Hydrogen energy is recognized as a clean and sustainable alternative to fossil fuels, but its large-scale production remains limited by the cost and stability of electrocatalysts. In this study, Ni–Fe layered double hydroxide–modified nickel foam (Ni–Fe LDH@NF) was synthesized by the hydrothermal method and evaluated as a bifunctional electrode for water splitting. Electrochemical impedance spectroscopy (EIS) was employed to investigate charge-transfer behavior and interfacial resistance during operation. Nyquist plots showed that the electronic coupling between Ni and Fe significantly enhanced electron transport. At the same time, prolonged reaction time increased the charge-transfer resistance (Rct) because of surface oxidation and by-product accumulation. A linear relationship between Rct and reaction time was established, enabling the use of EIS data for the lifetime prediction of the electrode. Scanning electron microscopy revealed the structural degradation of the LDH layer after extended electrolysis, which is consistent with the impedance results. These findings demonstrate that Ni–Fe LDH@NF exhibits high catalytic efficiency and moderate durability for alkaline water splitting. The proposed EIS-based “sensing–diagnosis prediction” approach provides a quantitative method for evaluating electrode stability. This work suggests that Ni–Fe LDH is a promising non-noble metal catalyst and diagnostic sensor for future hydrogen energy applications.