Continuous electroproduction of formate via CO2 reduction on local symmetry-broken single-atom catalysts

Atomic-level coordination engineering is an efficient strategy for tuning the catalytic performance of single-atom catalysts (SACs). However, their rational design has so far been plagued by the lack of a universal correlation between the coordination symmetry and catalytic properties. Herein, we synthesised planar-symmetry-broken CuN3 (PSB-CuN3) SACs through microwave heating for electrocatalytic CO2 reduction. Remarkably, the as-prepared catalysts exhibited a selectivity of 94.3% towards formate at -0.73 V vs. RHE, surpassing the symmetrical CuN4 catalyst (72.4% at -0.93 V vs. RHE). In a flow cell equipped with a PSB-CuN3 electrode, over 90% formate selectivity was maintained at an average current density of 94.4 mA cm-2 during 100 h operation. By combining definitive structural identification with operando X-ray spectroscopy and theoretical calculations, we revealed that the intrinsic local symmetry breaking from planar D4h configuration induces an unconventional dsp hybridisation, and thus a strong correlation between the catalytic activity and microenvironment of metal centre (i.e., coordination number and distortion), with high preference for formate production in CuN3 moiety. The finding opens an avenue for designing efficient SACs with specific local symmetries for selective electrocatalysis.