EAGER: Unravelling the Origin of Electrocatalytic Activity of Metal Free Conjugated Polymers: Designing Carbon-Based Electrocatalysts

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The project explores the potential of designing electrocatalysts for sustainable energy based on oxygen-related reactions, especially the oxygen reduction reaction (ORR) essential to hydrogen fuel cells. While platinum-based cathode catalysts remain the most effective catalysts for hydrogen fuel cell applications, considerable progress has been made in the design and development of lower-cost transition metal alternatives, as well as a variety of carbon-based catalysts (such as carbon nanotubes). This Early-concept Grant for Exploratory Research (EAGER) project extends the capabilities of carbon-based ORR catalysts through the design, synthesis, and performance evaluation of conjugated polymers (CPs). The performance of CPs is currently limited by challenges in synthesizing electroactive CPs, as well as by knowledge gaps related to structure-function properties required to advance the technology to levels rivaling platinum. Thus, the project focuses on connecting synthetic parameters with materials properties (i.e. order and structure), while modulating the charge and spin distributions of the resulting CPs. Two specific aims will be pursued – 1) Synthesize electroactive polymers from heterocyclic monomers, and 2) Establish structure-to-function relationships. The experimental structure-function relationships thus obtained will provide valuable data needed for future theoretical/computational efforts to guide knowledge-driven optimization of non-metal carbon-based polymeric oxygen reduction electrocatalysts, as well as other potential applications of this class of electrochemical materials.The project is based on the central hypothesis that the electrocatalytic activity of CPs is related to the charge storage in these materials. Prior studies by the investigator and others have related the charge transfer in CPs to their polaronic states. In this system, the dopants define the extension of intramolecular conjugation lengths by delocalizing pi electrons along the chain of macromolecules, thereby facilitating the emergence of localized electronic levels in the forbidden bandgap of the CPs. While CPs are widely known for their performance in solar cells, and have also shown promising properties both as electroatalysts and precursors to electrocatalysts, their utilization has been hampered due to two main issues: a) their low solubilities, limiting their synthesis, and b) knowledge gaps related to the correlation of performance with the state-of-charge. The EAGER project will utilize a dry polymerization technique developed in the investigator’s laboratory to synthesize various CPs having a range of structural and chemical properties. The CPs are being synthesized and doped in one step via oxidative chemical vapor deposition (oCVD). The dopant concentration will be adjusted by controlling vapor phase composition in the oCVD process. The synthesized materials will be evaluated for their electrocatalytic properties in the ORR, thereby creating a platform for linking structure-to-properties relationships beyond the current state of the art. The project has the potential to establish a relationship between chemical structure and electroactivity in CPs, thus providing a basis for enhancing the performance and durability of carbon-based electrocatalysts. The project also provides a path for expansion of the materials selection and synthesis methods into other carbon-based materials such as conjugated microporous polymers and networks.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.