Enhanced electron delocalization induced by p-p-d orbital coupling for high-rate formic acid electrosynthesis

The electroreduction of carbon dioxide (CO₂RR) to high-value-added formic acid (HCOOH) is of great significance for closing the anthropogenic CO₂ cycle. Bismuth oxide (Bi₂O₃) possesses Bi^δ+ sites that is favorable for oxygenate intermediate (i.e. *OCHO) adsorption, while the competitive hydrogen evolution reaction is also facilitated, inhibiting broad-range high selectivity. In this work, we propose to build an ultrathin Bi₂WO₆ nanosheets (NSs) with Aurivillius-phase for enhancing electronic delocalization of Bi^δ+ by 5d (Bi)−2p (O)−6p (W) orbital coupling. The delocalized Bi^δ+ sites could boost the coupling between the O 2p orbital of *OCHO and the Bi 6p orbital that promotes *OCHO adsorption and electron transfer from Bi^δ+ to the *OCHO intermediate, thereby improving the CO₂RR performance and maintaining structure. In situ Raman spectroscopy and theoretical calculations demonstrated that delocalized Bi^δ+ could optimize the structure of interfacial water and decrease the *H coverage for restraining by-product H₂ production. As a result, these advantages endowed the Bi₂WO₆ NSs with high HCOOH selectivity of 97.8% and peak partial current density of 877 mA cm^–2, superior to pristine Bi₂O₃ and Aurivillius-phase bismuth molybdate NSs.