Dithiolate-based metal-organic frameworks for electrocatalytic hydrogen evolution

Abstract

In the face of a looming climate crisis, immediate action needs to be taken to decarbonize the current fossil-fuel-dominated energy economy by adopting a more sustainable alternative. Thanks to the alliance between scientific breakthroughs and policy support, recent years have witnessed the rapid growth in renewable electricity generation using solar and wind energy. However, the integration of renewables into other major energy sectors, such as transportation and thermal production, is still very limited. To address this challenge, electrocatalysis provides a feasible solution, where abundant small molecules are converted into value-added products via the input of renewable electricity to realize the storage of renewables in chemical bonds. The products can then be consumed as fuels for transportation or thermal production, or as chemical feedstocks in industrial processes. The key to realizing this electrocatalysis-based sustainable energy future is to develop highly efficient electrocatalysts that are composed of abundant elements and can facilitate chemical catalysis under mild conditions. ? In this dissertation, several electrocatalysts that are based on metal-organic frameworks (MOFs) are developed for green hydrogen production from water. Electrocatalytic hydrogen production is of particular interest because hydrogen is a very important chemical feedstock in industrial productions and a promising carbon-free energy carrier. In recent years, MOFs have emerged as an extensive class of highly functional materials with unique properties such as high porosities, large surface areas, and extraordinary structural and compositional variabilities. The application of MOFs in clean energy is an emerging field of research and is of great significance in the context of the current climate crisis. A brief outline of this dissertation is provided below: ? Chapter 1 presents a general introduction of the dissertation, including a brief discussion on the current global energy status, the fundamentals of electrocatalytic hydrogen production, general design principles of electrocatalysts, as well as the frontiers in MOF-based electrocatalysis. In Chapter 2, the HER performance of a known dithiolene-based MOF, the cobalt triphenylene-2,3,6,7,10,11-hexathiolate (THT) MOF, is optimized by unraveling the reaction mechanism and identifying the key factors that dictate the overall catalytic performance. The optimization results in the most active MOF-based electrocatalyst for hydrogen production that comprises only earth-abundant elements. Chapter 3 discusses the role of metal centers in the HER activity using the examples of a series of iron and cobalt/iron mixed-metal dithiolate MOFs. In Chapter 4, a conductive three-dimensional dithiolene-based MOF, the Cu[Ni(2,3-pyrazinedithiolate)2] MOF, is investigated as an HER electrocatalyst for the first time. Lastly, Chapter 5 presents the synthesis and HER characterization of a diselenolate-based MOF, an analogous derivative of the dithiolate MOFs. This study is to highlight the role of the chalcogen within the ligand, which is inspired by nature where the selenium-containing [NiFe] hydrogenase displays much higher activity than its sulfur-only analog for hydrogen production.