Electrocatalytic Activation of CO2 and its Applications

Chakrabarti, Navonil (2025) Electrocatalytic Activation of CO2 and its Applications. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Navonil Chakrabarti (21MS167)) 21MS167_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

Despite urea being an essential source of nitrogen for plants in a world with rising demands for food & agriculture, the only commercial source involves the Bazarov reaction, where carbon dioxide (CO2) and ammonia (NH3) are reacted under high temperatures and pressure notwithstanding the use of NH3 which finds it’s source in the equally energy-intensive Haber-Bosch process. This stepwise reaction makes this process highly energy-demanding. Electrocatalytic urea formation using CO2 and N2 via 6e- transfer (N2 + CO2 + 6e- + 6H+ → CO(NH2)2 + H2O) is a viable alternative, but has only been previously explored heterogeneously. Consequently, the intermediates involved and the overall mechanism still prove elusive. The electrochemical reduction of N2 and CO2 at ambient conditions using a homogeneous metal complex is yet to be achieved. The key considerations for achieving this feat homogenously include CO2 and N2 reduction within the same potential range, enabling the formation of the C-N bond while minimizing hydrogen evolution reactions (HER). Recently, our group explored the electrocatalytic reduction of N2 using a Co(III) catalyst, CoNDPA(Py)₂ (1), where we observed the selective production of hydrazine (N2H4) at potentials close to ~ -1.6 V (Fc+/Fc). As elucidated in the latter portion of this work, we observe electrocatalytic CO2 reduction at similar potentials, which, alongside N2 reduction, shows minimum H2 evolution, making 1 suitable for electrocatalytic urea formation using CO2 and N2 via 6e- transfer. We envisioned that using complex 1 for the simultaneous reduction of CO2 and N2 could lead to C-N coupled products. Herein, we report a well-characterized CO2 reduction cycle with detailed mechanistic analysis both via theoretical analysis and spectroscopy. We also report, to the best of our knowledge, the first homogenous electro-catalyzed urea formation via a hitherto unobserved dual gas activation by a Co(III) complex, CoNDPA(Py)2 (1) in a 1:4 (v/v) H2O: ACN mixture with yields no less than previous reports of heterogeneously electro-catalyzed N-N bond cleavages of N2H4 in the presence of CO2.

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