Establishing the stability number descriptor for Fe-N-C fuel cell electrocatalysts

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Iron-nitrogen-carbon (Fe-N-C) electrocatalysts are promising for oxygen reduction reactions (ORR) in polymer electrolyte fuel cells.
• Their widespread application is hindered by moderate operational stabilities.
• Previous work established a stability (S-) number descriptor for Fe-N-C catalysts in alkaline media at room temperature.

Purpose of the Study:

• To generalize and establish the S-number descriptor for Fe-N-C electrocatalysts.
• To investigate the influence of pH, potential, current density, and temperature on Fe dissolution.
• To extend the applicability of the S-number descriptor to acidic electrolytes and higher temperatures.

Main Methods:

• Experimental investigation of Fe-N-C electrocatalyst dissolution behavior under varying conditions (pH, potential, current density, temperature).
• Application of the S-number descriptor to correlate ORR rates and Fe dissolution.
• Development of a kinetic model to explain pH dependence of the S-number in acidic media.

Main Results:

• The S-number concept is validated for ORR and Fe dissolution in alkaline electrolytes at 70 °C.
• In acidic media, the S-number is dependent on ORR current density due to significant local pH increases within the catalyst layer.
• The S-number descriptor, accounting for pH dependence, effectively benchmarks Fe-N-C stability in acidic electrolytes.

Conclusions:

• The S-number descriptor is a versatile tool for evaluating Fe-N-C electrocatalyst stability under diverse conditions.
• The descriptor's applicability extends to acidic electrolytes by considering pH-dependent effects.
• The S-number concept shows potential for broader application in rational activity and stability screening of various electrocatalysts and reactions.