Pure Carbon Triggers Nitrogen Reduction: The Critical Role of Spin Electrons Induced at sp³/sp² Carbon Interfaces

Carbon-based metal-free catalysts have attracted considerable interest for the electrochemical nitrogen reduction reaction (eNRR) under ambient conditions, but their activity origin is often attributed to heteroatoms or defects, while this work demonstrates the activity of pure carbon without doping or defects. Herein, we unveil a spin mechanism induced at sp³/sp² carbon interfaces that triggers nitrogen reduction, based on a combination of grand-canonical first-principles calculations, constant-potential AIMD simulations, and rigorous experiments. With the presence of sp³/sp² carbon interfaces in our model, it emerges isolated bands adjacent to the Fermi level and extended spin distribution originating from electronic redundancy. Through a spin-mediated activation mechanism, N₂ is highly activated with chemisorption on the dual-spins of sp³/sp² carbon interfaces. Thermodynamic results show that N₂ adsorption is the single uphill step of eNRR with 1.26 eV, while the following steps proceed downhill with the spontaneous NH₃ desorption at -0.65 V vs RHE. Kinetic barriers, evaluated through constant-potential enhanced sampling, confirm the high activity under typical operating conditions (pH = 7, -0.65 V): with Li⁺, N₂ adsorption needs to overcome a kinetic barrier of 1.22 eV (further to 0.94 eV with a graphene substrate), followed by facile hydrogenation steps to form NH₃─all featuring kinetic barriers below 0.65 eV. Guided by theory, we synthesized a carbon nanosheet-nanotube composite, experimentally verified sp³/sp² carbon interfaces and spin signatures, and achieved an NH₃ yield rate of 86.3 μg·h^-1·mg^-1_cat., ranking among the best carbon-based metal-free eNRR catalysts. This work highlights the atomic-level insights and interfacial spin engineering for intrinsic reactivity in pure carbon electrocatalysts.