From Peak to Peak: Exploring Electron Hopping and Mass Transport in Metal-Organic Frameworks

Sammanfattning: Incorporating molecular electrocatalysts into solid support structures combines the best of two worlds: their molecular nature allows precise structural tunability for selective and efficient conversion of small molecule substrates, while their structural integrity is greatly improved by the heterogeneous support matrix to allow for long-term stability and potentially industrial-scale applications. Metal-organic frameworks (MOFs) represent a potential class of materials to act as viable support scaffolds for hosting molecular catalysts for sustainable energy conversion, exhibiting well-ordered porous structures that can support high loading densities of catalyst species. The utilization of such heterogeneous electrocatalyst materials then relies on the transport of both mass and charge throughout the MOF to sustain electrocatalytic reactions. The concomitant transport of charge to activate the embedded catalyst species and mass transport of substrate and product molecules, as well as charge-balancing ions, to these activated catalysts must all maintain a balance within the framework to optimize the catalytic efficiency of the MOF-based material. The aim of this thesis is to explore mass and charge transport behaviors in electroactive and electrocatalytic MOF materials to gain insight into the mechanisms for these interwoven transport-related processes.The first part of this thesis introduces two novel electrocatalytic MOF materials and discusses the charge transport behaviors exhibited in each. Potential limitations in mass and charge transport processes which could influence the catalytic efficiency of the material are identified in each system. The second part of this thesis is centered on discussions of two electroactive MOF materials without embedded catalysts to gain a mechanistic understanding of mass and charge transport processes. The first of these studies focuses on the influences of imposed mass transport properties on the observed charge transport in a MOF, revealing the potential for multiple mechanisms of charge transport to be exhibited in one framework. The second study presents the mediated charge transport through an electroactive framework to a dissolved acceptor species to drive a chemical process, and kinetic analysis of the model pseudo-catalytic reaction is discussed.The work in this thesis highlights the importance of understanding the influences of mass and charge transport in electroactive and electrocatalytic MOFs for understanding the underlying mechanisms of these processes. Such knowledge would allow for the optimization of transport phenomena and result in more efficient MOF-based electrocatalysts.