Decoupling morphology to reveal intrinsic activity: Quantum-sized vanadium nitride for bifunctional hydrazine splitting.

The identification of intrinsic catalytic activity in electrocatalytic systems remains challenging due to the strong coupling between electronic structure and morphological effects. Here, we constructed a series of ultrafine transition metal nitride nanodots (VN/C, MoN/C, WN/C, and CoN/C) with nearly identical particle sizes and carbon supports via a unified template-assisted chemical vapor deposition strategy, thereby minimizing morphological variations and enabling direct attribution of catalytic performance to intrinsic electronic structure. Replacing the sluggish oxygen evolution reaction with the hydrazine oxidation reaction (HzOR) provides a thermodynamically favorable pathway, while imposing stringent requirements on bifunctional catalysts capable of driving both HER and HzOR. The intrinsic catalytic activities of these nitrides showed clear differentiation, and VN/C exhibited the best bifunctional performance, with overpotentials of 68/133 mV for HER and - 45/125 mV for HzOR at 10/100 mA cm. Mechanistic analysis revealed that the near-optimal d-band center of VN enabled balanced adsorption-desorption of reaction intermediates, whereas CoN and WN/MoN were limited by excessively strong and weak adsorption, respectively. This intrinsic advantage extended to the device level, where VN/C enabled low-voltage overall hydrazine splitting and achieved an energy efficiency of 97.9% with stable cycling in a Zn-hydrazine battery.