Electroreduction of CO2 Catalyzed by Nickel Imidazolin-2-ylidenamino-Porphyrins in Both Heterogeneous and Homogeneous Molecular Systems

Electrocatalytic carbon dioxide reduction to value-added chemicals is an important strategy to store renewable energy. Despite recent advances, the current level of performance of these systems does not justify the projected expenses of their commercial applications. Efforts to attain benchmark reaction rates and long-term operational stability are being addressed through the design of tunable molecule-based electrocatalysts. In this project, we synthesized a new class of 1,3-ditert-butylimidazolin-2-ylidenamino (NItBu) nickel porphyrin and evaluated its ability to reduce CO2 to CO. The presence of these strong, electron-rich donors efficiently directed electron density to the metal center and resulted in Faradaic efficiency of 62% and current density of -2 mA/cm(2) at -1.1 V versus reference hydrogen electrode (RHE) in homogeneous media. Following noncovalent immobilization of these compounds onto carbon nanotubes (CNTs), we could further dramatically enhance the product selectivity to 94% and catalytic activity to -22 mA/cm(2) at much more positive potentials of -0.5 V versus RHE. We believe that this systematic study of electron-rich substituted nickel porphyrins will provide valuable insights into the intricate relationship between catalytic performance and molecular structure that will inspire new forays into the development of catalytic systems for electrochemical CO2 reduction.