Electrochemical conversion of CO2 to C2 oxygenates on Pb(II)-salen catalysts-coated graphite electrodes: Role of salen ligand and appended ligand-substituents to the production

[Display omitted] •Three Pb(II)-salen complexes synthesized by metalation reaction in presence of Et3N.•Pb-salen complexes showed better CO2 conversion efficiency than pure PbO.•–NH2 in Pb(II)-salen ligand increased availability of CO2/CO for multiple products.•FE of 57% and 36% achieved for ethanol and acetic acid for Complex 2 and Complex 3. Electrochemical reduction of CO2 (ERC) generates higher-value and higher-energy density multicarbon C1+ products that serve as alternatives to fossil fuels and feedstocks for the chemical industries. Herein, we uncover three Pb(II)-salen complexes (1 = [PbII(LH)]0, 2 = [PbII(LNO2)]0, and 3 = [PbII(LNH2)]0) as the catalysts that were deposited onto graphite electrodes to fabricate working electrodes. In complex 1, no functional groups were incorporated in the parent H2LH ligand backbone, while, a –NO2 and an –NH2 functional groups were present in the ligand frameworks in complex 2 and complex 3, respectively. The ERC by complex 1-coated graphite electrode generated only C1 products, formic acid (HCOOH, FE = 7%; SE = 41%), and methanol (CH3OH, FE = 28%; SE = 59%) at −1.80 V vs. Ag/AgCl, at pH ∼ 7.0. However, ERC under the same condition employing complex 2 and complex 3 as electrocatalysts, C2 products formation predominated. While, ethanol (CH3CH2OH) was formed as the major C2 product with FE = 57%, SE = 66% and TON (TOF) = 31680 (8.8 s−1) in the presence of complex 2, mainly acetic acid (CH3COOH, FE = 36%; SE = 54%) with overall product FE = 67% was realized using complex 3 as the electrocatalyst. Thus, the presence of functional groups facilitated C–C coupling between the pertinent intermediates. The role of the ligand frameworks was to modify the substrate and/or proton concentrations over the electrode surfaces for the successive reduction of CO2 to oxygenates.