Earth-abundant transition-metal-based metal–organic frameworks (MOFs) are of immense interest for the development of efficient and durable heterogeneous water splitting electrocatalysts. This repot explores the design of two-dimensional (2D) MOFs with redox-active metal centers (Ni­(II), Co­(II), and Cu­(II)) containing two types of electron-rich linkers such as bis­(5-azabenzimidazole), linear L 1 and angular L 2 , and aromatic dicarboxylates. The electron-rich linkers are considered to stabilize the higher oxidation state of the redox-active metal centers in the course of the electrocatalytic oxygen evolution reaction (OER) process. The 2D MOFs of L 1 and L 2 with Co­(II) (1 and 3) and Ni­(II) (2 and 4) have been produced via the conventional hydrothermal synthesis, while the MOFs of Cu­(II) (Cu@1 and Cu@3) are obtained by the postsynthetic transmetallation reaction of MOFs 1 and 3. The electrocatalytic OER activities of the six MOFs have been studied to explore the influence of the redox potential of the transition-metal quasi-reversible couples and the coordination environment around the redox-active metal centers in the electrocatalytic activity. The lowest overpotential of 370 mV exhibited by MOF 2 with the highest current density and TOF value indicates the importance of the presence of coordinated water molecules and the lowest redox potential value of the most favorable quasi-reversible couple Ni+2/Ni+3. These catalysts exhibit a remarkable stability up to 1000 OER cycles. These studies pave the way for the design of MOF materials toward the development of a promising heterogeneous OER electrocatalyst.

The efficiency of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the process of electrochemical water oxidation will determine the competence for mass distributions of sustainable energy conversion...

Recent studies on proton conductivity using pristine MOFs and their composite materials have established an outstanding area of research owing to their potential applications for the developments of high performance...

The design of highly efficient, cost-effective non-noble metal-based electrocatalysts with superior stability for overall water splitting (OWS) reactions is of great importance as well as of immense challenge for the upcoming sustainable and green energy conversion technologies. Herein, a convenient and simple in situ solvothermal method has been adopted to fabricate a self-supported, binder-free 3D electrode (Mn-MOF/NF) by the direct growth of a newly synthesized carboxylate-based pristine Mn­(II)-metal–organic framework (Mn-MOF) upon the conducting substrate nickel foam (NF). The binder-free Mn-MOF/NF electrode exhibits excellent performances toward OWS with ultralow overpotentials of 280 mV@20 mA cm–2 for the oxygen evolution reaction (OER) and 125 mV@10 mA cm–2 for the hydrogen evolution reaction (HER) with remarkable durability. Mn-MOF/NF can also attain a current density of 10 mA cm–2 with a low cell voltage of 1.68 V in a 0.1 M KOH solution in a two-electrode system for OWS. The direct growth of nonconducting electroactive Mn-MOF materials upon conducting substrate NF provides an excellent mass transport of the electrolyte with a relatively low contact resistance due to the strong catalyst–substrate contact and enhances the efficient electron transport for OWS. The redox chemical etching of the self-sacrificial substrate NF during solvothermal synthesis introduces redox-active Ni2+ in Mn-MOF/NF. Thus, the excellent OWS electrocatalytic activity can mainly be attributed to the bimetallic synergistic collaboration of the two redox active metal centers (Mn2+ and Ni2+) along with the excellent support surface of NF, which provides a high specific surface area and maximum utilization of the electroactive metal ion sites by preventing the self-aggregation of the active sites. The Mn-MOF/NF electrode also exhibits superb stability and durability for a prolonged time throughout the multiple cycles of full water splitting reactions. Therefore, this work elucidates a convenient and smart approach for constructing MOF-based bifunctional electrocatalysts for OWS.

Four new MOFs were shown to have appreciable proton conductivities, selective adsorption of water vapor over nitrogen and a tendency to selectively adsorb cationic dyes such as methylene blue and crystal violet.