Insertion of Indium on Bismuth Sulfide Nanorod Embedded on Graphitic Carbon Nitride for Enhanced Selectivity Toward Formate in Electrochemical CO ₂ Reduction

Electrochemical CO 2 reduction (ECO 2 R) to formate is attractive due to its industrial relevance, low electron transfer requirement, and potential for scalable renewable fuel production. However, conventional post-transition metal catalysts often require high overpotentials and exhibit limited activity at elevated current densities. Here, we report the design of indium-doped Bi 2 S 3 nanorods embedded in graphitic carbon nitride (In X Bi 2 S 3 G), which integrate the favorable oxygen affinity of Bi with electronic modulation from In and enhanced CO 2 adsorption on g-C 3 N 4 . The optimized In3 Bi 2 S 3 G catalyst achieves ≈94% Faradaic efficiency for formate with a partial current density of 85.1 mA cm –2 in a flow cell, delivering a cathodic energy efficiency of 18.2% at −1.03 V vs RHE and sustaining operation for over 60 h. DFT and electrochemical analyses revealed that In incorporation tunes *OCHO binding while suppressing hydrogen evolution, whereas g-C 3 N 4 provides a conductive and CO 2 -affinitive scaffold. This work establishes In X Bi 2 S 3 G as a robust and efficient platform for selective ECO 2 R to formate conversion under industrially relevant conditions.