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

Abstract 3D Bi 2 O 3 fractal nanostructures (f‐Bi 2 O 3 ) 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 Bi 2 O 3 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 CO 2 reduction reactions (CO 2 RR), these f‐Bi 2 O 3 electrodes demonstrate superior conversion of CO 2 to formate (HCOO − ) with low onset overpotential and a high mass‐specific formate partial current density of −52.2 mA mg −1 , which is ≈3 times higher than that of the drop‐casted control Bi 2 O 3 catalyst (−15.5 mA mg −1 ), and a high Faradaic efficiency (FE HCOO − ) of 87% at an applied potential of −1.2 V versus reversible hydrogen electrode. The findings reveal that the high exposure of roughened β‐phase Bi 2 O 3 /Bi edges and the improved electron density of these fractal structures are key contributors in attainment of high CO 2 RR activity.