Publication: Effect of structural modifications on the oxygen reduction reaction properties of metal-organic framework-based catalysts
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Date
2022
Journal Title
Metal-Organic Framework-Based Nanomaterials for Energy Conversion and Storage
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
In the present era, technological advancements are significantly progressed due to the rapid depletion of traditional energy resources. These energy resources are anticipated to be drained out due to their limited availability and nonrenewable nature in the near future. Therefore, intense research has to be carried out to explore alternative energy resources. A judicious solution to this menace is the exploitation of alternative energy sources which have minimum hazards to the environment. A very impactful method could be the use of electrochemical energy conversion systems such as fuel cells, metal-air batteries, etc. For these electrochemical energy conversion systems, oxygen reduction reaction (ORR) is the essential half-cell reaction that takes place at the cathode. However, the major hindrance which results in slow kinetics of the ORR is the conversion of O-O bond to O-H bond which requires high activation energy. Such a high energy barrier associated with this conversion limits its efficiency and conversion rates. Additionally, the high cost and mediocre durability of precious-metal-based catalysts such as platinum which made a benchmark for ORR put a limit on their commercial application. Therefore, it becomes very much essential to design and implement efficient and cost-effective electrocatalysts which can facilitate this conversion by alleviating the energy barrier. In the recent past, a unique class of functional material, known as metal-organic frameworks (MOFs) and their derivatives has gained limelight among the researchers worldwide, on account of its prominent efficiency as electrocatalysts for various electrochemical processes. MOFs are composed of metal ions or clusters bridged by organic linker molecules. The periodic structural design offers them a crystalline nature with high surface area and porosity. Meanwhile, on account of the hybrid nature of the structural components (i.e., organic as well as inorganic), MOFs display tailorable pore size and chemical environment rendering them variable physical and chemical properties. The porous nature of these MOFs results in the rapid diffusion of substrates through them thereby enhancing the number of active sites for the catalytic process. As the metal ion/cluster sites are isolated in the MOFs, they are analogical to the molecular catalysts. The structural design offers stability and robustness to the MOFs. Moreover, a careful approach toward structural and functional modification paves new ways of their utility for a large number of applications. Despite all these advantages, MOFs suffer from serious drawbacks of poor electrical conductivity and stability which hinders their utility as electrocatalysts for ORR. However, these shortcomings can be overcome by integrating these MOFs with highly conductive, advanced materials such as graphene, metal nanoparticles, nanocarbons, carbon nanotubes which results in the formation of MOF-based composites with improved electrical conductivity and stability. Additionally, thermal treatment methods like carbonization and pyrolysis can also be employed to convert MOFs and their composites to inorganic derivatives which find their applicability as ORR electrocatalyst on account of their superior conductivity and improved stability. Here, in this chapter, the ORR process and the role of MOFs as electrocatalysts for the ORR are described. In addition, different processes employed for the structural modifications of MOF and their successful utilization as the electrocatalysts for the ORR process are also described. � 2022 Elsevier Inc. All rights reserved.
Description
Keywords
Electrocatalyst, Metal-organic framework, Oxygen reduction reaction, Structural modification