Metalloporphyrin Monolayers as Tunable Platforms for CO₂ Electroreduction.

Area of Science:

• Electrochemistry
• Materials Science
• Surface Chemistry

Background:

• Electrocatalytic CO2 reduction (CO2RR) is crucial for sustainable energy, but understanding catalyst structure-activity relationships at electrode interfaces remains challenging.
• Heterogenized molecular catalysts offer tunable active sites, yet precise control over their organization is difficult.
• Accurate definition of active site distribution, surface density, and structural organization is key to optimizing CO2RR performance.

Purpose of the Study:

• To develop structurally well-defined model systems for studying electrochemical CO2 reduction (CO2RR).
• To investigate the impact of active site distribution and surface composition on CO2RR performance.
• To establish a platform for probing structure-activity relationships in molecular electrocatalysis with high precision.

Main Methods:

• Fabrication of self-assembled monolayers of metal porphyrins (Fe and Cu) on graphite electrodes.
• High-resolution scanning tunneling microscopy (STM) for characterizing monolayer structure, active site distribution, and surface composition.
• Electrochemical CO2 reduction (CO2RR) measurements, including Faradaic efficiency (FE) determination and isotopic labeling experiments.
• Construction and analysis of bicomponent monolayers to study composition-activity relationships.

Main Results:

• Crystalline, uniformly distributed metal porphyrin monolayers with periodicities of ~1.5 nm were observed via STM.
• Fe porphyrin monolayers showed higher Faradaic efficiencies (FEs) for CO production compared to Cu porphyrin analogues.
• Isotopic labeling confirmed that product CO originates from the CO2 source.
• CO2RR activity decreased systematically with increasing coverage of catalytically inactive porphyrin in bicomponent monolayers.

Conclusions:

• Molecularly ordered porphyrin monolayers serve as an effective platform for precise investigation of structure-activity relationships in electrocatalytic CO2 reduction.
• STM provides quantitative assessment of surface composition and structure, crucial for understanding catalyst performance.
• This approach enables detailed studies of molecular electrocatalysis, paving the way for optimized CO2RR catalysts.