Fast microwave-induced synthesis of solid cobalt hydroxide nanorods and their thermal conversion into porous cobalt oxide nanorods for efficient oxygen evolution reaction
Oxygen evolution reaction (OER) in water splitting is one of the most critical and more demanding half reaction in electrochemical devices and for that, designing of highly efficient and nonprecious-metal based electrocatalyst is required. Herein, we present fast microwave synthesis of solid nanorods of Co(OH)2 and then conversion into interconnected porous nanorods of Co3O4 by high temperature calcination for exposing active sites which offers high surface area resulted into faster exchange of intermediates and more efficient electron transfer for enhanced OER activities in alkaline solution. As-synthesized solid Co(OH)2 and calcined porous Co3O4 nanorod catalysts were characterized by scanning and transmission electron microscopy (TEM and SEM), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS) and finally OER performance has been investigated for water oxidation. FE-SEM and HR-TEM images reveals the formation of solid nanorods for as synthesized Co(OH)2 which were breaks and converted into porous interconnected nanorods after calcination at high temperature. In 0.1 M KOH aqueous electrolyte, solid Co(OH)2 @ 120 °C nanorods does not have favorable OER activity while Co3O4 @ 600 °C electrocatalyst exhibited low onset potential (1.55 V vs RHE) and Tafel slope (49 mV dec−1) holding robust stability more than 18 hours with negligible fading. This is mainly because the interconnected porous nanorods Co3O 4@ 600 °C catalyst possesses rich active boundary sites and short paths for charge/mass transport (higher reactivity of active sites) than Co3O4 @ 400 °C and Co(OH)2 @ 120 °C. Such a high catalytic activity is attributed to the suﬃcient exposure of accessible active sites of porous Co3O4 electrocatalyst.