Two-Dimensional Cobalt Phosphate Hydroxide Nanosheets : A New Type of High-Performance Electrocatalysts with Intrinsic CoO₆ Lattice Distortion for Water Oxidation

Despite the recent advances in electrochemical water splitting, developing cost-effective and highly efficient electrocatalysts for oxygen evolution reaction (OER) still remains a substantial challenge. Herein, two-dimensional cobalt phosphate hydroxides (Co₅(PO₄)₂(OH)₄) nanosheets, a unique stacking-disordered phosphate-based inorganic material, are successfully prepared via a facile and scalable method for the first time to serve as a superior and robust electrocatalyst for water oxidation. On the basis of the detailed characterization (e.g., X-ray absorption near-edge structure and X-ray photoelectron spectroscopy), the obtained nanosheets consist of special zigzag CoO₆ octahedral chains along with intrinsic lattice distortion and excellent hydrophilicity, in which these factors contribute to the highly efficient performance of prepared electrocatalysts for OER. Specifically, Co₅(PO₄)₂(OH)₄ deposited on glassy carbon electrode (loading amount ≈0.553 mg cm^-2) can exhibit an unprecedented overpotential of 254 mV to drive a current density of 10 mA cm^-2 with a small Tafel slope of 57 mV dec^-1 in alkaline electrolytes, which outperforms the ones of CO₃(PO₄)₂ (370 mV) and Co(OH)₂ (360 mV) as well as other advanced catalysts. Evidently, this work has opened a new pathway to the rational design of promising metal phosphate hydroxides toward the efficient electrochemical energy conversion.