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

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Identifying intrinsic catalytic activity in electrocatalysis is difficult due to coupled electronic and morphological effects.
• Transition metal nitrides are promising electrocatalysts but require disentangling structure-activity relationships.

Purpose of the Study:

• To construct ultrafine transition metal nitride nanodots with controlled sizes and supports to isolate intrinsic electronic structure effects.
• To evaluate the bifunctional catalytic performance of these nitrides for the hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER).

Main Methods:

• A unified template-assisted chemical vapor deposition strategy was used to synthesize ultrafine transition metal nitride nanodots (VN/C, Mo2N/C, W2N/C, CoN/C) on carbon supports.
• Electrochemical techniques were employed to assess the catalytic activities for HER and HzOR.
• Mechanistic studies, including d-band center analysis, were performed to understand structure-activity relationships.

Main Results:

• VN/C exhibited the best bifunctional performance, with low overpotentials for both HER (68/133 mV at 10/100 mA cm⁻²) and HzOR (-45/125 mV at 10/100 mA cm⁻²).
• Mechanistic analysis indicated that VN/C's near-optimal d-band center facilitated balanced adsorption of reaction intermediates.
• VN/C enabled efficient overall hydrazine splitting in a Zn-hydrazine battery with 97.9% energy efficiency.

Conclusions:

• Intrinsic electronic structure, specifically the d-band center, is crucial for tuning the catalytic activity of transition metal nitrides.
• VN/C demonstrates significant potential as a bifunctional catalyst for energy conversion applications, such as hydrazine splitting.