2D MOFs with Ni(II), Cu(II), and Co(II) as Efficient Oxygen Evolution Electrocatalysts: Rationalization of Catalytic Performance vs Structure of the MOFs and Potential of the Redox Couples

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 L₁ and angular L₂, 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 L₁ and L₂ 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.

Coordination polymers as heterogeneous catalysts in hydrogen evolution and oxygen evolution reactions

This article highlights various strategies of designing coordination polymers for catalysing water splitting reactions.

Design and Synthesis of Porous Nickel(II) and Cobalt(II) Cages

Coordination assemblies containing transition-metal cations with coordinatively unsaturated sites remain a challenging target in the synthesis of porous molecules. Herein, we report the design, synthesis, and characterization of three porous hybrid inorganic/organic porous molecular assemblies based on cobalt(II) and nickel(II). Precise tuning of ligand functionalization allows for the isolation of molecular species in addition to two- and three-dimensional metal-organic frameworks. The cobaltous and nickelous cage compounds display excellent thermal stabilities in excess of 473 K and Brunauer-Emmett-Teller surface areas on the order of 200 m2/g. The precise ligand functionalization utilized here to control phases between discrete molecules and higher-dimensional solids can potentially further be tuned to optimize the porosity and solubility in future molecular systems.

Mesoporous Metal-Organic Frameworks: Synthetic Strategies and Emerging Applications

Metal-organic frameworks (MOFs) have attracted much attention over the past two decades due to their highly promising applications not only in the fields of gas storage, separation, catalysis, drug delivery, and sensors, but also in relatively new fields such as electric, magnetic, and optical materials resulting from their extremely high surface areas, open channels and large pore cavities compared with traditional porous materials like carbon and inorganic zeolites. Particularly, MOFs involving pores within the mesoscopic scale possess unique textural properties, leading to a series of research in the design and applications of mesoporous MOFs. Unlike previous Reviews, apart from focusing on recent advances in the synthetic routes, unique characteristics and applications of mesoporous MOFs, this Review also mentions the derivatives, composites, and hierarchical MOF-based systems that contain mesoporosity, and technical boundaries and challenges brought by the drawbacks of mesoporosity. Moreover, this Review subsequently reveals promising perspectives of how recently discovered approaches to different morphologies of MOFs (not necessarily entirely mesoporous) and their corresponding performances can be extended to minimize the shortcomings of mesoporosity, thus providing a wider and brighter scope of future research into mesoporous MOFs, but not just limited to the finite progress in the target substances alone.

Robust high-connected rare-earth MOFs as efficient heterogeneous catalysts for CO2conversion

Two series of chemically and thermally stable rare-earth MOFs with a 12-connected hcp topology exhibit high catalytic activity towards the cycloaddition of CO₂and epoxides under mild conditions.