Silver-integrated cobalt hydroxide hybrid nanostructured materials for improved electrocatalytic oxygen evolution reaction

Cobalt hydroxide Co(OH)2 is considered to be a potential material for electrocatalyst, especially for oxygen evolution reaction (OER), owing to the earth's abundance, environmentally benign nature, and redox-active properties of cobalt. Herein, we report the fabrication of pristine Co(OH)2 and AgNP-integrated Co(OH)2 (Ag–Co(OH)2) by simple wet chemical methods and explore the electrocatalytic OER activity in the alkaline medium. High-resolution transmission electro-microscopic (HR-TEM) analysis revealed featureless nanostructures for Co(OH)2 with coexisting amorphous and crystalline phases, as well as the inclusion of crystalline AgNPs in Ag–Co(OH)2. X-ray photoelectron spectroscopic (XPS) analysis confirmed the inclusion of metallic AgNPs and the presence of Co at a mixed oxidation state. Electrocatalytic OER studies indicated that pristine Co(OH)2 required the overpotential of 299 mV to achieve a geometric current density of 10 mA cm−2. The integration of AgNPs in Co(OH)2 (Ag–Co(OH)2) showed a gradual improvement in the OER activity. The optimized sample, Ag–Co(OH)2-5, required the overpotential of 253 mV to produce 10 mA cm−2 current density. Tafel slope analysis revealed a lower value upon AgNP integration and electrochemical impedance showed lower charge transfer resistance. The lower Tafel value and charge transfer resistance of Ag–Co(OH)2-5 indicated good chemical coupling and faster reaction kinetics at the electrode surface. AgNPs incorporation with Co(OH)2 also showed enhanced turn-over frequency, electrochemical active surface area, and double-layer capacitance. The fabricated hybrid Ag–Co(OH)2-5 catalyst also exhibited good stability over 60 h. Thus, the electrocatalytic activity of low-cost Co(OH)2 was improved by fabricating coexisting amorphous and crystalline phases and integrating noble silver nanoparticles.