Facile and Green Synthesis of Well‐Defined Nanocrystal Oxygen Evolution Catalysts by Rational Crystallization Regulation

The development of catalysts for an economical and efficient oxygen evolution reaction (OER) is critical for clean and sustainable energy storage and conversion. Nickel–iron‐based (NiFe) nanostructures are widely investigated as active OER catalysts and especially shape‐controlled nanocrystals exhibit optimized surface structure and electronic properties. However, the structural control from amorphous to well‐defined crystals is usually time‐consuming and requires multiple stages. Here, a universal two‐step precipitation‐hydrothermal approach is reported to prepare a series of NiFe‐based nanocrystals (e.g., hydroxides, sulfides, and molybdates) from amorphous precipitates. Their morphology and evolution of atomic and electronic structure during this process are studied using conclusive microscopy and spectroscopy techniques. The short‐term, additive‐free, and low‐cost method allows for the control of the crystallinity of the materials and facilitates the generation of nanosheets, nanorods, or nano‐octahedra with excellent water oxidation activity. The NiFe‐based crystalline catalysts exhibit slightly compromised initial activity but more robust long‐term stability than their amorphous counterparts during electrochemical operation. This facile, reliable, and universal synthesis method is promising in strategies for fabricating NiFe‐based nanostructures as efficient and economically valuable OER electrocatalysts. A straightforward method is developed for synthesizing diverse transition metal‐based nanocrystals as catalysts for alkaline water electrolysis. Hydrothermal treatment of NiFe‐based hydroxides, sulfides, and molybdates produces nanosheets, nano‐octahedra, and nanorods with enhanced crystallinity. This adaptable, addictive‐free method allows large‐scale synthesis of well‐defined nanocatalysts, paving the way for applications in water electrolyzers, fuel cells, and metal‐air batteries.