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

Abstract

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.

Keywords

• Bismuth
• CO2 reduction
• Defects
• Formate
• Porous bismuth oxychloride
• X-ray absorption spectroscopy