Metal-Organic Frameworks for Energy Applications

This dissertation presents the photochemical (Chapter 2), electrochemical (Chapters 3, 5), and photophysical (Chapter 4) properties of light harvesting and catalytic molecules incorporated into metal-organic frameworks (MOFs). Chapter 1 presents an overview of the goals, purposes, and background materials for the subsequent chapters. Chapter 2 reports cobalt-porphyrin moieties incorporated into two MOF architectures and their catalytic activities for photochemical hydrogen production in an aqueous media. By inserting zinc and cobalt ions into the porphyrin centers to serve as the photosensitizer and catalyst respectively, MOFs capable of hydrogen generation were developed within a single material without the need of a separate co-catalyst. The resulting assemblies give TONs as high as 75 after five hours irradiation in an acidic medium through a putative Co(III)-H intermediate, outperforming their homogenous counterparts by up to 15 times. Chapter 3 presents electrocatalytic proton reduction with Hf12-porphyrin MOFs covalently tethered to carbon nanotubes (CNTs). Covalent attachment of the MOF nanoplates to conductive CNTs improves electron transfer from the electrode to the Co-porphyrin active sites, leading to effective proton reduction. The Hf12-CoDBP/CNT assembly afforded a turnover number of 32,000 in 30 minutes with an average turnover frequency of 17.7 s-1, placing it among the most active Co-based molecular catalysts. Chapter 4 describes the photophysical and photochemical properties of a [Ru(bpy)2(py)2]2+ complex confined within a zinc-oxalate MOF (Ru@MOF). The MOF perfectly encapsulates [Ru(bpy)2(py)2]2+ complexes, thereby altering their vibrational and electronic states through sterics and by removing the effects of solvents. As a result, the photoluminescence lifetime and quantum yield of the material significantly increase, likely through the destabilization the dd-state. The photochemical stability of [Ru(bpy)2(py)2]2+ in Ru@MOF also significantly increases due to the shutdown of photosubstitution processes. This stability can be leveraged into further studies including transient absorption and photocrystallography among other spectroscopic techniques. Chapter 5 describes the incorporation of a precious metal free cobalt-terpyridine catalyst into two-dimensional metal organic layers (MOLs) for hydrogen production in acidic media. The Co-TPY MOL effectively stabilizes ultrasmall cobalt nanoparticles for hydrogen production with TOFs as high as 4300 hr-1 in pH=1 at a low overpotential of 715 mV