Porous Nitrogen Self‐Doped Carbon Wrapped Iron Phosphide Hollow Spheres as Efficient Bifunctional Electrocatalysts for Water Splitting

In this work, a series of hybrid materials of N‐self‐doped carbon wrapped Fe 2 P/FeP hollow spheres were prepared by using a two‐step thermal conversion of precursors derived from the in situ coating of polyaniline on commercial Prussian blue. The precursors were pyrolyzed in N 2 to form the N‐doped carbon coating on carbon‐iron materials; this was followed by subsequent phosphorization using NaH 2 PO 2 as a phosphorus source, yielding the hybrid materials of N‐doped carbon wrapped Fe 2 P/FeP hollow spheres. The resulting hybrid materials showed high Brunauer‐Emmett‐Teller surface areas, pore volumes, and nitrogen contents, which were, more than 80 % pyridinic‐N. The hybrid materials were evaluated as electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH, and they have exhibited excellent electrocatalytic activities in the two reactions. In the case of the optimum sample, the 0.75‐NC−Fe x P catalyst, a low overpotential/Tafel slope of 193 mV/58 mV ⋅ dec −1 for HER and 302 mV/42 mV ⋅ dec −1 for OER were obtained. More importantly, the catalyst showed high catalytic activity for overall water splitting and only 1.63 V of cell voltage was needed to reach 10 mA/cm 2 in a two‐electrode electrolyzer. The catalyst also exhibited robust long‐term durability and only a 16.0 % decrease in current density was observed after a 10 h chronoamperometric testing at 1.63 V. The results suggest that the sample is a promising alternative non‐precious‐metal catalyst for overall water splitting.