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Unveiling the Origin of pH-Dependent Catalytic Performance of Bi2O3 Nanostructure for Electrochemical CO2 Reduction

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Over the past decade, the electrochemical conversion of CO 2 into valuable chemicals and fuels has garnered increasing interest as a promising pathway toward a carbon-neutral circular economy. This study investigates Bi 2 O 3 gas diffusion electrodes (Bi-GDEs) for the conversion of CO 2 to formic acid/formate (HCOOH/HCOO – ), which demonstrate excellent selectivity at high current densities. The catalyst is synthesized through a one-pot microwave-assisted process that is rapid, energy-efficient, and scalable, utilizing the green solvent ethylene glycol. The resulting Bi 2 O 3 nanostructure achieves near-unit selectivity for CO 2 conversion, with a faradaic efficiency exceeding 95% for HCOOH/HCOO – formation across a wide pH range. The catalytic activity is strongly pH-dependent, with an increase in the pH reducing the overpotential at a given current density. To elucidate the origin of this pH-dependent activity, operando Raman spectroscopy, post-mortem scanning electron microscopy (SEM), and electrical double layer characterization were performed. Operando Raman results reveal that Bi 2 O 3 undergoes reduction more readily in highly acidic or basic electrolytes, whereas its reduction is inhibited near neutral pH. However, at highly negative potentials relevant to CO 2 RR, cationic Bi species fully convert to metallic Bi. Despite structural variations at different electrolyte pH values, metallic Bi remains the active phase, explaining the high selectivity of Bi-GDEs across a broad pH range. Post-mortem SEM images highlight the influence of electrolyte pH on morphological evolution under CO 2 RR conditions. At the highest pH of 14, a hierarchical dendritic structure emerges, showing an increase of 100% in double layer capacitance, which evidences the significant enhancement in the electrochemical active surface area and consequently the CO 2 RR activity.

Source: The Journal of Physical Chemistry Letters

DOI: 10.1021/acs.jpclett.5c00103