Multiscale design of 3D metal–organic frameworks (M−BTC, M: Cu, Co, Ni) via PLAL enabling bifunctional electrocatalysts for robust overall water splitting

Abstract

Multiscale structural engineering of high-performance bifunctional electrocatalysts to influence hydrogen and oxygen evolution reactions (HER and OER) has a significant role in overall water splitting. Thus, we successfully designed a new strategy and synthesized transition-metal-based 3D metal–organic framework (MOF) materials having various architectures, namely, Cu–BTC, Co–BTC, and Ni–BTC, by pulsed laser ablation in dimethylformamide. The coordination between the metal and carboxylate moieties of the ligand, crystalline structure, phase purity, morphology, thermal stability, and oxidation states were illustrated using physical characterization techniques. Further, intrinsic properties of the MOF materials were studied using electrocatalytic reactions toward HER and OER in an alkaline medium. Among the synthesized MOF materials, the Co–BTC electrocatalyst showed a very low overpotential of 437 mV toward HER at a constant current density of 10 mA cm−2 in 1.0 M potassium hydroxide. The derived Tafel slope and Rct values are 115.1 mV dec−1 and 2.77 Ω cm−2, respectively. Similarly, OER studies reveal that the Co–BTC MOF showed robust activity with low overpotential of 370 mV at 10 mA cm−2. Finally, the optimal Co–BTC MOF electrode required 2.03 V of cell potential to deliver 10 mA cm−2 in a dielectrode (Co–BTC ∥ Co–BTC) electrolysis system with long-run stability. The present report reveals a new possibility for the innovation in robust HER and OER bifunctional electrocatalysts using nonprecious metallic MOF materials.