Is nickel phosphide an efficient catalyst for the oxygen-evolution reaction at low overpotentials?

Abstract

Recently, metal phosphides have been reported as a new class of oxygen-evolving (pre)catalysts with superior electrochemical activity. Herein, the oxygen-evolution reaction in the presence of Ni₂P was investigated, using scanning electron microscopy, nuclear magnetic resonance spectroscopy, transmission electron microscopy, spectroelectrochemistry, energy dispersive spectrometry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electrochemical methods. Under the oxygen-evolution reaction (OER), Ni₂P was converted to nickel (hydr)oxide, which is an efficient catalyst for the OER only in the presence of Fe ions. The addition of Fe salt is a method proposed for detecting the conversion of Ni₂P to Ni (hydr)oxide under the OER at low overpotentials. The different electrochemical methods showed that the thin and amorphous layer of Ni (hydr)oxide coupled with the high conductivity of Ni₂P made core (Ni₂P)–shell (Ni (hydr)oxide, 0.5–5 nm) type nanoparticles excellent substrates for adsorbing Fe ions and formed an excellent oxygen-evolving compound. The overpotential of the onset for the oxygen-evolution reaction in the presence of these nanoparticles was 217 mV in KOH (0.10 M).