Self-Limited Reconstruction of NiFe-Based Electrocatalysts Enables Thousand-Hour Water Oxidation at Ampere-Level Current Densities

Abstract

NiFe-based materials are highly promising electrocatalysts for the oxygen evolution reaction (OER), but they deeply reconstruct into the low-activity γ-NiFeOOH phase in alkaline media. Herein, we propose a corrosion strategy to achieve self-limited reconstruction (SLR) of NiFe-based electrocatalysts. Ultimately, the constructed (Fe0.67Ni0.33)OOH@FeP4 selectively reconstructs into highly active β-NiFeOOH rather than the less active γ-NiFeOOH. The SLR can be described as follows: when the (Fe0.67Ni0.33)OOH@FeP4 electrocatalyst is reconstructed into the β-NiFeOOH phase, the intrinsic characteristics of the electrocatalyst itself prevent the further transformation of β-NiFeOOH into the γ-NiFeOOH phase. In situ Raman, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations suggest that the synthesized (Fe0.67Ni0.33)OOH@FeP4 reconstructs into β-NiFeOOH featuring Fe−O−Ni linkages during OER, where electron transfer from Fe to Ni through Fe−O−Ni linkages suppresses the β-NiFeOOH to γ-NiFeOOH phase transition, thereby stabilizing the β-phase. DFT calculations reveal that the (Fe0.67Ni0.33)OOH@FeP4 enhances OER kinetics by promoting the formation of the *OOH intermediate. This mechanism enables the electrocatalyst to maintain excellent durability for over 1000 h in both the OER and overall water splitting at ≥1.0 A cm−2. In an anion-exchange membrane electrolyzer, it maintains 1.5 A cm−2 at 2.25 V for 150 h, superior to many NiFe-based electrocatalysts in the literature.