Rational Design of Earth-Abundant Phosphide Electrocatalysts

Metal phosphide nanoparticles have been shown to be promising electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). We performed systematic studies of the polycrystalline and facet-selective single crystal of 3d transition metal phosphide electrocatalysts. In-situ studies at SLAC SSRL show that P in phosphide plays an important role in H adsorption. At HER applied bias the surface of the catalysts is reduced, and oxidation of the surface occurs only after the reducing bias is turned off, explaining common ex-situ observation of oxidized surface of the used catalysts. Studies of <i>M</i>₂P (<i>M</i> = Fe, Co, Ni) single crystals show that crystal facets have drastically different reactivity thus paving the way to enhance activity of nanocrystalline catalysts via shape control. Finally, tuning of electronic structure and chemical bonding between <i>M</i> and P sublattices via aliovalent substitution allow to enhance activity and stability of ternary ordered phosphide electrocatalysts.