A Facile Magnetically-Confined Plasma Strategy for Distinct Phase Modulation of Iron Nitride Nano-Frameworks

Distinct material phase modulation is widely regarded as a key strategy for tailoring the surface properties of nano-frameworks. Plasma has emerged as an effective method for in situ phase modulation directly on substrate surfaces. However, the persistent vertical bombardment of reactive species in a conventional plasma system inevitably leads to excessive surface etching, thereby compromising the distinction and quality of surface structural engineering. Herein, we introduce a novel magnetically confined plasma strategy that enables the unique phase modulation of iron nitride nano-frameworks on iron substrates. By varying the magnetic field strength, the resultant iron nitride phase transitions from orthorhombic Fe₂N to trigonal Fe₂N, with a well-defined exposed facet, is achieved. In contrast, the conventional plasma nitridation predominantly yields hexagonal FeN. Operando plasma diagnostics and numerical simulations are employed to elucidate the underlying mechanism governing phase modulation. The superior distinction of phase modulation via magnetically confined plasma processing is further validated by comparing with conventional plasma nitridation under varying discharge parameters. Such apparent structural differences of nitrides via magnetically-confined plasma are confirmed through the corresponding electrocatalytic performance evaluation and theoretical calculations. Such an approach offers a promising pathway for the distinct structural engineering of nitrides directly on the substrate surface toward improved electrocatalytic behavior.