Metal–Organic Frameworks

Abstract

Metal-organic frameworks (MOFs) owing to their porosity, high surface area, and intrinsic metal sites, MOFs are frequently tested for their catalytic behavior in chemical catalysis, photocatalysis and electrocatalysis. As far as electrocatalysis is concerned, MOFs were used as electrodes for the oxidation/reduction of specific substrates (water, CO2, etc.); however, the poor conducting nature of these materials hampers such activity. To improve their conductivity, MOFs are frequently functionalized/composited with conducting materials such as carbon nanotubes, graphene, conducting polymers, and others or carbonized to render graphitized metal-oxide materials. Typically such composites show improved conductivity with active metal sites and hence they are ideal electrocatalysts compared to the pristine MOF materials. Water splitting, oxygen reduction reactions, and CO2 reduction reactions are frequently studied electrocatalytic reactions that are well established. In all these electrocatalytic reactions, noble metal catalysts such as Pt or IrO2/RuO2 serve as the benchmark catalysts. Their scarcity and high cost demand the search for cheaper alternatives with excellent electrocatalytic performance. As alternatives, inorganic transition metals, metal oxides, metal-free carbon composites, and others were widely investigated for their electrocatalytic behavior. Among these, MOF-derived catalysts secure a special place as they contain both the metal sites as well as conductive carbon matrices with high surface area, intrinsic porosity, and the like well suited for electrocatalysis.