Phase-Modulation of Iron/Nickel Phosphides Nanocrystals “Armored” with Porous P-Doped Carbon and Anchored on P-Doped Graphene Nanohybrids for Enhanced Overall Water Splitting

Transition metal phosphides (TMPs) nanostructures have emerged as important electroactive materials for energy storage and conversion. Nonetheless, the phase modulation of iron/nickel phosphides nanocrystals or related nanohybrids remains challenging, and their electrocatalytic overall water splitting (OWS) performances are not fully investigated. Here, the phase-controlled synthesis of iron/nickel phosphides nanocrystals “armored” with porous P-doped carbon (PC) and anchored on P-doped graphene (PG) nanohybrids, including FeP–Fe₂P@PC/PG, FeP–(Ni_xFe_1-x)₂P@PC/PG, (Ni_xFe_1-x)₂P@PC/PG, and Ni₂P@PC/PG, are realized by thermal conversion of predesigned supramolecular gels under Ar/H₂ atmosphere and tuning Fe/Ni ratio in gel precursors. Thanks to phase-modulation-induced increase of available catalytic active sites and optimization of surface/interface electronic structures, the resultant pure-phase (Ni_xFe_1-x)₂P@PC/PG exhibits the highest electrocatalytic activity for both hydrogen and oxygen evolution in alkaline media. Remarkably, using it as a bifunctional catalyst, the fabricated (Ni_xFe_1-x)₂P@PC/PG||(Ni_xFe_1-x)₂P@PC/PG electrolyzer needs exceptional low cell voltage (1.45 V) to reach 10 mA cm⁻² water-splitting current, outperforming its mixed phase and monometallic phosphides counterparts and recently reported bifunctional catalysts based devices, and Pt/C||IrO₂ electrolyzer. Also, such (Ni_xFe_1-x)₂P@PC/PG||(Ni_xFe_1-x)₂P@PC/PG device manifests outstanding durability for OWS. This work may shed light on optimizing TMPs nanostructures by combining phase-modulation and heteroatoms-doped carbon double-confinement strategies, and accelerate their applications in OWS or other renewable energy options.