CAREER: Blueprint for Unlocking New Energy Conversion Functionality in Chalcogenide Frameworks through Precisely Designed Composition, Electronic Structure and Surface Coordination

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Non-Technical Summary: An entirely new palette of materials is required to enable a sustainable terawatt-scale energy infrastructure. The development of functional materials with properties that facilitate renewable energy conversion and storage represents a promising approach that takes direct aim at this problem, one of the defining challenges of our time. This project, which is supported jointly by the Solid State and Materials Chemistry program in the Division of Materials Research and the Catalysis program in the Division of Chemical, Bioengineering, Environmental and Transport Systems, has far-reaching impact on both national and global sustainability, the accelerated discovery of economically viable energy conversion materials. The classes of materials being explored in this effort have properties such as electrical conductance, efficacy of solar-energy absorption, and electrochemical reactivity towards carbon dioxide reduction that are programmable as a function of their structure and elemental make-up. PI Velazquez’s study is comprised of an iterative combination of experimental research and computational modeling. The focus of this project is to combine state-of-the-art materials synthesis with experimental evaluation of electronic and structural properties in tailor-made solid-sate materials such that their properties of relevance to energy conversion can be accurately mapped to their composition and structure. This effort is augmented by a predictive computational modeling approach where favorable material properties are predicted for entirely new elemental compositions, thereby yielding new candidate materials in a closed-loop manner. In parallel with the experimental effort, undergraduate and graduate students are trained to solve problems at the interface between solid-state materials chemistry and chemical engineering; the training program specifically supports underrepresented minority and first-generation students. A major thrust of the educational plan involves curriculum supplementation through remote integration of modern solid-state chemistry and engineering research into high schools, thereby providing aspiring scientists with the tools required to successfully engage in STEM research. Technical Summary: This research systematically elucidates fundamental understanding of versatile classes of multi-dimensional metal chalcogenides, revealing material property descriptors through ex situ, in-situ, and operando measurements of atomistic and electronic structure in order to inform predictive models for electrochemical and photoelectrochemical reactivity. The PI hypothesizes that fine control over local metal-chalcogen coordination, intercalant charge density, and binary/ternary stoichiometry engenders desirable material properties that underpin energy conversion and storage functionality, including binding-site carbophilicity/oxophilicity, framework ionicity/covalency, and band gap/positions. To evaluate this hypothesis, the composition and local geometry of small-molecule adsorption sites in solid-state chalcogenide frameworks are systematically modified across the span of a substantial design space in order to experimentally and computationally elucidate trends in functionality that correlate with chemical and physical properties. Experimental results borne out of these modifications inform predictive machine learning-density functional theory models, which in turn generate candidate framework compositions that will engender optimal properties. This approach effectively closes a feedback loop between experiment and theory; as such, the anticipated products of this study are new metal chalcogenide materials and heterostructures from the 1D M2Mo6X6 (M = K, Rb, Cs; X = S, Se, Te), 2D MX2 (M = Ti, Mo, W; X = S, Se, Te), and 0D/3D MyMo6X8 (M = alkali, alkaline, transition, and/or post transition metal; y = 0–4; X = O, S, Se, Te) composition spaces that predictably yield oxygenated fuels, mediate bulk and interfacial charge-transport, and enable tunable photon absorption. More importantly, this research is expected to yield a materials design toolset that illustrates the importance of successfully iterative interplay between theory, synthesis, structure elucidation, and electronic structure studies when it comes to generating desirable solid-state properties. The intellectual merit of this work stems from its integrative approach to material design, where a foundational understanding regarding the effects of composition and structure on emergent physical properties, chemical reactivity, and energy conversion-related functionality is unraveled.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.