Two-Dimensional Cobalt Phosphate Hydroxide Nanosheets: A New Type of High-Performance Electrocatalysts with Intrinsic CoO 6 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 (Co ₅ (PO ₄ ) 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 CoO ₆ 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, Co ₅ (PO ₄ ) 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 CO ₃ (PO ₄ ) 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.