Dissecting Key Factors Influencing Electrochemical Conversion of Carbon Solutions over Nickel Single Atoms

The direct electrochemical conversion of bicarbonate solutions (i.e., captured CO₂) has emerged as a sustainable approach for integrating CO₂ capture and utilization compared to the traditional independent and sequential route. However, the process of bicarbonate conversion is poorly understood, impeding the development of this new technology. Here, the study explores the critical factors influencing bicarbonate solution conversion over Ni single-atom catalysts, including catalyst structure, carbon source, electrolysis temperature, and electrolyzer type. The catalyst with better exposure of Ni sites and smaller charge transfer resistance exhibits higher activity for the conversion of both gaseous CO₂ and bicarbonate solutions. In situ Raman spectroscopy and DFT calculations reveal that bicarbonate conversion follows a two-step pathway, that is, bicarbonate dissociation to generate CO₂ followed by CO₂ reduction to form CO over Ni sites. Increasing the electrolysis temperature promotes the dissociation of HCO₃ ^- and boosts the CO production. More interestingly, switching the Ar/CO₂ atmosphere affects the efficiency of CO production in H-cell but has no influence in membrane electrode assembly cell. Such a phenomenon is attributed to different CO₂ sources. This work sheds light on the electrochemical conversion of various carbon solutions and establishes the connection between the conversion of gaseous CO₂ and captured CO₂.