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Rational design of high efficient and low cost oxygen evolution reaction (OER) electrodes is critical for electrochemical water splitting. Herein, we report Reevesite Ni−Fe layered double hydroxide (NiFe‐(CO32−)‐LDH) nanosheet arrays as novel OER catalysts in alkaline electrolyte. These self‐supported nanosheet arrays with a composition of Ni6Fe2(CO3)(OH)16 ⋅ 4H2O on Ni foam (NF) were synthesized by a one‐pot hydrothermal method, in which NF served as both the conductive substrate and Ni source. The morphology and OER activity can be tuned by iron concentration. In 1 M KOH, the optimized NiFe‐(CO32−)‐LDH catalyst only required overpotentials of 228 and 264 mV to deliver current densities of 10 and 100 mA cm−2, respectively, with a small Tafel slope of 37 mV dec−1. Remarkably, this catalyst also showed outstanding durability by long‐term operation for 20 h with 96 % retention. Our work provides attractive cost‐effective 3D catalysts for efficient and robust water oxidation at alkaline media. [ABSTRACT FROM AUTHOR]