In-situ electrochemical reconstruction of CoCO₃@FeOOH for boosting high-current-density oxygen evolution reaction and freestanding Zn-air battery

The activity of electrocatalysts in the oxygen evolution reaction (OER) is crucial for the widespread applications of water electrolysis and zinc-air batteries. Iron-cobalt-based catalysts attract considerably interests due to their high intrinsic activity and stability. However, it is still challenging in further promoting the OER efficiency at the high current density (500 mA cm(-2)) and understanding the real active sites during the OER process. In this work, the composite catalyst, cobalt carbonate (CoCO3) and iron oxyhydroxide (FeOOH), were successfully synthesized on the carbon cloth (CoCO3@FeOOH/CC) by a facile hydrothermal method. Through in-situ electrochemical activation, the CoFe2O4/CoFeOOH catalyst (R-CoCO3@FeOOH/CC) exhibits significantly improved OER overpotential, 190 and 238 mV at the current density of 50 and 500 mA cm(-2). By the in-situ Raman spectroscopy analysis and microscopy observations, the reconstructed structure CoFe2O4/CoFeOOH was identified. Based on the highly active OER performance of R-CoCO3@FeOOH/CC, it enables the continuous operation of freestanding ZABs at the ultralow charge voltage of 1.74 V in 5 mA cm(-2). These findings offer valuable insights for the design and application of high-performance iron-cobalt-based OER catalysts.