General Trends in Structural Instability: Manganese‐Doped Nickel Layered Double Hydroxides in the Oxygen Evolution Reaction

Abstract Electrocatalytic water splitting is a key technology in the green transition, and catalysts based on abundant materials are especially attractive for large‐scale implementation. Ni‐based layered double hydroxides (LDHs) have shown significant potential as highly active electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. Their catalytic activity can be tailored through the incorporation of other transition metals. There is, however, little knowledge of the structural stability of doped Ni LDHs under OER conditions, information which is crucial for their application. This work identifies the structural instability of Mn‐doped Ni LDHs by tracking changes during OER activity in a gas diffusion electrode (GDE) setup. Mn‐substituted Ni LDHs with varying Mn ratios are investigated. Increasing the Mn ratio results in a 3% rise in LDH interlayer distance. A linear relationship between the OER overpotential and the LDH spacing is found, accompanied by a significant increase in the Tafel slope. All samples exhibited rapid degradation in intrinsic activity upon potential cycling, alongside structural modifications to the catalyst, studied in situ. Post‐degradation, all the catalysts demonstrated similar electrochemical properties and interlayer distances. These findings provide insights into a general degradation mechanism and restructuring of Mn‐doped Ni LDHs in operation.