Reticular\nOne-Pot Synthesis of Synergic 4f(Ln)–3d(TM)\nHeterovalence and Heterobimetallic Europium–Copper MOFs: Emerging\nBifunctional Electrocatalysts for Efficient Water Splitting

A promising\npotential new electrocatalyst for water splitting could\nbe developed through the meticulous design and synthesis of diverse\nbimetallic metal–organic frameworks (MOFs). These MOFs would\nuse different or the same metals from the d and f blocks and could\nhave different oxidation states. This study focuses on developing\nan efficient bimetallic electrocatalyst, based on the rare-earth lanthanide\nseries element europium (Eu) and transition-metal copper (Cu) as the\nMOF using a one-pot hydrothermal method. As a result, a significant\n4f–3d heterovalent heterobimetallic MOF was obtained, and its\nelectrocatalytic activity toward water splitting was evaluated. Further,\nheterobimetallic MOFs with their mixed valence display an improved\nwater-splitting performance through synergistic effects. Linear-sweep\nvoltammetry (LSV) studies reveal that the bimetallic Eu–Cu-MOF\nrequired an overpotential of 133 mV for hydrogen evolution reaction\n(HER) and 240 mV for oxygen evolution reaction (OER) at a current\ndensity of 20 mA cm<sup>–2</sup> in 0.5 M H<sub>2</sub>SO<sub>4</sub> and 1 M KOH, respectively. Moreover, the long-term stability\nstudy exhibits a stable nature up to 20 and 16 h in 1 M KOH and 0.5\nM H<sub>2</sub>SO<sub>4</sub> solutions, respectively. The incorporation\nof Eu synergistically increases the adsorption and desorption ability\nof OH<sup>–</sup> and O<sub>2</sub> molecules toward OER, respectively.\nThe bimetallic MOF displayed excellent stability under acidic as well\nas alkaline conditions, indicating an exciting future for Eu–Cu-MOF\nin the field of electrochemical water splitting.