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

Abstract

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.