Bifurcation of *COOH Pathway Determines HCOOH Formation in CO₂ Electroreduction on Bismuth

Bismuth (Bi) is a promising electrocatalyst for the CO₂ reduction reaction (CO₂RR) to formic acid (HCOOH), yet its mechanism remains a subject of debate. While the pathway involving the oxygen-bound *OCHO intermediate is conventionally accepted, experimentally observed carbon-bound species have been largely overlooked. In this work, we resolve this mechanistic ambiguity by combining constant-potential ab initio molecular dynamics (AIMD) simulations with spectroscopic evidence. We reveal that the reaction on Bi is governed by the bifurcation of the *COOH pathway, which favors HCOOH formation over CO. We also identify an *H-mediated pathway as an alternative route at low potentials where *CO₂ activation is suppressed. Supported by the experimental detection of *COOH, our findings suggest that this mechanism is likely a general feature across other metal surfaces, such as Ag, Cu, and In. Consequently, we bring the *COOH-mediated mechanism to the forefront of HCOOH production, highlighting the need to consider this pathway in the rational design of future HCOOH-selective electrocatalysts.