Engineering Single‐Atom Sites with the Irving–Williams Series for the Simultaneous Co‐photocatalytic CO2 Reduction and CH3CHO Oxidation

The bonding effects between 3d transition‐metal single sites and supports originate from crystal field stabilization energy (CFSE). The 3d transition‐metal atoms of the spontaneous geometrical distortions, that is the Jahn–Teller effect, can alter CFSE, thereby leading to the Irving–Williams series. However, engineering single‐atom sites (SASs) using the Irving–Williams series as an ideal guideline has not been reported to date. Herein, alkynyl‐linked covalent phenanthroline frameworks (CPFs) with phenanthroline units are developed to anchor the desired 3d single metal ions from d5 to d10 (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+). The Irving–Williams series was employed to accurately predict the bonding effects between 3d transition‐metal atoms and phenanthroline units. To verify this, theoretical calculations and experimental results reveal that Cu‐SASs/CPFs exhibits higher stability and faster charge‐transfer efficiency, far surpassing other metal‐SASs/CPFs. As expected, Cu‐SASs/CPFs demonstrates a high photoreduction of CO2‐to‐CO activity (~30.3 μmol ⋅ g−1 ⋅ h−1) and an exceptional photooxidation of CH3CHO‐to‐CH3COOH activity (~24.7 μmol ⋅ g−1 ⋅ h−1). Interestingly, the generated *O2− is derived from the process of CO2 reduction, thereby triggering a CH3CHO oxidation reaction. This work provides a novel design concept for designing SASs by the Irving–Williams to regulate the catalytic performances. In order to engineer single‐atom sites from d5 to d10, the Irving–Williams series was employed to accurately predict the highest stability and fastest charge‐transfer efficiency. As predicted, Cu‐SASs/CPFs exhibits a higher activity towards the photoreduction of CO2‐to‐CO and the photooxidation of CH3CHO‐to‐CH3COOH, far surpassing other metal‐SASs/CPFs.