Surface Amorphization of Bismuth for Efficient Acidic CO2 Electrolysis

The electrochemical conversion of CO2 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 CO2 electroreduction remains severely constrained by intense competition from the hydrogen evolution reaction (HER) and sluggish CO2 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 CO2 and lowers the hydrogenation barrier, thereby accelerating the CO2RR 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 CO2 electroreduction processes.