Constructing Three‐Phase Heterojunction with 1D/3D Hierarchical Structure as Efficient Trifunctional Electrocatalyst in Alkaline Seawater

Rational design of highly efficient, robust, and low‐cost trifunctional electrocatalysts for oxygen reduction reaction (ORR), hydrazine oxidation reaction (HzOR), and hydrogen evolution reaction (HER) is extremely urgent for seawater‐based renewable energy conversion and storage, including direct hydrazine fuel cells (DHzFC) and overall hydrazine splitting (OHzS). Herein, FeP/FeNi2P encapsulated in N, P co‐doped hierarchical carbon (FeNiP‐NPHC) in situ grown on nickel foam is fabricated via a hydrothermal‐pyrolysis‐phosphidation procedure. Benefiting from the strong coupling effect among FeP, FeNi2P, and N, P co‐doped carbon at the three‐phase heterojunction interface, as well as the unique 1D/3D hierarchical structure, the as‐prepared FeNiP‐NPHC shows superior ORR (E1/2 = 0.83 V), HzOR (E100 = 7 mV), and HER (E100 = ‐180 mV) performance in alkaline seawater. Density functional theory functions indicate that constructing three‐phase heterojunction interface of FeNiP‐NPHC can effectively adjust the d‐band center and electronic structure, which is conductive to balance and optimize the trifunctional electrocatalytic performance. As proof of concept, the self‐assembled DHzFC is utilized to power the OHzS in alkaline seawater successfully, verifying application potential of the FeNiP‐NPHC as trifunctional electrocatalyst. The first synthesized FeP/FeNi2P encapsulated in N, P co‐doped hierarchical carbon (FeNiP‐NPHC) in‐situ grown on nickel foam. Benefiting from the synergistic effect of strongly‐coupled three‐phase heterojunction interface and 1D/3D hierarchical structure, the FeNiP‐NPHC hybrid displays excellent performance for hydrazine oxidation reaction, hydrogen evolution reaction, and oxygen reduction reaction in the alkaline seawater system.