Visualizing orbital-level d-band modulation in RuCoN nanoalloys anchored on N-doped carbon nanotubes for efficient alkaline AEM water electrolysis

Despite extensive theoretical studies on d-band engineering, the lack of direct experimental evidence at the orbital level continues to hinder the rational design of efficient electrocatalysts for the alkaline hydrogen evolution reaction (HER), particularly in anion-exchange membrane water electrolyzers (AEMWEs). Herein, we report a RuCoN alloy anchored on nitrogen-doped carbon nanotubes (RuCoN-NCNT) that achieves outstanding HER performance, delivering an ultralow overpotential of 13 mV at 10 mA·cm⁻² and long-term durability exceeding 60 h at 100 mA·cm⁻². To unravel the intrinsic electronic structure–activity relationships, we employ advanced spectroscopic techniques, including in-situ Raman and rarely utilized inverse photoemission/ultraviolet photoelectron spectroscopy (IPES/UPS). The orbital-resolved measurements reveal that pyridinic-N mainly converts to RuCoN, which reinforces the structural robustness by enhancing electronic coupling, and pyrrolic-N and metal-N pull the d-band center upward and broaden the conduction band, optimizing H*/H₂O adsorption and conversion. These together enable optimized electron distribution for high catalytic activity. The synergy between nitrogen configurations and the RuCoN alloy creates electronically integrated catalytic sites with optimized charge distribution. When assembled in a full AEMWE device, the optimal RuCoN-NCNT-400 catalyst surpasses commercial Pt/C, demonstrating industrial-level activity and long-term stability. This work provides direct experimental validation of d-band modulation, establishing a framework for orbital-level catalyst engineering and bridging the gap between theoretical predictions and practical HER electrocatalysis.