Uncovering the nature of electroactive sites in nano architectured dendritic Bi for highly efficient CO2 electroreduction to formate

Porous electrodes based on Bismuth dendrites (Biden) were fabricated using Dynamic Hydrogen Bubbling Templates (DHBT). Direct visualization of surface-active sites with the help of advanced transmission electron microscopic (TEM) imaging reveals the presence of abundant defect structures and high-index faceting, while selective decoration of low-index facets of Bi dendrites indicate that they are the most active Bi surface sites. The fabricated electrodes show high selectivity toward CO2 electroreduction to formate synthesis, with a 98% Faradaic Efficiency and a current density of 18.8 mA cm−2 (344 μmol cm−2 h–1) at –0.82 V vs RHE, which is only 600 mV more negative than the thermodynamic potential. Both the dendritic structure and CO2 electrolysis performances are remarkably stable over long electrolysis periods (∼15 h). Additionally, large production rates (1.63 mmol cm−2 h–1 or 95 mA cm−2 at –0.82 V vs RHE) without significant penalty on the formate Faradaic Efficiency (92 ± 4%) was achieved in high-pressure flow cell, where the CO2 flux is greatly enhanced compare to an H-cell. The work thus outlines an effective strategy for the development of dendritic materials with superior performance toward electroreduction of CO2.