MOFs for Electrocatalysis: From Serendipity to Design Strategies

Abstract

relentlessly shifted toward sustainable energy provision by means of interconversion of chemical and electrical energy. This development has motivated the exploration of efficient alternatives to the conventionally used high cost and scarce electrocatalysts like Pt for the oxygen reduction reaction (ORR) or the hydrogen evolution reaction (HER), as well as RuO 2 and IrO 2 for the oxygen evolution reaction (OER), that are primarily involved in important electrochemical energy systems such as fuel cells, water electrolyzers, metal-air batteries, etc. [1][2][3] Specifically, the sluggish reaction kinetics associated with the oxygen electrochemical processes have necessitated a lookout for more efficient ORR and OER electrocatalysts, which can be economically implemented for largescale applications. Any electrochemical reaction involving coupled diffusionreaction-conduction processes typically encompasses the interactions between a solid electrode, an electrolyte, and the dissolved reactants or products. Ideally, such interactions demand the need for high electric and ionic conductivity apart from a high surface area interface to ensure the effective interaction between the different phases involved in these reactions. [4] A classic catalyst design strategy would target improving the quality (in terms of the intrinsic activity) and quantity (in terms of the density) of the active sites. Additionally, availability of large specific surface area with substantial porosity and high charge transfer capability are the prerequisites of the "ideal" electrocatalyst architecture. In this direction, a plethora of materials including carbon allotropes, [5] metal chalcogenides, [6] organometallic complexes, [7] conducting polymers [8] and their composites have been tested for their electrocatalytic activity. A recent class of porous materials, popularly known as metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have been extensively explored as electrocatalysts or as precursors to derive efficient heterostructures owing to their synthetic flexibility besides customizable electronic and chemical properties. [9][10][11][12] These highly crystalline materials are well known for their ultrahigh specific surface area of up to 10 000 m 2 g −1 , wide pore size distribution, modifiable framework composition, and controllable pore volumes. The possibility to employ different metal ions-ligand coordination combinations with varying degrees of connectivity has stimulated the realization of ≈20 000 MOF The rapid upsurge of metal-organic frameworks (MOFs) as well as MOFderived materials has stimulated profound interest to capitalize on their many potential untapped benefits in electrocatalysis for energy applications. The possibility of tuning the metal-ligand junctions of the MOF architecture opens new avenues to design robust, extended heterostructures for addressing the present-day energy challenges. Interestingly, despite having detailed crystallographic information, it is often difficult to envisage the interplay of ...

Recent Approaches to Design Electrocatalysts Based on Metal–Organic Frameworks and Their Derivatives

“…Although recent tremendous progress in the field of OER has been witnessed based on these pristine MOFs, their catalytic activities are still limited to meet the increasing demand . MOF‐derived electrocatalysts have shown promising advantageous characteristics such as highly conductive carbon network, porous nanostructures, large surface area, diverse heteroatoms doping (e.g., N, O, S, and P) and homogeneously distributed metal atoms or metal compounds, which are a benefit for OER . In this section, the concepts based on the composition engineering, the structure or morphology engineering, and the substrate engineering for designing MOF‐derived catalysts for improving the OER performance will be discussed.…”

“…In practical use, electrocatalysts are usually operated in harsh conditions, such as strong acidic and alkaline solutions . However, most of the pristine MOFs cannot sustain their structure in harsh conditions . Taking this drawback as advantages, researchers developed MOF‐derivatives by facile immersing pristine MOF into an alkaline environment .…”

Importance of Electrocatalyst Morphology for the Oxygen Reduction Reaction

“…For 3D NPs, MOFs are promising precursors in preparing 3D M−N−C electrocatalysts for ORR after pyrolysis at high temperature (>700 °C) . MOFs have diverse porous structure and varied elemental composition.…”

“…For 3D NPs, MOFs are promising precursors in preparing 3D MÀ NÀ C electrocatalysts for ORR after pyrolysis at high temperature (> 700°C). [154][155][156][157][158][159][160][161][162][163][164] MOFs have diverse porous structure and varied elemental composition. For instance, Wang et al prepared a Cu@FeÀ NÀ C electrocatalyst by calcinating the Fe-and Cu-doped ZIF-8 (Figure 8a-c).…”

Polymers of Intrinsic Microporosity in Triphasic Electrochemistry: Perspectives

“…A wide range of novel mesoporous and microporous materials have emerged such as zeolites, [16,17] metal organic frameworks, [18,19] and covalent organic frameworks [20] with the an open network of micropores (ranging typically from 0.5 nm to 5 nm or higher). Many polymers are known to be microporous and gas permeable and particularly glassy polymers with high excess free volume are of interest [21] for example in gas separation.…”