Bismuth is a catalyst material that selectively produces
formate
during the electrochemical reduction of CO2. While different
synthesis strategies have been employed to create electrocatalysts
with better performance, the restructuring of bismuth precatalysts
during the reaction has also been previously reported. The mechanism
behind the change has, however, remained unclear. Here, we show that
Bi2O3 nanoparticles supported on Vulcan carbon
intrinsically transform into stellated nanosheet aggregates upon exposure
to an electrolyte. Liquid cell transmission electron microscopy observations
first revealed the gradual restructuring of the nanoparticles into
nanosheets in the presence of 0.1 M KHCO3 without an applied
potential. Our experiments also associated the restructuring with
solubility of bismuth in the electrolyte. While the consequent agglomerates
were stable under moderate negative potentials (−0.3 VRHE), they dissolved over time at larger negative potentials
(−0.4 and −0.5 VRHE). Operando Raman spectra collected during the reaction showed that under an
applied potential, the oxide particles reduced to metallic bismuth,
thereby confirming the metal as the working phase for producing formate.
These results inform us about the working morphology of these electrocatalysts
and their formation and degradation mechanisms.