Evolution of bismuth electrodes activating electrosynthesis of formate from carbon dioxide reduction

Electrochemical conversion of CO2 into valuable chemicals and fuels has emerged as a promising approach to achieving the net-zero emission target. In this work, bismuth (Bi)-based gas diffusion electrodes (GDEs) are prepared via scalable inkjet printing of the precursor on carbon papers, and subsequent thermal treatment. The optimization of the GDEs aims at the efficient CO2 reduction to formate (HCOO-) with good selectivity and high current density. Ex situ FESEM, XRD, and XPS analyses evidence the morphological and structural transformations of Bi-based catalysts during electrolysis. In situ Raman spectroscopy illustrates the dynamic evolution of the electrocatalysts in a range of potentials. The complete procedure is represented as the transformation of Bi2O3 polyhedral microcrystals to a flower-like assembly of Bi2O2CO3 nanoflakes when exposed to KHCO3 electrolyte under electrochemical conditions, and then to metallic Bi at more negative potentials (< -0.6 V vs. RHE). The evolution of Bi-GDEs confirms that metallic Bi nanostructure provides abundant active sites for selective conversion of CO2 to HCOO-, and is highly promising for applications at industrially relavant scales.