Exceptional intrinsic bifunctional performance of Fe2N–Fe3C heterostructure and STH efficiency†

Developing cost-effective, efficient bifunctional electrocatalysts is crucial for large-scale H₂ production through electrochemical water splitting. Herein, we established a dual effect synthetic strategy to construct an Fe₂N–Fe₃C heterostructure as a highly active bifunctional electrocatalyst, derived from egg as the N/C-source and FeCl₃ as the iron source. The fabricated Fe₂N–Fe₃C heterostructure required overpotentials of ±151 and ±251 mV for the HER and OER, respectively. The heterostructured Fe₂N–Fe₃C nanosphere worked as a bifunctional active site for water dissociation and the adsorption/desorption of intermediates, while Fe₂N transferred electrons between the active sites and the NF current collector through Fe₂N–Fe₃C bonds. The improved OER activity was further confirmed by Bode analysis at various potentials. Temperature-dependent analysis revealed that 8HFe₂N–Fe₃C showed decreased activation energy (3.65 kJ mol⁻¹) compared with 7HFe₂N–Fe₃C (6.51 kJ mol⁻¹) and 9HFe₂N–Fe₃C (10.46 kJ mol⁻¹). The effect of phosphate anions on the OER activity of 8HFe₂N–Fe₃C/NF was analysed by changing the electrolyte from 1 M KOH to a mixture of 1 M KOH and 1 M NaH₂PO₄. Further, an electrolyzer with an Fe₂N–Fe₃C^(+,−) electrode required an ultralow 1.56 V to reach 10 mA cm⁻² for rapid H₂ generation with 100% faradaic efficiency, exceeding that of the Pt/IrO₂ couple. The Fe₂N–Fe₃C heterostructure maintained stability over 50 h for the HER, OER and overall water splitting. Renewable energy derived H₂ generation was established using a solar-assisted electrolyzer at 1.56 V, suggesting the capability of utilizing the full biomass material using the dual effect strategy for efficient energy conversion.