CO2-to-HCOOH electrolysis on intercalation-engineered bismuth-oxybromide with self-renewing hydroxyls

Electrocatalytic CO2 reduction is one of the most promising ways to mitigate global warming and energy crisis. BiOBr nanosheets with preferentially exposed facet (0 1 0) was well-fabricated to facilitate formate electrosynthesis, which achieved stable output at ultra-wide voltage window of 1200 mV, and the Faraday efficiency of formate was 96.9 % at −0.7 V vs. RHE. Compared to BiOBr (0 0 1), BiOBr (0 1 0) can promote water-splitting and produce hydroxyls (*OH). The orderly arrangement of [Bi2O2]2+/[Br]− layers and larger [Bi2O2]2+ layer spacing over the (0 1 0) facet promotes the *OH diffusion to the interlayer and then combining with CO2 to form Bi2O2CO3 intermediates. It finally converts to hydroxyls-contained metallic bismuth after electroreduction. These hydroxyls are proved to be self-renewable to launch a new round of BiOBr-to-Bi2O2CO3-to-active bismuth progress, which promote the activation of CO2 thermodynamically and maintain the stability of operation continuously. The intercalation-engineered strategy overcomes the uncontrollability of electrochemical reconstruction and realize target-regulation of active sites.