Phase-transfer synthesis of α-Co(OH)2 and its conversion to CoO for efficient electrocatalytic water oxidation

Water splitting is an attractive way to produce recyclable hydrogen energy resource. The oxygen evolution reaction (OER) is the rate-determine step of water electrolysis. The exploring of low-cost, highly efficient and durable electrocatalysts for OER is thus extremely important. In this work, we developed a facile two-phase protocol to fabricate an α-Co(OH)2 using sodium oleate as the phase-transfer surfactant. The crystallinity and structure of the α-Co(OH)2 was regulated by heat treatments toward enhanced electrocatalytic OER activity. With the calcination of the as-prepared α-Co(OH)2 at 200 °C, a networked and well-dispersed CoO nanoparticles were formed. The CoO sample afforded an OER current density of 10 mA cm−2 under a low overpotential of 312 mV in a 1 mol L−1 KOH aqueous solution. The high activity of the CoO material is believed to be associated with its ultra-small particle size and plentiful open spaces in the material, both of which can provide abundant surface catalytic sites.