Facile Synthesis of Two‐Dimensional Iron/Cobalt Metal–Organic Framework for Efficient Oxygen Evolution Electrocatalysis

Ir Nanoparticles Anchored on Metal-Organic Frameworks for Efficient Overall Water Splitting under pH-Universal Conditions

The construction of high-activity and low-cost electrocatalysts is critical for efficient hydrogen production by water electrolysis. Herein, we developed an advanced electrocatalyst by anchoring well-dispersed Ir nanoparticles on nickel metal-organic framework (MOF) Ni-NDC (NDC: 2,6-naphthalenedicarboxylic) nanosheets. Benefiting from the strong synergy between Ir and MOF through interfacial Ni-O-Ir bonds, the synthesized Ir@Ni-NDC showed exceptional electrocatalytic performance for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting in a wide pH range, superior to commercial benchmarks and most reported electrocatalysts. Theoretical calculations revealed that the charge redistribution of Ni-O-Ir bridge induced the optimization of H₂ O, OH* and H* adsorption, thus leading to the accelerated electrochemical kinetics for HER and OER. This work provides a new clue to exploit bifunctional electrocatalysts for pH-universal overall water splitting.

Metal-Organic Frameworks as Electrocatalysts

Transition metal complexes are well-known homogeneous electrocatalysts. In this regard, metal-organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF-derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

Interfacial Fe-O-Ni-O-Fe Bonding Regulates the Active Ni Sites of Ni-MOFs via Iron Doping and Decorating with FeOOH for Super-Efficient Oxygen Evolution

The integration of Fe dopant and interfacial FeOOH into Ni-MOFs [Fe-doped-(Ni-MOFs)/FeOOH] to construct Fe-O-Ni-O-Fe bonding is demonstrated and the origin of remarkable electrocatalytic performance of Ni-MOFs is elucidated. X-ray absorption/photoelectron spectroscopy and theoretical calculation results indicate that Fe-O-Ni-O-Fe bonding can facilitate the distorted coordinated structure of the Ni site with a short nickel-oxygen bond and low coordination number, and can promote the redistribution of Ni/Fe charge density to efficiently regulate the adsorption behavior of key intermediates with a near-optimal d-band center. Here the Fe-doped-(Ni-MOFs)/FeOOH with interfacial Fe-O-Ni-O-Fe bonding shows superior catalytic performance for OER with a low overpotential of 210 mV at 15 mA cm^-2 and excellent stability with ≈3 % attenuation after a 120 h cycle test. This study provides a novel strategy to design high-performance Ni/Fe-based electrocatalysts for OER in alkaline media.

Microwave-assisted rapid synthesis and activation of ultrathin trimetal-organic framework nanosheets for efficient electrocatalytic oxygen evolution

Ultrathin metal-organic frameworks (MOFs) nanosheets have been considered as one of promising electrocatalysts for oxygen evolution reaction due to their unique structures. However, the preparation process is subject to the low-yield exfoliation and time-consuming synthetic methods. And it still requires to be explored to develop an efficient strategy for regulation of surface electronic states of MOFs to enhance their electrocatalytic activities. Herein, we report a facile microwave-assisted synthesis of NiCoFe-based trimetallic metal-organic framework (MOF) nanosheets, which can achieve simultaneously rapid synthesis and activation of MOF for OER. The as-prepared Ni₄Co₄Fe₂-MOF nanosheets exhibit excellent OER activity and electrochemical stability, which can deliver a current density of 10 mA cm^-2 at a low overpotential of 243 mV with a small Tafel slope of 48.1 mV dec^-1. This work provides a facile method for the rapid synthesis of MOF nanosheets and also demonstrates an effective approach for regulating the electronic structure of MOFs for electrocatalysis.