Unveiling the enhanced electrochemical CO2 conversion: The role of 3D porous BiOCl with defects and CTAB-mediated nanosheets

A 3D flower-like structure composed of porous bismuth oxychloride (p-BiOCl) nanosheets was synthesized through a hydrothermal process utilizing Bi(NO₃)₃･5 H₂O, cetyltrimethylammonium bromide (CTAB) and LiCl. Powder X-ray diffraction (PXRD) studies confirmed the successful formation of the p-BiOCl. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were exploited to identify the nanosheet structure. The catalyst appeared as reduced Bi⁰ nanosheets at an applied cathodic potential of − 0.92 V (vs. RHE (reversible hydrogen electrode)). The maintenance of Bi nanosheet structures, controlled by the cationic surfactant of CTAB, resulted in enhanced electrochemical activity with a favorable Tafel slope and lower charge resistance. Defects of under-coordinated Bi sites and oxygen vacancy with interconnected 3D structures possess abundant active sites that further assist the activity. In 1.0 and 2.0 M KHCO₃ electrolytes, the catalyst achieved a maximum current density of − 80 and 100 mA/cm², respectively, at − 0.92 V (vs. RHE) with Faradaic efficiency > 99 % for converting CO₂ to formate in H-cell electrolyzers. The substantial H/D kinetic isotope effect revealed from H₂O versus D₂O electrolytes, and the feature of bicarbonate concentration-dependent performance provided the mechanistic insights that bicarbonate intermediates are in equilibrium with CO₂, activated by water, in the aqueous environment, together with the effects of electrode surface modulated by CTAB, are essential for the efficient electrochemical CO₂ reduction reaction to formate.