Metal-organic framework derived hollow CoS₂ nanotube arrays: An efficient bifunctional electrocatalyst for overall water splitting

Self-supported hollow nanoarrays with hierarchical pores and rich reaction sites are promising for advanced electrocatalysis. Herein, we report a rational design of novel CoS₂ nanotube arrays assembled on a flexible support which can be directly utilized as an efficient bifunctional electrocatalyst for overall water splitting. Uniform wire-like metal-organic framework (MOF) nanoarrays were first fabricated and a sulfidation process by thermal treatment was carried out to transform the MOF arrays into CoS₂ nanotube arrays. The unique hollow CoS₂ tubular arrays are shown to provide high surface area for an efficient electrochemical reaction, and the well-defined electrical/mechanical connection to the substrate enhances both mass and electron transfer. The CoS₂ nanotube arrays exhibited a high electrochemical activity in catalyzing both oxygen and hydrogen evolution reactions, in terms of low onset potential, high current density and excellent stability. Using the CoS₂ nanotube arrays as catalysts, a water-splitting current density of 10 mA cm^-2 in alkaline solution is achieved with a cell voltage of 1.67 V, and the stable current can be maintained for 20 h even when the electrode is in a bent state.