Electric‐Field Assisted Hydrolysis‐Oxidation of MOFs: Hierarchical Ternary (Oxy)hydroxide Micro‐Flowers for Efficient Electrocatalytic Oxygen Evolution

Abstract

Water oxidation is the key process of electrocatalytic water splitting owing to its inherently slow kinetics. The ingenious design of microstructures for oxygen evolution reaction (OER) catalysts is an important way to accelerate the kinetics of the water splitting reaction. In this work, a facile electric‐field assisted alkaline hydrolysis‐oxidation strategy is proposed to prepare 3D layered micro‐flowers in situ constructed from ultra‐thin CoNiFe (oxy)hydroxide (CoNiFe‐OH) hexagonal plates by using Co/Ni/Fe metal‐organic frameworks (MOFs) as sacrificial templates and metal sources. The growth of the ballflowers can be accurately controlled by matching the hydrolysis rate of MOFs templates and the coprecipitation rate of metal ions. More importantly, continuous oxidation voltage can drive transformation of some hydroxides into oxyhydroxide with abundant oxygen vacancies. Benefiting from the open structure with multiple electroactive sites and optimized chemical composition, the layered CoNiFe‐OH micro‐flowers show appealing OER electrocatalytic performance with a low overpotential of 207 mV@10 mA cm−2 and robust durability over 60 h. This work provides a strategy to prepare non‐noble hierarchical nanostructured electrocatalysts for electrochemical energy conversion.

CO2-Assisted synthesis of a crystalline/amorphous NiFe-MOF heterostructure for high-efficiency electrocatalytic water oxidation

“…15 On the other hand, construction of heterostructures offers a great opportunity to modulate the local electronic structures at the tightly coupled interfaces, and implement the charge transfer process to reallocate the electronic density of the active sites. 16 Hence, the synergy of two strategies is supposed to be combined to design crystalline/amorphous MOF heterostructures ( c / a -MOF) for better OER performance.…”

Freestanding Cactus-Like Dual-Phase Bimetallic Metal–Organic Framework as a High-Efficiency Electrocatalyst for Water Oxidation

“…To explore the prominent electrochemical water oxidation performance, a three-electrode electrochemical measurement system is employed to access the performance as catalysts. The sharp oxidation peaks located approximately at 1.35–1.45 V (vs RHE) as shown in the LSV curves (Figure a) are relative to the transformation of Ni 2+ into Ni 3+ to form a highly active substance, facilitating the OER process . As demonstrated in Figure a,b, the NiFe-MOF@NF-II shows extremely impressive electrochemical OER activity, only a far smaller overpotential required to deliver a favored current density (277 mV@100 mA, 300 mV@200 mA, and 314 mV@300 mA) than those of pristine Ni-MOF@NF, pristine Fe-MOF@NF, and other dual-phase NiFe-MOFs@NF.…”

“…The sharp oxidation peaks located approximately at 1.35−1.45 V (vs RHE) as shown in the LSV curves (Figure 4a) are relative to the transformation of Ni 2+ into Ni 3+ to form a highly active substance, facilitating the OER process. 43 As demonstrated in Figure 4a,b, the NiFe-MOF@NF-II shows extremely impressive electrochemical OER activity, only a far smaller overpotential required to deliver a favored current density (277 mV@100 mA, 300 mV@200 mA, and 314 mV@300 mA) than those of pristine Ni-MOF@NF, pristine Fe-MOF@NF, and other dual-phase NiFe-MOFs@NF. Additionally, the effects of the individual porous NF conductive substrate toward the OER are also considered.…”

Surface, Interface and Structure Optimization of Metal‐Organic Frameworks: Towards Efficient Resourceful Conversion of Industrial Waste Gases

“…Besides being used as conventional adsorption and catalytic materials, new extensions have been made in material preparation, such as the precursor template method to evolve a variety of hierarchical structures. [140][141] Lu et al improved the conventional MOF-derived synthesis of nanoparticles and assembled CuO nanoparticles with different hierarchical structures using a solvent-free method. [142] As shown in Figure 8Aa-b, Cu 2 O and CuO nanoparticles with microsphere structures were obtained on the surface of the octahedral CuÀ BTC by heat treatment at different times in the pristine state.…”