Electrocatalytic and Magnetic Properties of Porous Iron Phosphide Nanorods

Nanoscale transition metal phosphide systems hold significant technological potential due to their distinctive optoelectronic properties, high catalytic activity, superparamagnetism, and high diffusion coefficient of Na/Li ions. However, attempts to synthesize phase-pure FeP, a promising electrocatalyst, have utilized expensive and/or highly reactive phosphide precursors such as tri-<i>n</i>-octylphosphine (TOP), white phosphorus (P₄), tris-(trimethylsilyl)-phosphine (P-(TMS)₃), and tri-<i>n</i>-butylphosphine. These methods often require high temperatures and/or multistep reaction processes. Here, to address these limitations, we present a solution-based synthesis method to produce phase-pure FeP nanoparticles. In this synthesis, we react iron oxyhydroxide (β-FeOOH) as a cost-effective, environmentally friendly, and air-stable source of iron with tris-diethylaminophosphine P-(NEt₂)₃ as a phosphorus source at 280 °C. The resulting FeP is formed in a porous nanorod morphology. The particles were characterized by TEM and XPS. Magnetic measurements of the phase-pure FeP nanoparticles indicate paramagnetic behavior, contrasting the antiferromagnetic behavior observed in bulk FeP. In addition to their unique magnetic properties, these porous FeP nanorods demonstrate promising HER performance, achieving an overpotential of 267 mV at a geometric current density of -10 mA cm^-2 in acidic media, with stable electrocatalytic activity maintained for up to 12 h at -50 mA cm^-2. This study represents the first documented low-temperature, time-efficient, solution-based thermal decomposition method for synthesizing phase-pure FeP nanoparticles, using tris-(diethylamino)-phosphine P-(NEt₂)₃ and iron oxyhydroxide (β-FeOOH) as sources of phosphorus and iron, respectively, at 280 °C.