Controllable atomic defect engineering in layered NixFe1−x(OH)2 nanosheets for electrochemical overall water splitting

Abstract

Exploring efficient electrocatalysts through controllable defect engineering in materials with low-cost and earth-abundant elements is highly desired for overall water splitting. Herein, a hybrid electrocatalyst was successfully prepared by growing layered α-phase NiFe hydroxide on mildly oxidized carbon nanotubes (Ni_xFe_1−x(OH)₂/CNT) through a hydrothermal process. Then, Ni_xFe_1−x(OH)₂/CNT hybrids with defect structures accompanied by a change from Fe(OH)₂ to α-FeOOH were prepared via in situ oxidation of Fe(OH)₂ with H₂O₂ solution. In situ Raman spectroscopy was employed to investigate the change of the electrocatalysts under different potentials and identify the active sites in the oxygen evolution reaction (OER) process. In addition, X-ray absorption fine structure (XAFS) spectroscopy was employed to probe the metal defects in the hybrid. The outstanding electrocatalytic efficiency of Ni_1/2Fe_1/2(OH)₂/CNT with defects was accessible with a remarkably small overpotential of 244 mV and Tafel slope of 41 mV per decade for the OER in a 1.0 M KOH aqueous solution. Its bifunctional electrocatalytic efficiency was also evaluated using a two-electrode system, achieving a current density of 10 mA cm⁻² at an applied voltage of 1.64 V by loading the electrocatalyst on nickel foam. Furthermore, the high solar-to-hydrogen conversion efficiency of ∼10.3% for the bifunctional electrocatalyst indicates that the introduction of defects into the catalyst can significantly improve its catalytic efficiency, making it a promising low-cost catalyst for overall water splitting.