Fe ₂ P encapsulated in carbon nanowalls decorated with well-dispersed Fe ₃ C nanodots for efficient hydrogen evolution and oxygen reduction reactions

The development of cost-effective, high-efficiency bifunctional electrocatalysts as alternatives to the state-of-the-art Pt-based materials toward the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is of great significance but still challenging. Herein, an advanced bifunctional electrocatalyst is presented, composed of Fe₂P encapsulated in carbon nanowalls decorated with well-dispersed Fe₃C nanodots (denoted as Fe₂P@Fe₃C/CNTs), which is achieved by a novel "inside-out" gas-solid reaction protocol. When functioning as a cathodic catalyst for water splitting, the Fe₂P@Fe₃C/CNT catalyst needs an ultralow overpotential of 83 mV to deliver a current density of 10 mA cm^-2, shows a small Tafel slope of 53 mV dec^-1 and ensures long-term stability for over 200 h in an alkaline electrolyte. Notably, the Fe₂P@Fe₃C/CNT catalyst exhibits an extremely impressive ORR performance with an onset potential (E_onset) of 1.060 V and a half-wave potential (E_1/2) of 0.930 V, excellent stability (≈94% activity retention after 36 000 s), and a strong methanol resistance ability, even far outperforming commercial Pt/C (E_onset = 0.955 V, E_1/2 = 0.825 V, ≈75% activity retention after less than 3500 s). Such outstanding HER and ORR performances are mainly ascribed to the improved corrosion resistance of the unique Fe₂P@C core-shell structures, the abundant catalytically active sites of ultrasmall Fe₃C nanodots incorporated in carbon nanowalls, and the good electrical conductivity of 2D graphitic carbon nanotubes used as a support.