Ni/Fe Ratio Dependence of Catalytic Activity in Monodisperse Ternary Nickel Iron Phosphide for Efficient Water Oxidation

Abstract

Electrochemical water splitting is an effective way to obtain hydrogen fuel as a clean and renewable energy source. However, a major challenge is to accelerate the sluggish oxygen evolution reaction (OER) kinetics with a multistep proton‐coupled electron‐transfer process. Transition metal Ni‐ and Co‐based composites have been developed to replace expensive and scare noble metal based OER catalysts. So far, layered NiFe double hydroxide represents the best OER activity among all Ni‐ and Co‐based oxides. Herein, monodispersed ternary (Ni1‐xFex)12P5 nanocrystalline materials with tunable Ni/Fe ratios are reported as highly efficient OER electrocatalysts, exhibiting activity and stability surpassing noble metal OER catalysts including RuO2, IrO2, and superior to nickel phosphides, layered nickel‐iron double hydroxides, and other NiFe‐based OER catalysts. X‐ray photoelectron spectroscopy (XPS) studies reveals that enhanced charge transfer from the foreign metal (Fe) to the host (Ni) to P atoms and a strong synergistic effect exist in the composite (Ni1‐xFex)12P5 electrocatalysts, thus rendering the as‐prepared (Ni1‐xFex)12P5 nanocrystalline compounds (NCs) with a Ni/Fe ratio of 0.51/0.49, the highest OER activity with a small onset potential of 125 mV, a low Tafel slope of 39 mV dec−1, and a low overpotential of 216 mV, to achieve 20 mA cm−2 in an alkaline medium electrolyte (1.0 M KOH).

Self‐Powered Water‐Splitting Devices by Core–Shell NiFe@N‐Graphite‐Based Zn–Air Batteries

“…As shown in Figure S5 in the Supporting Information, the electrocatalysts exhibit the TOF of 0.45 (Fe 0.8 Ni 0.2 @N‐GR), 0.59 (Fe 0.2 Ni 0.8 @N‐GR), and 2.68 (Fe 0.5 Ni 0.5 @N‐GR) O 2 /s at the potential of 1.5 V, respectively, revealing that Fe 0.5 Ni 0.5 @N‐GR exhibits more active sites. These experimental results suggest that the intrinsic activity of NiFe@N‐GR is highly dependent on the Fe concentration in the metal core, where the electronic structures of surface active sites are efficiently turned . Besides, the Fe 0.5 Ni 0.5 @N‐GR also exhibits good stability for OER.…”

Operando Identification of Hydrangea-like and Amorphous Cobalt Oxyhydroxide Supported by Thin-Layer Copper for Oxygen Evolution Reaction

“…The TOF of the catalysts is shown in Figure S7a. CoOOH/Cu/Ni foam shows around 0.33 s –1 @η 300 , which is comparable to other works shown in Figure S7b. − …”

Synthesis of Flower‐Like Carbon‐Doped Nickel Phosphides Electrocatalysts for Oxygen Evolution Reaction

“…The high resolution XPS spectra of Ni, P and C elements from NiP/C‐850 are given in Figure (b‐d). As shown in Figure b, the peaks at 853.1, 856.5, and 861.9 eV are assigned to Ni 2p 3/2 binding energies, which can be ascribed to Ni in nickel phosphides, oxidized Ni species, and satellite peak, respectively . The peak at 853.1 eV is higher than the zero valence Ni (852.8 eV), suggesting the Ni species in Ni 12 P 5 have a small positive charge (Ni δ+ ).…”