Tailored Local Electronic Environment of Co‐N4 Sites in Cobalt Phthalocyanines for Enhanced CO2 Reduction Reaction

Atomically dispersed Co-N₄-based catalysts have been recently emerging as one of the most promising candidates for facilitating CO₂ reduction reaction (CO₂RR). The local electronic environment of Co-N₄ sites in these catalysts is considered to play a critical role in adjusting the catalytic performance, the effort of which however is not yet clearly verified. Herein, a series of cobalt phthalocyanines with different peripheral substituents including unsubstituted phthalocyanine Co(II) (CoPc), 2,9,16,23-tetramethoxyphthalocyaninato Co(II) (CoPc-4OCH₃), and 2,9,16,23-tetranitrophthalocyaninato Co(II) (CoPc-4NO₂) are supported onto the surface of the multi-walled carbon nanotubes (CNTs), affording CoPc@CNTs, CoPc-4OCH₃@CNTs, and CoPc-4NO₂@CNTs. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure measurements disclose the influence of the peripheral substituents on the local electronic structure of Co atoms in these three catalysts. Electrochemical tests indicate the higher CO₂RR performance of CoPc-4OCH₃@CNTs compared to CoPc@CNTs and CoPc-4NO₂@CNTs as exemplified by the higher Faraday efficiency of CO, larger part current densities, and better stability displayed by CoPc-4OCH₃@CNTs at the applied voltage range from -0.6 to -1.0 V versus RHE in both H-cell and flow cell. These results highlight the effect of the electron-donating -OCH₃ substituent on the enhanced catalytic activity of CoPc-4OCH₃@CNTs, which will help develop Co-N₄-based catalysts with promising catalytic performance toward CO₂RR.