Co(II)-Imidazolate-Based Metal–Organic Frameworks as Efficient Bifunctional Electrocatalysts for Water Oxidation and Electroreduction of Nitrogen to Ammonia

Abstract

The electrochemical nitrogen reduction reaction (ENRR), when coupled with the oxygen evolution reaction (OER), presents a sustainable, safe, and energy-efficient alternative to the traditional Haber–Bosch process for ammonia synthesis. In this work, the rational design, synthesis, and electrochemical evaluation of two cobalt (II)-based metal–organic frameworks (MOFs) incorporating 2-methylimidazole (2-MeIm) and benzimidazole (BIm) as organic linkers is reported. Comprehensive voltammetric and in situ spectroelectrochemical studies confirm that Co(2-MeIm) and Co(BIm) MOFs exhibit excellent electrochemical stability and catalytic activity toward ENRR and OER. Notably, Co(BIm) MOF achieves an impressive ammonia production rate of 260 µg h⁻¹ mg⁻¹ with a Faradaic efficiency of 35.42%, significantly outperforming Co(2-MeIm) MOF (5.0 µg h⁻¹ mg⁻¹ and 15.0%, respectively). Furthermore, Co(BIm) MOF demonstrates outstanding OER performance, with a low Tafel slope of 50.1 mV dec⁻¹ and an overpotential of just 290 mV to reach a current density of 10 mA cm⁻². To the best of the authors knowledge, these ENRR and OER metrics represent among the highest reported for MOF-based electrocatalysts, highlighting the potential of tailored ligand environments in enhancing dual-function electrocatalytic performance.