The effects of Al substitution and partial dissolution on ultrathin NiFeAl trinary layered double hydroxide nanosheets for oxygen evolution reaction in alkaline solution

Recently, Ni–based layered double hydroxide (LDH) materials have attracted growing interest owing to the remarkable performance for oxygen evolution reaction (OER). Here we demonstrate the preparation of ultrathin Ni₃FeAl_x trinary LDH nanosheets with higher activity and stability than NiFe–LDH nanosheets for OER. The enhancement was derived from Al substitution, which increased the concentration of Ni³⁺ active sites on the catalyst surface. Besides, low-coordinated Ni and Fe atoms and defects were formed by partial etching/dissolution of Al³⁺ in alkaline solution, which further increased the activity towards OER. To improve the conductivity, Ni₃FeAl_x–LDH (x=0, 0.91, 1.27 or 2.73) nanosheets were also in-situ grown on three-dimensional-networked nickel foam. The binder-free Ni₃FeAl_x–LDH/Ni foam electrodes exhibited further improved catalytic performance compared to the electrodes made of powdery Ni₃FeAl_x–LDHs and nafion binder. The best OER performance was presented by Ni₃FeAl_0.91–LDH/Ni foam, showing a Tafel slope of 57 mV/dec, a low overpotential (304 mV) at the current density of 20 mA/cm², and a current density of 235 mA/cm² at 1.60 V (vs. RHE). Furthermore, the Ni₃FeAl_0.91–LDHs/Ni foam electrode showed excellent long-term stability, maintaining a stable overpotential of 320 mV at 20 mA/cm² after testing for 18 h.