Rapid and controllable in-situ self-assembly of main-group metal nanofilms for highly efficient CO2 electroreduction to liquid fuel in flow cells

The electrocatalytic reduction of CO2 is a promising pathway to generate renewable fuels and chemicals. However, its advancement is impeded by the absence of electrocatalysts with both high selectivity and stability. Here, we present a scalable in-situ thermal evaporation technique for synthesizing series of Bi, In, and Sn nanofilms on carbon felt (CF) substrates with a high-aspect-ratio structure. The resulting main-group metal nanofilms exhibit a homogeneously distributed and highly exposed catalyst surface with ample active sites, thereby promoting mass transport and ad-/desorption of reaction intermediates. Benefiting from the unique fractal morphology, the Bi nanofilms deposited on CF exhibit optimal catalytic activities for CO2 electroreduction among the designed metal nanofilms electrodes, with the highest Faradaic efficiency of 96.9% for formate production at -1.3 V vs. reversible hydrogen electrode (RHE) in H-cell. Under an industrially relevant current density of 221.4 mA.cm(-2) in flow cells, the Bi nanofilms retain a high Faradaic efficiency of 81.7% at -1.1 V (vs. RHE) and a good long-term stability for formate production. Furthermore, a techno-economic analysis (TEA) model shows the potential commercial viability of electrocatalytic CO2 conversion into formate using the Bi nanofilms catalyst. Our results offer a green and convenient approach for in-situ fabrication of stable and inexpensive thin-film catalysts with a fractal structure applicable to various industrial settings.