Formation of Bismuth Nanosheets on Copper Foam Coupled with Nanobubble Technology for Enhanced Electrocatalytic CO2 Reduction

Abstract

The recycling of industrially emitted CO2 is an urgent environmental task. Electrochemical reduction of CO2 into valuable chemical products presents an attractive approach. However, due to the inherent high chemical stability of CO2 molecules and the complex sequence of multiple electron and proton transfer steps involved in the CO2 reduction reaction (CO2RR), current electrocatalytic systems commonly face challenges such as low CO2 conversion rates and energy utilization efficiency, limited current density, and short electrode lifespan. Herein, we adopt a simple three-step process involving in situ chemical etching, thermal oxidation, and electrochemical reduction to construct bismuth nanosheets (Bi NSs) with abundant lattice dislocations on copper foam, and introduce nanobubble technology to enhance the CO2RR process. In an H-type cell with flowing electrolyte, our Bi NSs/CF electrode achieved a remarkable formate Faradaic efficiency (FEFormate) of 95.36% at a low applied potential of -1.08 V vs. RHE (reversible hydrogen electrode), along with a significant formate partial current density (JFormate) of ~38 mA cm-2 and an energy efficiency of ~60%. Even within a wider operating window (-0.78 to -1.18 V), the FEFormate remained at a high level (>91%). Importantly, the application of nanobubble technology made the CO2 conversion rate increase nearly fivefold. Further density functional theory calculations confirmed that the Bi NSs with lattice dislocations on the Bi NSs/CF surface can effectively stabilize the *OCHO intermediate, thereby achieving high activity and selectivity for CO2RR. This work highlights the significant roles of nanobubble technology, size-dependent catalysis, and crystal defect engineering strategies in the field of electrocatalysis, elucidating the activity sources of the developed catalyst in the electrochemical CO2 reduction process, and providing valuable insights for the design and development of high-performance electrocatalytic systems for CO2RR and other fields.