Fe2P encapsulated in carbon nanowalls decorated with well-dispersed Fe3C 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 (Eonset) of 1.060 V and a half-wave potential (E1/2) 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 (Eonset = 0.955 V, E1/2 = 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.