The Role of Metal-Organic Framework Induced Confinement Effects on Molecular Electrocatalysts Relevant to the Energy Transition.

Metal organic frameworks (MOFs) are promising materials for (electro)catalysis as they can improve stability, reusability, and catalytic current densities of molecular catalysts, thereby combining the advantages of homogeneous- and heterogeneous catalysts. However, much is unknown about the effects of confinement of a catalyst within an MOF on the overall catalytic behavior. The performance of a series of electrocatalysts confined in MOFs is compared to that of the corresponding homogeneous catalysts to evaluate to what extend the catalytic site is affected by confinement in terms of stability, activity, and selectivity. Together the examples discuss depict what happens to a catalyst when it is incorporated into an MOF, and recommendations are made on how to evaluate the electrochemical activity of an MOF in a way that allows for description of such confinement effects on the catalyst performance. It is noted that the limiting factor for the catalytic reaction in MOFs is found in 1) slow electron transport, 2) slow mass transport of reactants and products, or 3) a low activity of the catalytic site itself. Understanding the changes in mass- and electron transport and the resulting effects on catalytic mechanism is essential to be able to bring MOF systems to practical applications.