Amorphous molybdenum phosphide nanoparticles for electrocatalytic hydrogen evolution

Amorphous molybdenum phosphide (MoP) nanoparticles have been synthesized and characterized as electrocatalysts for the hydrogen-evolution reaction (HER) in 0.50 M H₂SO₄ (pH 0.3). Amorphous MoP nanoparticles (having diameters of 4.2 ± 0.5 nm) formed upon heating Mo(CO)₆ and trioctylphosphine in squalane at 320 °C, and the nanoparticles remained amorphous after heating at 450 °C in H₂(5%)/Ar(95%) to remove the surface ligands. At mass loadings of 1 mg cm^-2, MoP/Ti electrodes exhibited overpotentials of -90 and -105 mV (-110 and -140 mV without iR correction) at current densities of -10 and -20 mA cm^-2, respectively. These HER overpotentials remained nearly constant over 500 cyclic voltammetric sweeps and 18 h of galvanostatic testing, indicating stability in acidic media under operating conditions. Amorphous MoP nanoparticles are therefore among the most active known molybdenum-based HER systems and are part of a growing family of active, acid-stable, non-noble-metal HER catalysts.