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 Co0.8Fe0.2(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 OER. Utilizing 2-ethyl imidazole as an etching reagent and the Ostwald ripening process enabled the evolution of nanomesh formation with a precise pore size of inkbottle shape. Material characterization 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. 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 (Co0.8Fe0.2(OH)x-24h) 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. Co0.8Fe0.2(OH)x-24h 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. 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.