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

Abstract 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/FeNi 2 P 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, FeNi 2 P, 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 ( E 1/2 = 0.83 V), HzOR ( E 100 = 7 mV), and HER ( E 100 = ‐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.