Spin Manipulation in a Metal–Organic Layer through Mechanical Exfoliation for Highly Selective CO2 Photoreduction

Spin manipulation of transition‐metal catalysts has great potential in mimicking enzyme electronic structures to improve activity and/or selectivity. However, it remains a great challenge to manipulate room‐temperature spin state of catalytic centers. Herein, we report a mechanical exfoliation strategy to in situ induce partial spin crossover from high‐spin (s=5/2) to low‐spin (s=1/2) of the ferric center. Due to spin transition of catalytic center, mixed‐spin catalyst exhibits a high CO yield of 19.7 mmol g−1 with selectivity of 91.6 %, much superior to that of high‐spin bulk counterpart (50 % selectivity). Density functional theory calculations reveal that low‐spin 3d‐orbital electronic configuration performs a key function in promoting CO2 adsorption and reducing activation barrier. Hence, the spin manipulation highlights a new insight into designing highly efficient biomimetic catalysts via optimizing spin state. The manipulation of Fe3+ spin states from high spin (HS; s=5/2) in bulk crystals to mixed spin lattices (with s=5/2 and low spin (LS); s=1/2) is demonstrated in a two‐dimensional ultrathin metal–organic layer catalyst by mechanical exfoliation. The resulting catalyst has enhanced activity and selectivity for CO2 photoreduction (CO2RR) over the hydrogen evolution reaction (HER).