Controlled Reconstruction of F-Doped NiFe-LDH into a Hierarchical electrocatalyst for Saline Water Oxidation: Elucidating the Dual Role of Fluorine in Surface Stability and Active Phase Formation

Abstract

The rational design of hierarchical electrocatalysts is crucial for advancing saline water oxidation, a key technology for sustainable hydrogen production. This work demonstrates a novel strategy where a fluorine doped NiFe layered double hydroxide on nickel foam (F-LDH/NF) is transformed into a multi-level hierarchical catalyst (R-F-LDH/NF) via a targeted in-situ electrochemical process. This reconstruction creates core-shell nanosheets with a robust LDH core and a mesoporous, amorphous NiFeOOH surface, maximizing active site exposure and mass transport. The resulting catalyst exhibits exceptional OER performance in saline alkaline media, requiring only 262 mV to achieve 200 mA cm-2 with outstanding durability. Density functional theory (DFT) calculations reveal that fluorine incorporated in the precatalyst could serve three crucial functions. It enhances chloride repulsion at the surface for stability in saline electrolytes, triggers potential-driven desorption to initiate reconstruction into a defect-rich active phase, and optimizes the OER energetics of the resulting γ-NiFeOOH shell by stabilizing key reaction intermediates. This work provides a clear pathway for engineering advanced catalysts through controlled structural and chemical evolution.