Developing efficient and cost-effective electroctalysts to accelerate the sluggish kinetics of the oxygen evolution reaction (OER) is of great importance to emerging renewable energy technologies. In this work, a chemical sodium extraction of Na from low-cost Na0.71CoO2 electrocatalyst was demonstrated as an effective way to enhance its catalytic activity and durability toward enhancing OER. By continuously extracting sodium ions out of Na0.71CoO2 for 2 days, a low overpotential eta (0.44 V) at 10 mA cm(-2), a good mass activity (65.93 mA mg(-1)) and a small Tafel slope (55 mV dec(-1)) were achieved, which are superior to those of using precious metal oxide IrO2. XPS measurements and BET surface areas investigations suggest that the dramatic improved OER performance should be ascribed to several major factors, including formed Co4+ ions oxidized from Co3+, increased surface oxygen vacancies and enlarged specific surface areas occurred during the Na extraction process. The research here highlights the importance of tuning cation deficiency in Na-based oxides for further designing advanced OER electrocatalysts. (c) 2018 Elsevier Ltd. All rights reserved.