With a growing demand for clean and renewable energy associated with water splitting, regenerative fuel cells, metal-air batteries, etc., exploring an efficient and cost-effective electrocatalyst with superior durability for oxygen evolution reaction (OER) is of great significance. In this study, a unique CoOx embedded nanoflower microstructure (Co-0.6-PyNa) has been synthesized via an extremely facile one-step, highly scalable aqueous method under mild conditions, by using Co(COOH) 2 as the precursor and pyrrole as the structure-directing agent. The Co-0.6-PyNa exhibits the excellent electrocatalytic activity toward OER in 1M KOH solution with an overpotential of as low as 299 mV and a small Tafel slope of 67 mV dec (1), which is comparable to the commercial RuO2, along with superior operational stability to RuO2. The high OER catalytic performance of Co-0.6-PyNa has been reasoned to originate from the exposure of abundant CoOx active species uniformly dispersed on the nanoflakes due to its high specific surface area and the intrinsic extraordinarily high activity of CoOx active species. This work provides a promising strategy to fabricate efficient, stable and low-cost OER electrocatalyst, which is expected to promote the development of OER-related energy storage and conversion technologies. (C) 2018 Elsevier Ltd. All rights reserved.