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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 (FEHCOOH) 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 FEHCOOH 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. [ABSTRACT FROM AUTHOR]