Effects of electrochemical active surface area of Cu on electrochemical CO2 reduction in acidic electrolyte using Cu nanoparticles on surfactant-treated carbon

Abstract

Electrochemical carbon dioxide reduction reaction (CO2RR) presents a viable approach for transforming CO2 into valuable products. Traditional employment of neutral or alkaline electrolytes in CO2RR aims to avoid the hydrogen evolution reaction (HER). However, the usage of such electrolytes has intrinsic limitations on the availability of CO2 due to homogeneous equilibrium reactions, resulting in high energy costs for electrolyte regeneration. Lowering the pH of electrolytes can mitigate this concern and facilitate industrially relevant efficiencies. While recent studies show promising results for CO2RR in acidic environments using flow cells, the translation of conventional electrocatalysts from neutral or alkaline conditions to acidic conditions remains unclear. Hence, our investigation focuses on assessing the impact of surfactant-modified synthesis methods on CO2RR performance in acidic electrolytes.We first synthesized Cu nanoparticles on surfactant-treated carbon black by employing various surfactants: hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate, and Triton X-100, representing cationic, anionic, and nonionic surfactants, respectively. The objective of this synthesis was to investigate how surfactants influence the size and distribution of Cu nanoparticles (Cu NPs), the electrochemical active surface area (ECSA) of Cu, and, consequently, the performance of CO2RR in acidic electrolytes. The findings reveal that Cu NPs on carbon black show a different profile of size and distribution depending on the surfactant used for synthesis, resulting in varied ECSA. In addition, ECSA plays a crucial role in the production of C2H4 in an acidic medium, determining the onset potential and production rate of C2H4 while maintaining original Cu activity. In summary, surfactant treatment not only controls the size but also enables the uniform distribution of Cu NPs on carbon black. Consequently, Cu NPs exhibiting larger ECSA demonstrate enhanced efficiency in the production of C2H4 compared to counterparts with smaller ECSA under acidic environment.