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 (<i>a</i>-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 <i>a</i>-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%. <i>In situ</i> 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.