| Details: |
The development of new technology that can capture and/or convert CO2 to other products is of great interest. Such approaches are promising for addressing concerns about curbing greenhouse gas emissions and finding alternative sources of chemical fuels and feedstocks (e.g., hydrocarbons). Research on the conversion of CO2 to CO has been re-intensified in the last decade, but robust catalysts that can carry out the CO2 reduction reaction (CO2RR) with good kinetics parameters are still being developed. One of the challenges for the selective reduction is the precise input of multiple protons (H+) and electrons (e–). Recently, we have published that the iron-porphyrin systems bearing three phenyl groups at the meso- positions, and a proton relay group at the remaining meso- position are more robust heterogeneous catalysts for O2 reduction (another example of multi-H+/ e– reaction). Being inspired by this work, we design similar frameworks for electrocatlytic CO2 reduction. We have optimized the synthesis of ligand, 5-hydroxophenyl-10,15,20-triphenylporphyrin (TPOH) and synthesized a series of metalloporphyrins (MTPOH) using the first row transition metals (MnII, FeIII, CoII, NiII, CuII). Electrochemically-generated Fe0TPOH behaves as the best homogeneous catalyst for CO2 reduction in CO2-saturated 0.1 nBu4NPF6 acetonitrile (Ecat = –2.1 V vs. Cp2Fe+/0). Notably, the addition of 1 M H2O improved the catalytic current densities by ~100-fold. Investigation of the minimum requirement for number of proton relay groups at the meso-position(s) of metalloporphyrins are ongoing. |