Asymmetric Ni single-atom sites from bio-MOF-1 enable spin-state modulation for highly efficient CO2 electroreduction

Abstract

Asymmetric coordination environments in single-atom catalysts (SACs) offer an effective means to modulate spin states and improve catalytic performance in the electrochemical CO2 reduction reaction (CO2RR). However, fabricating such low-symmetry sites remains synthetically challenging. Here, we report a Ni-based SAC (n-Ni-BMF-N-C) featuring a three-dimensional asymmetric Ni–N3+1–O coordination motif, engineered via tailored MOF architecture (bio-MOF-1) and TEA-mediated structural modulation. This asymmetric coordination environment effectively reconfigures the 3d orbital occupancy of the Ni center, favoring a high-spin electronic state that enhances metal–adsorbate interactions. This reconfiguration notably redistributes the Ni 3d orbital manifold to enable multi-orbital interaction with the *COOH intermediate, facilitating its stabilization and reducing the thermodynamic penalty for the rate-determining *COOH formation step. Such orbital alignment translates into exceptional catalytic performance, with n-Ni-BMF-N-C achieving ∼99% CO Faradaic efficiency at −1.1 V and sustaining > 92% selectivity across a wide potential window—underscoring its status as one of the most selective M–N–C systems for CO2-to-CO conversion. The catalyst further demonstrates superior mass-transport properties in a flow-cell, sustaining > 95.5% CO selectivity at current densities exceeding 160 mA cm−2. The practical applicability of the catalyst is further demonstrated by its integration into a Zn–CO2 battery, where it delivers a peak power density of 0.94 mW cm−2 and a maximum FECO of 92.9%, along with stable operation over 50 h, demonstrating excellent device-level viability. These results establish asymmetric spin-state engineering as a powerful strategy for creating efficient and durable SACs with strong potential for scalable CO2-to-CO conversion in energy applications.