Stabilizing High-Valence Ni/Fe Through Li Vacancy Engineering in Li<sub>(1–<i>x</i>)</sub>NiFeO<sub>2</sub>/NiFeOOH Heterostructures for Enhanced Oxygen Evolution Reaction
Wei Liu, Ruiqi Zhang, Chengyu Li, Xingwu Liu, Shuheng Tian, Xiao Ren, Ding Ma
Abstract
Ni/Fe (oxy)hydroxides have been extensively studied as highly effective electrocatalysts for oxygen evolution reactions (OERs) in alkaline media. The ability of stable, higher-valence Ni/Fe ions (Ni 3+ /Fe 3+ ) to enhance the OER activity has been well documented. In this work, we propose a cost-effective strategy for fabricating efficient OER catalysts through the electrochemical in situ delithiation of layered LiNi 1– x Fe x O 2 (LNFO) in an alkaline solution. This process leads to the formation of a NiFeOOH phase with highly oxidative Ni 3+ /Fe 3+ species at the catalyst surface. The ingenious heterostructure, resulting from the lithium vacancies generated on the LNFO surface, stabilizes the high-valence Ni and Fe species, significantly enhancing the intrinsic OER activity. The as-prepared NiFeOOH/LNFO catalyst shows good OER performance, achieving a current density of 10 mA cm –2 at an overpotential (η) of 250 mV. In situ Raman and quasi-in situ XPS analyses reveal that the continuous electrochemical delithiation process resulted in the presence of highly oxidative Ni 3+δ /Fe 3+δ species and more amorphous defective structures on the surface of NiFeOOH/LNFO during OER. The high activity ( U = 1.72 V at 1 A cm –2 ) and durability (continuous 45 h at 500 mA cm –2 ) of a membrane electrode assembly (MEA) cell also highlight its potential for practical large-scale applications.