Ultrathin N,S-Codoped Bi ₂ O ₃ Nanosheets for High-Selectivity CO ₂ Electroreduction to Formate via Electronic Structure Modulation

Simultaneously achieving high active-site density, rapid interfacial charge transfer, and robust structural stability remains a major challenge in Bi-based electrocatalysts for the electroreduction of CO 2 to formate. Herein, ultrathin N,S-codoped Bi 2 O 3 nanosheets (N,S–Bi 2 O 3 ) were synthesized through a solvothermal-calcination strategy to engineer the local electronic structure of Bi centers and accelerate eCO 2 RR kinetics. The optimized catalyst affords a maximum formate faradaic efficiency (FE formate ) of 99.1% at −0.91 V vs RHE together with a mass-normalized formate current density ( j mass,formate ) of −246 mA mg –1 . Moreover, FE formate remains above 93% over a potential window wider than 400 mV, while the catalyst exhibits stable long-term operation. Experimental analyses combined with DFT calculations reveal that N/S codoping facilitates CO 2 activation, reinforces adsorption of the key *OCHO intermediate, and lowers the energy barrier for the formate pathway. These results demonstrate that coupling an ultrathin nanosheet architecture with dual-heteroatom electronic modulation is an effective route to high-performance Bi-based electrocatalysts for selective CO 2 electroreduction.