CO ₂ -to-formate electrocatalysis in Bi-carbon fiber aerogels via coupled structural and electronic effects

The electrochemical CO₂ reduction to formate represents a promising route for carbon neutrality. However, current bismuth (Bi)-based catalysts suffer from limited active site exposure, poor charge transfer kinetics, and rapid performance degradation. Herein, we report a three-dimensional (3D) carbon fiber aerogels (CFAs) with a porous network architecture supporting well-distributed Bi nanoparticles (BiNPs) that synergistically address these challenges via geometrical structure and interfacial electronic modulation. The 3D porous network of the catalyst offers a high specific surface area of 534.39 m²·g^-1, promoting CO₂ adsorption and efficient charge transport. Electrochemical characterization reveals that the 0.02 M BiNPs@CFAs catalyst achieves a Faraday efficiency of formate (<em>FE</em><em>_formate</em>) of 96.73±1.45% at -1.0 V vs. RHE, while sustaining a high partial current density of -221.7 mA∙cm^-2 in the flow-cell operation. After continuous operation for 72 hours, the <em>FE</em><em>_formate</em> values remained above 90.6%. In-situ electrochemical Fourier transform infrared spectroscopy (in-situ FTIR) and the density functional theory (DFT) calculations confirm that Bi active sites effectively stabilize the *OCHO intermediate, a key step in formate formation. This work establishes new ideas for designing efficient and stable electrocatalysts through synergistic structural and electronic modulation by metal nanoparticles and aerogel architectures.