Catalytic Layer Microstructure in Pulsed Electrodeposited Bismuth-Based Gas Diffusion Electrodes Used for CO₂ Reduction to Formate

The electrochemical carbon dioxide reduction (COr) reaction offers a viable method for converting waste carbon dioxide into valuable products. Gas diffusion electrodes (GDEs) are crucial for meeting the high current density demands associated with the upscaling of CO₂r. In this research, we investigated how the microstructure of the catalytic layer in a Bi-based GDE and the catalyst nanostructure can be modified by altering the electrodeposition duty cycle. Furthermore, we explored how the microstructure influences the key performance indicators of the GDE. The outcomes demonstrated that decreasing the duty cycle of pulsed electrodeposition enhances the catalyst dispersibility within the three-dimensional catalytic layer, thereby improving catalytic performance. Additionally, reducing the duty cycle increased the nucleation site density, leading to smaller catalysts and denser catalytic sites, further enhancing the catalytic performance. By employing a Sustainion ionomer and a 60-80 μm thick catalytic layer, we achieved a current density exceeding −210 mA/cm² (at −1.0 V vs RHE) with 100% Faradaic efficiency for formate in a semi-batch testing bed. This research provides novel insights into catalytic layer design and offers a strategy to modify it to meet the stringent industrial benchmarks.