Design of NiNC single atom catalyst layers and AEM electrolyzers for stable and efficient CO2-to-CO electrolysis: Correlating ionomer and cell performance

Deploying single-site NiNC catalysts in cathode catalyst layers of bipolar electrolyzer cells enables catalytic CO2 valorization to e-CO at industrially relevant yields and efficiencies. The performance of the cathode layers is controlled by the turnover frequency of the active sites as well as mass transfer to and from the active sites. While the atomic scale structure-reactivity relations of single-site NiNC catalysts have been extensively studied, the mass transfer characteristics of single atom catalyst layers were poorly discussed. In this work, we design, build, and test NiNC catalyst layers using a novel set of distinct ion exchange ionomer materials and correlate the performance of cathode catalyst layers with their reactivity and stability in full single MEA electrolyzer cells. The Sustainion anion exchange ionomer delivered optimal performance, yielding about 90% CO faradaic efficiency up to 300 mA cm-2 and 15 h stable performance at 200 mA cm-2. Our analysis attributes its favorable electrolyzer performance to its balanced conductivity and hydrophobicity, which mitigates electrode flooding while ensuring excellent ion and CO2 transfer rates even at high current densities.

Automated summary

Deploying single-site NiNC catalysts in cathode catalyst layers enables efficient and high-yield catalytic conversion of CO2 to e-CO in limited space. The performance of the cathode layers is controlled by the turnover frequency and mass transfer characteristics of the active sites. This study designed, built, and tested NiNC catalyst layers using distinct ion exchange ionomer materials and correlated their performance with reactivity and stability in full single MEA electrolyzer cells. The Sustainion anion exchange ionomer showed the best performance, achieving 90% CO faradaic efficiency at 200 mA cm-2 and stable performance for 15 hours. The favorable electrolyzer performance was attributed to its balanced conductivity and hydrophobicity, ensuring excellent ion and CO2 transfer rates even at high current densities.