Residual iodine on in-situ transformed bismuth nanosheets induced activity difference in CO2 electroreduction

Bismuth oxyhalides are prone to be transformed to bismuth metal in electroreduction and the halogen effects on the in-situ transformed bismuth metal for electroreduction of CO2 (ECO2RR) are worth exploring. In this work, Bi4O5Cl2, Bi4O5Br2 and BiOI nanosheets used as pre-catalysts were synthesized by electrochemical exfoliation method to explore the effect of residual halogen on ECO2RR performance. The XPS analysis and theoretical model of bismuth oxyhalides transformed Bi disclose that the sandwich structure and high percent composition of I atoms in BiOI crystal lattice are the key factors for the presence of residual I. The residual I was previously reported to interact with CO2 via the electron flow, constraining CO2 around the electrode and accelerating the charge transfer to CO2, thus exhibiting the excellent activity of BiOI in-situ transformed Bi nanosheets compared with Bi4O5Br2 and Bi4O5Cl2 in-situ transformed Bi nanosheets. This work may stimulate more attention on the effect of in-situ formation of halogen in ECO2RR.