Efficient CO2 Reduction to Formate with Nano-Roughened Cu–Bi Alloy Hollow Fiber Electrodes

The electroreduction of CO2 to formate is of significant interest due to its potential for sustainable fuel and chemical production. Hollow fiber electrodes, which integrate gas diffusion and catalytic layers, offer structural advantages. These advantages enhance gas–solid–liquid-phase reactions, making them particularly beneficial for CO2 electroreduction. This work reports a copper–bismuth alloy hollow fiber with a nanostructured surface, designed with specific metal ratios and transformed into a sulfur surface-modified copper–bismuth alloy hollow fiber (Cu7S4–CuBi HF) electrode with nanoflower structures. CO2-penetration mode enhances formate current density and Faradaic Efficiency (FE) while suppressing the hydrogen evolution reaction (HER), due to the fiber's unique gas transport. The nanoflower morphology increases the electrochemical active surface area, boosting current densities. This design achieved a formate FE of 91.27% at −0.9 V vs RHE and a current density of 80.12 mA cm–2, outperforming many existing Cu@Bi electrocatalysts. This success is due to the innovative surface design and the distinct structural features of the hollow fiber electrodes.