Enhancing CO2 Reduction Efficiency through Electrolyte Immersion in Hierarchical Bismuth-Nickel Catalysts

Nanostructures are critical to improve contact area with an electrolyte and catalytic efficiency for the CO2 reduction reaction (CO2RR). However, their hydrophobicity conflicts with the intended increase in contact area and complicates determination of active contact area. Here, bismuth-nickel (BiNi) micro-nano hierarchical catalysts for CO2RR were studied to understand the effects of electrolyte-catalyst contact area variation with immersion duration in an aqueous electrolyte. The immersed BiNi samples showed about 13.4-fold higher formate production compared to the pristine BiNi sample. The 2-day pre-immersed BiNi sample exhibited Faradaic efficiencies (FE%) of ~80.1% for formate and ~10% for H2 with a current density of 10.2 mA cm-2 at -1.5 V vs. Ag/AgCl. In contrast, the pristine BiNi catalysts exhibited an FE% of ~12.9% for formate and ~76.3% for H2 with a current density of 5.38 mA cm-2. Our experimental results reveal that improved contact between the electrolyte and catalyst surface through pre-immersion can lead to enhanced CO2RR efficiency of formate production in hierarchical BiNi catalysts.