High-Performance Overall Water Splitting Electrocatalysts\nDerived from Cobalt-Based Metal–Organic Frameworks

Abstract

The\ndesign of active, robust, and nonprecious electrocatalysts\nwith both H₂ and O₂ evolution reaction (HER\nand OER) activities for overall water splitting is highly desirable\nbut remains a grand challenge. Herein, we report a facile two-step\nmethod to synthesize porous Co-P/NC nanopolyhedrons composed of CoP_<i>x</i> (a mixture of CoP and Co₂P) nanoparticles\nembedded in N-doped carbon matrices as electrocatalysts for overall\nwater splitting. The Co-P/NC catalysts were prepared by direct carbonization\nof Co-based zeolitic imidazolate framework (ZIF-67) followed by phosphidation.\nBenefiting from the large specific surface area, controllable pore\ntexture, and high nitrogen content of ZIF (a subclass of metal–organic\nframeworks), the optimal Co-P/NC showed high specific surface area\nof 183 m² g^–1 and large mesopores, and\nexhibited remarkable catalytic performance for both HER and OER in\n1.0 M KOH, affording a current density of 10 mA cm^–2 at low overpotentials of −154 mV for HER and 319 mV for OER,\nrespectively. Furthermore, a Co-P/NC-based alkaline electrolyzer approached\n165 mA cm^–2 at 2.0 V, superior to that of Pt/IrO₂ couple, along with strong stability. Various characterization\ntechniques including X-ray absorption spectroscopy (XAS) revealed\nthat the superior activity and strong stability of Co-P/NC originated\nfrom its 3D interconnected mesoporosity with high specific surface\narea, high conductivity, and synergistic effect of CoP_<i>x</i> encapsulated within N-doped carbon matrices.