Nanostructured β-Bi2O3 Fractals on Carbon Fibers for Highly Selective CO2 Electroreduction to Formate

3D Bi2O3 fractal nanostructures (f-Bi2O3) are directly self-assembled on carbon fiber papers (CFP) using a scalable hot-aerosol synthesis strategy. This approach provides high versatility in modulating the physiochemical properties of the Bi2O3 catalyst by a tailorable control of its crystalline size, loading, electron density as well as providing exposed stacking of the nanomaterials on the porous CFP substrate. As a result, when tested for electrochemical CO2 reduction reactions (CO2RR), these f-Bi2O3 electrodes demonstrate superior conversion of CO2 to formate (HCOO-) with low onset overpotential and a high mass-specific formate partial current density of -52.2 mA mg(-1), which is approximate to 3 times higher than that of the drop-casted control Bi2O3 catalyst (-15.5 mA mg(-1)), and a high Faradaic efficiency (FEHCOO-) of 87% at an applied potential of -1.2 V versus reversible hydrogen electrode. The findings reveal that the high exposure of roughened beta-phase Bi2O3/Bi edges and the improved electron density of these fractal structures are key contributors in attainment of high CO2RR activity.