Identification of a Durability Descriptor for Molecular Oxygen Reduction Reaction Catalysts

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• Developing durable, platinum-group-metal-free oxygen reduction reaction (ORR) catalysts is crucial for widespread fuel cell adoption.
• Iron-based metallophthalocyanines (MPcs) are promising candidates for ORR catalysis.

Purpose of the Study:

• To investigate the activity and durability of seven iron-based MPc ORR catalysts with varying substituent groups.
• To identify structure-property relationships governing MPc catalyst degradation.

Main Methods:

• Experimental measurements of ORR activity and durability.
• Density functional theory (DFT) calculations to determine reaction mechanisms and energy barriers.
• Analysis of the relationship between catalyst structure and degradation pathways.

Main Results:

• MPc catalysts exhibited similar ORR activity but significantly different durabilities.
• A linear correlation was found between the energy difference of the hydrogenated intermediate and demetalated structure (ΔE_demetalation) and the degradation reaction barrier energy.
• ΔE_demetalation also serves as a descriptor for metallocorrole systems, with proton availability influencing durability.

Conclusions:

• Catalyst durability is strongly linked to the ΔE_demetalation descriptor.
• Understanding these degradation pathways is key to designing more robust, platinum-free ORR catalysts for fuel cells.