A stability strategy for doped modified bismuth sulfide in CO₂RR for reducing CO₂ to HCOOH

The electrochemical carbon dioxide reduction reaction (CO₂RR) offers a promising approach to convert CO₂ into high-value chemical while mitigating emission and utilizing of carbon resources efficiently. In this paper, we presented an effective approach using bismuth sulfide (Bi₂S₃) catalyst for CO₂RR, achieving selective and stable formic acid (HCOOH). Over a broad voltage range -0.6 to -1.4 V vs. reversible hydrogen electrode (RHE), the Faraday efficiency (FE) of HCOOH remained consistently above 95 %, with a peak FE of 96 % at -1.3 V vs. RHE, accompanied by a peak partial current density (j_HCOOH) of -304 mA/cm². Stability tests demonstrated a minimal FE decline and only a 7 % drop in current density after 10 h, attributed to inevitable flushing effects in the flow-cell. Under hydrothermal synthesis conditions, systematic investigations revealed that increased temperature and optimized sulfur content induced a morphological transformation from nanorods to nanosheets, as observed via electron microscopy. This structural evolution enhanced both FE and stability across a broad voltage range. In-situ spectroscopy and experimental analysis further indicated that sulfur doping modulated the electronic structure of bismuth, promoting the formation of the key intermediate HCOO* and facilitating HCOOH production. This work demonstrates an efficient and durable electrocatalyst for sustainable HCOOH synthesis.