Metal Phthalocyanine-Derived Single-Atom Catalysts for Selective CO₂ Electroreduction under High Current Densities

Area of Science:

• Catalysis
• Electrochemistry
• Materials Science

Background:

• Single-atom catalysts (SACs) in nitrogen-doped carbon matrices (M-N/C) are promising for CO2 reduction reaction (CO2RR).
• Economic viability is hindered by low faradaic efficiency (FE) and instability under high current density.
• Existing methods using metal nitrates result in lower metal loading and higher variation.

Purpose of the Study:

• To develop highly active and selective SACs for CO2RR using cyano-substituted metal phthalocyanines.
• To improve metal loading and reduce variation in SAC synthesis.
• To evaluate catalyst performance in both H-cell and gas-diffusion electrode (GDE) setups.

Main Methods:

• Synthesized SACs from cyano-substituted metal phthalocyanines (MePc-CN) in ZIFs, denoted as Me-SACs (Pc).
• Compared Me-SACs (Pc) with counterparts from metal nitrates (Me-SACs (S)).
• Tested catalyst activity, selectivity, and stability in H-cell and GDE setups at various current densities.

Main Results:

• Me-SACs (Pc) exhibited higher activities and selectivities than Me-SACs (S).
• Iron SAC (Fe-SAC (Pc)) showed limited CO selectivity (50% FEco) at -100 mA cm-2 in GDE.
• Nickel SAC (Ni-SAC (Pc)) achieved >96% FEco from -10 to -200 mA cm-2 and operated stably for 16 h at -200 mA cm-2.

Conclusions:

• Phthalocyanine-derived SACs offer efficient construction with higher metal loading and less variation.
• Ni-SAC (Pc) demonstrates excellent performance comparable to precious metal catalysts and state-of-the-art SACs.
• Ni-SAC (Pc) is a promising candidate for practical electrolyzer devices for CO2RR.