In Situ Reconstructed Crystalline–Amorphous CuNi Nanotubes Unifying Activity and Stability for Oxygen Evolution

Development of durable and active noble‐metal‐free catalysts for the alkaline oxygen evolution reaction (OER) remains a critical challenge. Conventional electrocatalysts typically suffer from an intrinsic trade‐off between activity and stability. Here, we report an in situ electrochemically reconstructed CuNi nanotube with a crystalline–amorphous heterostructure, featuring a conductive crystalline alloy core encapsulated by an amorphous nickel oxide shell. The metallic core provides a high‐conductivity framework for rapid charge transfer and maintains structural integrity, while the in situ derived amorphous phase maximizes the density of accessible active sites and passivates the metallic core against oxidative corrosion. The optimized catalyst achieves an overpotential of 229 mV at 10 mA cm −2 and operates stably for over 1000 h in alkaline OER, reconciling the catalytic activity and stability. Mechanistically, operando Raman spectroscopy and electron energy loss spectroscopy elucidate the dynamic valence modulation and surface phase evolution as the origin of its performance. Overall, this work establishes controlled electrochemical reconstruction as a transformative paradigm for unifying catalytic activity and stability, providing a design principle for advanced, earth‐abundant OER electrocatalysts.