Is Nickel Phosphide an Efficient Catalyst for Oxygen-Evolution Reaction at Low Overpotentials?
Recently, metal phosphides have been reported as a new class of oxygen-evolving (pre)catalysts with superior electrochemical activity. Herein, oxygen-evolution reaction in the presence of Ni2P was investigated, using scanning electron microscopy, nuclear magnetic resonance spectroscopy, spectroelectrochemistry, transmission electron microscopy, spectroelectrochemistry, energy dispersive spectrometry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electrochemical methods. Under oxygen-evolution reaction (OER), Ni2P was converted to nickel (hydr)oxide, which is an efficient catalyst for 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 OER at low overpotentials. The different electrochemical methods showed that the thin and amorphous layer of Ni (hydr)oxide coupled with 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 oxygen-evolution reaction in the presence of these nanoparticles was 217 mV in KOH (0.10 M).