Over the past decade researchers have come up with various CO2 reduction catalysts which mimic nature but the main challenge they faced was the insolubility of these catalysts in the aqueous medium. Carbon monoxide dehydrogenases (CODHs) from anaerobic organisms which is a reversible electrocatalyst with zero overpotential contains [Ni4Fe-4S] cluster that catalyzes the interconversion of CO2 and CO. Inspired by this example from nature, we are designing metalloproteins that include the engineering of protein sequences, metal cofactor and metal center. In order to account these factors, we adopted a heme protein which can reduce CO2 to CO and CH4 selectively over proton reduction by adjusting the pH and buffer conditions. The reduction studies were done using a heterogeneous electrochemical method where the protein was mixed with CNT (carbon nanotubes) and PBSE (1-Pyrene butyric acid N-hydroxysuccinimide ester) to make a composite. The composite was dried over a glassy carbon electrode (GCE) or rod to analyze the cyclic voltammogram (CV) and controlled potential experiment (CPE). The CV data demonstrates the conversion of low valent Fe (I) to Fe (0) which we believe is the active species responsible for the catalytic conversion of CO2 to CO. The formation of H+ ions are unavoidable in the aqueous medium, therefore, we need a catalyst which can competitively reduce CO2 over H2 evolution. The CPE analysis using protein PBSE-CNT composite resulted ~ 50% faradaic efficiency (FE) for CO2 to CO, ~20% FE for CO2 to CH4 and the remaining H2. But the production of H2 can be accounted from the control (PBSE-CNT) CPE which was 30 times more than that produced by the protein PBSE CNT composite.

Designed metalloproteins for efficient CO2 reduction via low valent Fe (I/0) state in aqueous medium

255th National Meeting (2018)

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