Surface Amorphization of Bismuth for Efficient Acidic CO₂ Electrolysis

The electrochemical conversion of CO 2 into valuable chemicals under acidic conditions provides a promising solution to challenges, such as carbon loss and catalyst instability caused by carbonate precipitation. However, acidic CO 2 electroreduction remains severely constrained by intense competition from the hydrogen evolution reaction (HER) and sluggish CO 2 activation kinetics. Here, we report a bismuth (Bi) nanoparticle catalyst with an amorphous surface layer ( a -Bi), which demonstrates high catalytic activity and selectivity toward formic acid (HCOOH) formation in acidic electrolytes. The catalyst achieves impressive Faradaic efficiencies for HCOOH production, exceeding 90% over a wide current density range (−100 to −1000 mA cm –2 ) with corresponding potentials ranging from −1.24 to −1.75 V versus the reversible hydrogen electrode (vs RHE). Notably, the partial current density for an HCOOH reaches an impressive value of more than −900 mA cm –2 at −1.75 V vs RHE. Furthermore, the a -Bi catalyst exhibited stability for over 52 h at high production rates (−500 mA cm –2 ) alongside a single-pass carbon efficiency of approximately 85%. In situ spectroscopy and theoretical simulation revealed that surface amorphization significantly enhances the adsorption of CO 2 and lowers the hydrogenation barrier, thereby accelerating the CO 2 RR kinetics while effectively suppressing the HER. This work presents a facile crystallization engineering strategy to address critical carbon loss challenges, thereby advancing the sustainability and scalability of acidic CO 2 electroreduction processes.