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 degrees C, and the nanoparticles remained amorphous after heating at 450 degrees C in H-2(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.