Scalable flame spray-derived bismuth catalysts enable efficient CO2 electrolysis revealed by FIB-SEM nano-tomography and ICP-MS EDX profiling

CO 2 electrolysis is a promising route to convert CO 2 into value-added chemicals. Here, we use flame spray pyrolysis (FSP) as a rapid and scalable method to synthesize Bi 2 O 3 nanospheres and evaluate their formate production in a gas diffusion electrode flow electrolyzer. Under reaction conditions, Bi 2 O 3 converts in situ into bismuth subcarbonate, delivering >90% formate Faradaic efficiency across −0.6 to −1.6 V vs. reversible hydrogen electrode (RHE), reaching a formate partial current density of −700 mA.cm −2 at −1.8 V. This performance is nearly twice that of electrochemically deposited dendritic Bi 2 O 3 . To elucidate the origin of this high performance, a combined tomography approach based on focused ion beam-scanning electron microscopy (FIB-SEM) nano-tomography and inductively coupled plasma-mass spectrometry (ICP-MS) EDX cross-sectional profiling was introduced to track catalyst layer morphology and electrolyte-induced flooding. The FSP-derived catalyst forms a compact layer near the microporous layer, confining flooding to the catalyst microporous interface and improving operational stability. This work provides mechanistic insight and characterization guidelines for designing durable, high-performance electrodes for CO 2 electrolysis.