Promoting the Electrocatalytic Reduction of CO2 on Ultrathin Porous Bismuth Nanosheets with Tunable Surface-Active Sites and Local pH Environments

Electrochemical CO₂ reduction reaction (CO₂RR) yielding value-added chemicals provides a sustainable approach for renewable energy storage and conversion. Bismuth-based catalysts prove to be promising candidates for converting CO₂ and water into formate but still suffer from poor selectivity and activity and/or sluggish kinetics. Here, we report that ultrathin porous Bi nanosheets (Bi-PNS) can be prepared through a controlled solvothermal protocol. Compared with smooth Bi nanoparticles (Bi-NPs), the ultrathin, rough, and porous Bi-PNS provide more active sites with higher intrinsic reactivities for CO₂RR. Moreover, such high activity further increases the local pH in the vicinity of the catalyst surfaces during electrolysis and thus suppresses the competing hydrogen evolution reaction. As a result, the Bi-PNS exhibit significantly boosted CO₂RR properties, showing a Faradaic efficiency of 95% with an effective current density of 45 mA cm^-2 for formate evolution at the potential of -1.0 V versus reversible hydrogen electrode.