Two-Dimensional Cobalt Phosphate Hydroxide Nanosheets: A New Type of High-Performance Electrocatalysts with Intrinsic CoO 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(PO)(OH)) 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 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(PO)(OH) deposited on glassy carbon electrode (loading amount ≈0.553 mg cm) can exhibit an unprecedented overpotential of 254 mV to drive a current density of 10 mA cm with a small Tafel slope of 57 mV dec in alkaline electrolytes, which outperforms the ones of CO(PO) (370 mV) and Co(OH) (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.