Reticular One-Pot Synthesis of Synergic 4f(Ln)–3d(TM) Heterovalence and Heterobimetallic Europium–Copper MOFs: Emerging Bifunctional Electrocatalysts for Efficient Water Splitting

A promising potential new electrocatalyst for water splitting could be developed through the meticulous design and synthesis of diverse bimetallic metal–organic frameworks (MOFs). These MOFs would use different or the same metals from the d and f blocks and could have different oxidation states. This study focuses on developing an efficient bimetallic electrocatalyst, based on the rare-earth lanthanide series element europium (Eu) and transition-metal copper (Cu) as the MOF using a one-pot hydrothermal method. As a result, a significant 4f–3d heterovalent heterobimetallic MOF was obtained, and its electrocatalytic activity toward water splitting was evaluated. Further, heterobimetallic MOFs with their mixed valence display an improved water-splitting performance through synergistic effects. Linear-sweep voltammetry (LSV) studies reveal that the bimetallic Eu–Cu-MOF required an overpotential of 133 mV for hydrogen evolution reaction (HER) and 240 mV for oxygen evolution reaction (OER) at a current density of 20 mA cm–2 in 0.5 M H2SO4 and 1 M KOH, respectively. Moreover, the long-term stability study exhibits a stable nature up to 20 and 16 h in 1 M KOH and 0.5 M H2SO4 solutions, respectively. The incorporation of Eu synergistically increases the adsorption and desorption ability of OH– and O2 molecules toward OER, respectively. The bimetallic MOF displayed excellent stability under acidic as well as alkaline conditions, indicating an exciting future for Eu–Cu-MOF in the field of electrochemical water splitting.