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

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).

Abstract

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.

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