Improving the electrocatalytic CO2 reduction performance of Bi catalysts for formic acid production via size control, morphology regulation and carbon complexation

Abstract

The electrocatalytic carbon dioxide reduction reaction (CO₂RR) is considered as a promising approach for simultaneous CO₂ treatment and production of value-added chemicals. Bismuth has been demonstrated as a fascinating electrocatalyst for selective conversion of CO₂ to HCOOH. In this study, we comprehensively investigated the effects of size, morphology, and carbon supports on the CO₂RR performance of Bi catalysts to enhance their electrocatalytic CO₂RR activity and HCOOH selectivity. Specifically, Bi nanospheres with varying sizes were synthesized by adjusting the amount of polyvinylpyrrolidone (PVP), achieving similar selectivity for HCOOH but increasing current density with decreasing size. Bi nanoplates and Bi nanoflowers were also prepared through the reduction of BiOCl precursors, with Bi nanoflowers demonstrating a superior morphology compared to other Bi nanocrystals while achieving a HCOOH faradaic efficiency (FE_HCOOH) of 95% at −1.6 V vs. SCE and excellent durability over 12 hours. The predominance of *HCOO intermediates in the in situ ATR-SEIRA spectra indicates that during the CO₂RR, Bi nanoflowers primarily followed the pathway leading to HCOOH production. Furthermore, incorporation of Ketjenblack into the synthesis process resulted in carbon-supported Bi catalysts, which exhibited approximately 20% enhancement in FE_HCOOH within a wide potential range from −1.3 V to −1.8 V vs. SCE due to an improved separation effect and electron transfer capacity provided by carbon materials.