Bi₂O₃ Nanosheets Grown on Carbon Nanofiber with Inherent Hydrophobicity for High-Performance CO₂ Electroreduction in a Wide Potential Window.

Abstract

The ever-increasing concern for adverse climate changes has propelled worldwide research on the reduction of CO₂ emission. In this regard, CO₂ electroreduction (CER) to formate is one of the promising approaches to converting CO₂ to a useful product. However, to achieve a high production rate of formate, the existing catalysts for CER fall short of expectation in maintaining the high formate selectivity and activity over a wide potential window. Through this study, we report that Bi₂O₃ nanosheets (NSs) grown on carbon nanofiber (CNF) with inherent hydrophobicity achieve a peak formate current density of 102.1 mA cm^-2 and high formate Faradaic efficiency of >93% over a very wide potential window of 1000 mV. To the best of our knowledge, this outperforms all the relevant achievements reported so far. In addition, the Bi₂O₃ NSs on CNF demonstrate a good antiflooding capability when operating in a flow cell system and can deliver a current density of 300 mA cm^-2. Molecular dynamics simulations indicate that the hydrophobic carbon surface can repel water molecules to form a robust solid-liquid-gas triple-phase boundary and a concentrated CO₂ layer; both can boost CER activity with the local high concentration of CO₂ and through inhibiting the hydrogen evolution reaction (HER) by reducing proton contacts. This water-repelling effect also increases the local pH at the catalyst surface, thus inhibiting HER further. More significantly, the concept and methodology of this hydrophobic engineering could be broadly applicable to other formate-producing materials from CER.