Two-Dimensional Co@N-Carbon Nanocomposites Facilely Derived from Metal-Organic Framework Nanosheets for Efficient Bifunctional Electrocatalysis.

Abstract

Metal-organic frameworks (MOFs) and MOF-derived nanomaterials have recently attracted great interest as highly efficient, non-noble-metal catalysts. In particular, two-dimensional MOF nanosheet materials possess the advantages of both 2D layered nanomaterials and MOFs and are considered to be promising nanomaterials. Herein, we report a facile and scalable in situ hydrothermal synthesis of Co-hypoxanthine (HPA) MOF nanosheets, which were then directly carbonized to prepare uniform Co@N-Carbon nanosheets for efficient bifunctional electrocatalytic hydrogen-evolution reactions (HERs) and oxygen-evolution reactions (OERs). The Co embedded in N-doped carbon shows excellent and stable catalytic performance for bifunctional electrocatalytic OERs and HERs. For OERs, the overpotential of Co@N-Carbon at 10 mA cm-2 was 400 mV (vs. reversible hydrogen electrode, RHE). The current density of Co@N-Carbon reached 100 mA cm-2 at an overpotential of 560 mV, which showed much better performance than RuO2 ; the largest current density of RuO2 that could be reached was only 44 mA cm-2 . The Tafel slope of Co@N-Carbon was 61 mV dec-1 , which is comparable to that of commercial RuO2 (58 mV dec-1 ). The excellent electrocatalytic properties can be attributed to the nanosheet structure and well-dispersed carbon-encapsulated Co, CoN nanoparticles, and N-dopant sites, which provided high conductivity and a large number of accessible active sites. The results highlight the great potential of utilizing MOF nanosheet materials as promising templates for the preparation of 2D Co@N-Carbon materials for electrocatalysis and will pave the way to the development of more efficient 2D nanomaterials for various catalytic applications.