational design of ORR catalysts, and may inspire further development of the control of electron correlation in strongly correlated electron systems.