ABSTRACT

Electrochemical catalysis can be used to generate hydrogen from water, thereby offering a sustainable alternative to conventional processes that generate hydrogen from natural gas or petroleum. In recent years, a class of low-cost chemical materials, known as transition metal dichalcogenides (TMDCs), have been identified as promising materials for water-based hydrogen production to power fuel cells and as a raw material for the manufacture of chemicals. Despite their promise, additional scientific understanding and engineering design will be needed to maximize the performance of the dichalcogenide materials to levels rivaling more expensive state-of-the-art platinum-based catalysts. To that end, the project will explore fundamental aspects of the dichalcogenide materials and their effectiveness for hydrogen generation utilizing a unique reactor system. The research will help pave the path to a sustainable energy and chemicals future while also laying ground work for long-term competitiveness of the U.S. in the fuels and chemical manufacturing sectors. The research will be integrated with educational and outreach activities emphasizing participation by under-represented groups.

The project seeks answers to the extent that electronic transport properties and interfacial effects (rather than the free energy of hydrogen adsorption) limit the overall rate of the hydrogen evolution reaction (HER) on TMDCs. A single-crystalline flake nanodevice will be employed as a HER micro-reactor, which allows precise control of the density and types of catalytic sites, and accurate measurements of charge transport within the catalyst, as well as the Schottky barrier at the catalyst/current collector interface. Three aims are proposed to study how the TMDC electrical properties, interfacial Schottky barrier, and the hydrogen adsorption free energy change as a function of 1) the phase transition from the semiconducting 2H to the semi-metallic 1T' phase of TMDCs, 2) strain engineering of TMDCs, and 3) different current collectors. The changes in the various properties will be correlated with the measured HER activities using a standard three-electrode cell coupled to the individual TMDC nanodevices in sulfuric acid electrolyte solution. Semiconducting MoS2 and WS2, and semi-metallic MoTe2 and WTe2 nanoflakes will be used for the proposed research, grown by chemical vapor deposition or exfoliated mechanically from bulk crystals grown by chemical vapor transport. Beyond optimization of TMDC materials for HER, the nanodevice platform can be applied to other electro- and photo-catalysts to correlate their catalytic properties to critical parameters such as energetics of catalytic sites, equilibrium electrical properties, interfacial effects, and excited states induced by photons. The project will link the research to education and outreach activities via three outreach programs targeting, respectively, the general public (a weekend Energy symposium at Yale West Campus), under-represented undergraduate students (a monthly seminar series given by minority faculty members), and local high school students (a demonstration HER kit and workbook based on TMDC thin films).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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