Photoelectrocatalysis with Porous Coordination Polymers - Architectural Design, Morphology Control and Transport Properties

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The overall goal of this project is to establish an integrated metal-organic framework (MOF) platform for photoelectrocatalytic water splitting to overcome the need for sacrificial donor/acceptor schemes prevailing in particulate systems. Our approach thus addresses the uncharted interface between MOF photocatalysis and electrocatalysis by elucidating and controlling the very fundamentals of light-driven charge transport and redox catalysis in bio-inspired MOF-co-catalyst hybrid architectures based on porphyrin linkers. A prerequisite for the design of efficient photoelectrochemical cells will be the development of (i) highly porous MOF systems with light harvesting and electronically communicating subunits, and of (ii) synthesis strategies for high quality homogeneous, oriented MOF thin film electrodes. Our approach will be guided by insights into structure, dynamics, optical characteristics and electronic as well as ionic transport properties of the MOF films by solid-state NMR spectroscopy and impedance spectroscopy, as well as (photo)electrochemical analysis of the light-induced redox processes, feeding back into the design loop to create MOF photoelectrodes with high activity for hydrogen and oxygen evolution, reduced overpotentials and long-term stability. To accomplish this highly interdisciplinary task the research groups of B. V. Lotsch, M. T. Elm and J. Senker add their complementary skills in the synthesis and characterization of structural and transport properties. The Lotsch group has long standing expertise on the synthesis of MOF nanomaterials, the growth of MOF thin films and their post-synthetic modification of MOFs. The Lotsch group will develop photoactive porphyrin- and pyrene-based MOF systems, which will be interfaced with molecular and heterogeneous co-catalysts to orchestrate the light-induced multi-electron redox processes, and cast into high quality thin film architectures. For the structure elucidation of the MOF architectures the Senker group will provide a large repertoire of state-of-the art NMR crystallographic strategies. A thin film NMR probe will be developed in his group to analyze the structural integrity and porosity of the MOF films, to characterize the impact of confinement on the catalytic conversion, and to study the mechanism of light-induced charge carrier generation, to follow their mobility, and to probe the localization of excitons/polarons. Complementary experiments are carried out by M. T. Elm who is an expert on characterizing the electronic and ionic transport properties based on (photo)electrochemical techniques including impedance spectroscopy in various environments. In this way the nature of charge carriers, their concentrations and long-range transport, as well as the influence of defects on the transport and efficiency of the catalytic conversion will be probed.