Crown-Ether-Modified Bismuth Nanorods for Highly Efficient and Stable CO₂ Electroreduction to Formic Acid in a Locally Acidic Environment

Implementing the CO 2 reduction reaction (CO 2 RR) in acidic environments is often obstructed by diminished product selectivity resulting from the competing hydrogen evolution reaction (HER). This work unveils a highly effective strategy of using carbon-supported bismuth nanorods (Bi-NRs/C) adorned with crown ethers (15-Crown-5, 18-Crown-6, Dibenzo-18-Crown-6, and Dibenzo-21-Crown-7) to facilitate selective and durable formic acid synthesis in highly acidic electrolytes (pH = 1). The crown-ether-modified electrodes promote the accumulation of alkali metal cations (Na +, K +, and Cs + ) near the Bi-NRs/C catalyst surface, enhancing the interfacial electric field to stabilize CO 2 RR intermediates and inhibiting HER. This synergistic effect boosts the CO 2 RR to formic acid with a faradaic efficiency (FE) ≥ 94% for the best performance of Bi-3 C6 (i.e., the molar ratio of Bi to 18-Crown-6 is 3) systems. Moreover, the catalyst demonstrates exceptional long-term stability over 72 h of uninterrupted electrolysis without any sign of deterioration. This study highlights the promise of CO 2 RR catalyst modification through crown ether adsorption and establishes a flexible framework of supramolecular interaction for developing resilient and effective catalysts for the CO 2 RR in strongly acidic media.