2023. 07. 18
Electrochemical CO2 reduction reaction for sustainable chemical cycle
Yun Jeong Hwang 1*
1Department of Chemistry, Seoul National University (SNU), Republic of Korea
E-mail address: yjhwang1@snu.ac.kr
Electrochemical CO2 reduction (CO2R) can be integrated with renewable energy sources and water can be utilized as a direct proton source which is promising to provide a sustainable net-zero carbon cycle. However, using water as the proton source causes undesired competitive hydrogen evolution reaction (HER), and thus it is crucial to control selectivity for CO2R. Various metal-based electrocatalysts have been investigated to convert CO2 to CO, formate, ethylene, ethanol, or other C2+ chemicals. Multiple reaction pathways and reaction intermediates are shared and thus product distribution is sensitively affected by nanostructured active sites both in a conventional H-cell as well as a membrane electrode assembly (MEA) electrolyzer. Understanding intrinsic and extrinsic factors are important to achieve selective CO2R to target product. In this talk, I will discuss efforts to understand the morphology changes of the nanocatalyst. Cu-based catalysts can experience morphology changes during the pre-treatment step and reduction reaction conditions, and increasing the domain boundaries can contribute to enhanced activity for CO2R over HER. In the GDE-based membrane-electrode-assembly (MEA) electrolyzer, increasing the surface roughness and grain boundaries have shown high selectivity for C2+ chemicals similar to the conventional H-Cell type electrolyzer. Meanwhile, from a practical point of view, researchers also propose direct conversion of the captured CO2 by the electrochemical process. We demonstrate that a Ni-N-C catalyst has high selectivity for electrochemical CO2 conversion to CO production due to the relatively high activation energy for HER compared to that of the CO2R-to-CO reaction. This contributes to increasing CO2 conversion efficiency even under low concentrations of available CO2 gas. In addition, the Ni-N-C was found to have low sensitivity to the type of alkali metal cation or the type of amine. Modulation of the catalyst-electrolyte interface can provide new opportunities to promote challenging catalytic reactions....
