The electrochemical reduction of carbon dioxide (CO₂) into valuable chemicals and fuels is a pivotal strategy in mitigating climate change by curbing greenhouse gas emissions. Although copper (Cu) and Cu-alloys have shown promise as catalysts for CO₂ reduction, they tend to produce a complex mixture of products, including carbon monoxide, methane, formate, ethylene, and ethanol, with no clear guiding principles for selective product formation or understanding of the temporal evolution of production distribution.
Recent studies using water-in-salt-electrolytes (WISE) for CO₂ reduction have demonstrated their potential to significantly modulate catalytic output. The decreased water activity in highly concentrated electrolytes leads to substantial increases in the formation of C2+ products. For example, the onset potential of C₂H₄ was found to shift nearly 200 mV when the water activity drops from 0.97 to nearly 0.5 (Figure 1). This presentation will delve into the intricate interplay between water activity and gas composition in influencing the kinetic branching between C1 and C2+ pathways during CO reduction, a pivotal intermediate of CO₂ reduction. Online electrochemical mass spectrometry (ECMS) results provide temporal snapshots of product distributions during CO reduction, as influenced by variations in water activity and gas composition. This approach facilitates the determination of reaction orders for the respective kinetic pathways, shedding light on the intricate surface phenomena governing the steady-state selectivity of the electrode. By elucidating the mechanisms that govern CO₂ conversion, we contribute to global efforts to combat climate change and reduce emissions, paving the way for more sustainable and efficient CO₂ utilization technologies.

<b>Figure </b><b>1</b> Onset potential of C<sub>2</sub>H<sub>4</sub> during CO<sub>2</sub> reduction in varying concentrations of NaClO<sub>4</sub> effectively tuning the water activity.

Figure 1 Onset potential of C₂H₄ during CO₂ reduction in varying concentrations of NaClO₄ effectively tuning the water activity.