Evolution of Ultrathin CoFe-Nanomesh for Oxygen Evolution Reaction: From Slit Pores to Ink-Bottle Pores

Abstract

The time-dependent mechanism underlying the formation of Co_0.8Fe_0.2(OH)_x-t nanomesh (nanomesh having 80 % Co and 20 % Fe, “t” represents materials synthesis time) has been identified towards the development of a highly effective catalyst for the oxygen evolution reaction (OER). Utilizing 2-ethyl imidazole (2-HEIM) as an etching reagent and the Ostwald ripening process enabled the evolution of nanomesh formation with a precise pore size of ink-bottle shape. Characterization techniques, including N₂-adsorption/desorption, and transmission electron microscopy (TEM) analyses, confirmed the evolution of pore structure from layered double hydroxide-like structure to hierarchical slit-pores to uniform ink-bottle pores after 24 h of synthesis with limited pore shrinkage attributable to iron redeposition at the pore entrances. Atomic force microscopy (AFM) showed a gradual reduction in nanomesh thickness with an increase in synthesis time up to 24 h, indicative of successful exfoliation. The best catalyst (Co_0.8Fe_0.2(OH)_x-24 h) was developed after 24 h of synthesis, having 3.8 nm ink-bottle-shaped pores on the basal plane of nanosheets with only 3–4 layers. Co_0.8Fe_0.2(OH)_x-24 h nanomesh exhibited the best catalytic performance, characterized by a 330 mV overpotential, a mass activity of 309.1 A/g, and a turnover frequency of 2.28 s⁻¹. Furthermore, electrochemical impedance spectroscopy indicated a low charge transfer resistance (5.9 Ω) and pseudoresistance (35.3 Ω), highlighting efficient electron transfer at the electrode/electrolyte interface and enhanced oxygen evolution reaction kinetics, respectively. An increased electrochemical surface area (70.74 cm²) and a high roughness factor of approximately 1010 underlined the importance of narrow mesopores in facilitating catalyst-electrolyte interactions and improving mass transport. The best material demonstrated remarkable stability during 25 h of electrolysis with a high average current density of 14.5 mA/cm². Hence, this research underscores the critical role of pore morphology in nanomeshes for optimizing catalytic performance and providing stability under vigorous gas evolution due to catalysis.