Structural Evolution and Oxygen Evolution Performance of NiFe‐Based Electrocatalysts in Phosphate‐Containing Electrolytes at Non‐Extreme pH

Solid/liquid interfacial interactions play an important role in electrochemical reactions when supporting electrolyte components, such as buffer anions, interact directly with catalyst surfaces. Here, we show that phosphate addition selectively suppresses the oxygen evolution reaction (OER) performance of Ni‐rich NiFeO x electrocatalysts at pH ∼9. Operando Raman spectroscopy and Ni K‐edge X‐ray absorption near‐edge structure/extended X‐ray absorption fine structure (XANES/EXAFS) analyses suggest that phosphate decreases a high‐potential γ‐NiOOH‐like state and attenuates the associated Ni‐centered structural response. No Fe K‐edge change larger than the experimental uncertainty was resolved during OER. The current and redox response recovered immediately after phosphate was removed, demonstrating a reversible short‐term electrolyte effect. In contrast, on‐off cycling through the Ni reduction region caused progressive loss of redox charge and catalyst material, particularly for Ni‐rich compositions. These findings highlight the importance of integrated electrolyte–electrocatalyst design for improving OER performance and durability, especially under mild pH conditions.