High-Efficient, Stable Electrocatalytic Hydrogen Evolution in Acid Media by Amorphous Fe_x P Coating Fe₂ N Supported...

Development of efficient and durable non-Pt catalysts for hydrogen evolution reaction (HER) in acid media is highly desirable. Iron nitride has emerged as a promising catalyst for its cost-effective nature, but the corresponding acidic stability must be promoted. Herein, phosphorus-decorated Fe₂ N and reduced graphene oxide (P-Fe₂ N/rGO) composite are designed and synthesized. X-ray photoelectron spectroscopy and X-ray absorption fine structure (XAFS) show that a thin layer amorphous iron phosphide is coated on the surface of Fe₂ N nanoparticles, which could be responsible for the well resistance of chemical corrosion in acidic media. Meanwhile, the P-decoration could tune the electronic state and coordination environment of iron atom as evidenced by XAFS, resulting in dramatically enhanced electrocatalytic activity of P-Fe₂ N/rGO. Density functional theory calculations reveal that both the P-connected N atoms and the Fe atoms in P-Fe₂ N/rGO catalyst are the main active sites for H* adsorption. The hydrogen-binding free energy |ΔG_H* | value is close to zero for P-Fe₂ N/rGO, suggesting a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, P-Fe₂ N/rGO catalyst could achieve a low η_onset of 22.4 mV, a small Tafel plot of 48.7 mV dec^-1 , and remarkable stability for HER in acid electrolyte.