d-p orbital hybridization between the Ru 4d and the C≡N 2p induces π-backdonation and further modulates the d-electron structure of V/Fe, enabling the cooperative V³⁺/V⁴⁺, Ru^(2x-δ)+/Ru^2x+, and Fe²⁺/Fe³⁺ multi-redox reactions.

Abstract

Electrochemical proton storage offers grid-scale energy storage system with long lifespan, great safety, and eco-friendliness. However, preparing proton storage materials with balanced conductivity, activity, and stability remains challenging due to suboptimal structure design. Herein, we report atomic-level engineering of d-p orbital hybridization strategy to regulate transition metal (V/Fe) d-band centers. Vanadium hexacyanoferrate (VHCF)/RuO_x quantum dots (RuO_xQDs) heterostructure (VHCF–RuO_xQDs) was synthesized via in situ co-precipitation. The d-p hybridization of Ru's 4d orbital with VHCF's C≡N 2p orbital (cyano) induces π-backdonation and creates “electronic highways” for regulating the d-electrons of V/Fe, shifting their d-band centers to achieve continuous multi-electron transfer. Moreover, optimizing the d-electron structure reduces the V⁵⁺ ratio and thus decreases vanadium dissolution during cycling. The VHCF–RuO_xQDs cathode delivers a large capacity of 162 mAh g⁻¹ at 1 A g⁻¹, excellent rate capability (127 mAh g⁻¹ at 40 A g⁻¹), and ultralong stability over 10 000 cycles. When paired with MoO₃–MXene anode, the asymmetric full device achieves a high energy density of 53 Wh kg⁻¹ at 1.3 kW kg⁻¹. The atomic-level orbital hybridization regulation of d-electron structure provides a new direction for high-performance proton storage.