Reordering d Orbital Energies of Single-Site Catalysts for CO2 Electroreduction.

The single-site catalyst (SSC) characteristic of atomically dispersed active centers will not only maximize the catalytic activity, but also provide a promising platform for establishing the structure-activity relationship. However, arbitrary arrangements of active sites in the existed SSCs make it difficult for mechanism understanding and performance optimization. Now, a well-defined ultrathin SSC is fabricated by assembly of metal-porphyrin molecules, which enables the precise identification of the active sites for d-orbital energy engineering. The activity of as-assembled products for electrocatalytic CO2 reduction is significantly promoted via lifting up the energy level of metal d z 2 orbitals, exhibiting a remarkable Faradaic efficiency of 96 % at the overpotential of 500 mV. Furthermore, a turnover frequency of 4.21 s-1 is achieved with negligible decay over 48 h.