<i>In situ</i> reconstructed vacancy confined in Bi nanosheets enabling high-selective CO ₂ electroreduction to formate at industrial-current-density

Electroreduction derived Bi-based materials have been recognized as promising catalysts for CO₂ reduction to formate, however, it remains unclear whether the reconstructed Bi vacancies significantly influence the reaction performance. Herein, we first construct vacancies-rich Bi nanosheets through an in situ electroreduction process, in which positron annihilation lifetime spectroscopy unravels the&nbsp;presence&nbsp;of&nbsp;Bi&nbsp;monovacancy states, confirmed by in situ Raman spectra. In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy and operando Raman spectra unravel the Bi vacancies could enhance the adsorption of *OCHO key intermediates and facilitate their reaction kinetics. Moreover, density-functional-theory calculations demonstrate the Bi vacancies induce electron aggregation, thereby stabilizing the *OCHO intermediates. As a result, the Bi nanosheets with abundant vacancies achieve a remarkable formate Faradaic efficiency of 97.1% at current density of 200 mA cm⁻², and produce 1 M pure formic acid solution for 250 hours in a solid electrolyte reactor.