CAREER: Transition Metal Chalcogenide Clusters: Preformed Building Blocks for Framework Materials

NON-TECHNICAL SUMMARY

Bulk transition metal chalcogenides (TMCs), are important materials for energy storage, electronic devices, and catalysis. However, TMCs are typically synthesized at high temperatures and pressures or are isolated using exfoliation techniques. Traditional synthetic approaches to TMC materials lack precise structural control, thus limiting their ability to be rationally tuned for specific applications.

With this CAREER project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Prof. Christopher Bejger studies how nano-sized fragments of TMCs can be used as building blocks for multidimensional scaffolds with high surface areas, known as metal-organic frameworks (MOFs). MOFs offer robust stability, crystalline structures, and can be predictably synthesized.

The resulting hybrid materials share features of both conventional, bulk TMCs and crystalline MOFs. Frameworks made from TMC units undergo multiple, reversible oxidation state changes. Thus, TMC-MOFs are relevant to the study of nanoelectronics and future charge storage devices.

The design of these materials provides inspiration for an integrated education component. The PI plans and fabricates an interactive Nanoscale Science Pop Up Museum, influenced by the principles of molecular and materials design, in collaboration with Prof. Rachel Dickey at the UNC Charlotte School of Architecture.

The PI and his architecture colleague also partner with the Charlotte Teachers Institute (CTI) to present a seminar series for Charlotte-Mecklenburg School (CMS) teachers titled "Design Matter(s)" and host both science and art educators in a Summer Research Experience for Teachers. TECHNICAL SUMMARY

This research project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, investigates a new class of redox-active metal-organic frameworks (MOFs) comprising transition metal chalcogenide (TMC) molecular clusters. TMC clusters exhibit rich electrochemical behavior and have a propensity to undergo reversible, multi-electron transfer events.

However, their use in MOF chemistry is limited by a lack of suitable synthetic protocols. The Bejger research group uses phosphine ligands with ancillary functional groups to incorporate pre-formed, atomically defined, metal-sulfide units into multidimensional frameworks. Several strategies are explored to expand the stoichiometric and structural combinations of precursors of the general formula MxSy (M= Ni, Co, Mo, Fe).

The composition, topology, and surface areas of the materials are tailored to control the arrangement and charge of redox-active clusters. TMC clusters have mixed-valence, delocalized, metal-chalcogen cores that provide structural integrity across oxidation states and serve as electron reservoirs. Select TMC-MOFs that undergo stable charge/discharge cycling are studied for energy storage applications.

TMC-MOF cathodes that mediate bifunctional charging are investigated for use in lithium ion batteries. The educational component of this proposal aims to increase civic engagement with materials chemistry through the lens of architecture and design. A pop-up museum is designed and fabricated as a collaborative project with the UNC Charlotte School of Architecture.

The educational plan is multifaceted to emphasize links between MOF topology, reticular synthesis, and architecture. The ideas presented in the museum concept are disseminated and developed into a curriculum for local teachers through a partnership with the Charlotte Teachers Institute (CTI).

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.