A stability strategy for doped modified bismuth sulfide in CORR for reducing CO to HCOOH.

The electrochemical carbon dioxide reduction reaction (CORR) offers a promising approach to convert CO into high-value chemical while mitigating emission and utilizing of carbon resources efficiently. In this paper, we presented an effective approach using bismuth sulfide (BiS) catalyst for CORR, 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) of -304 mA/cm. 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.