Correlating Site Density and Catalytic Activity for Non-Precious ORR Electrocatalysts

Carbon materials doped with iron and nitrogen (Fe-N-C) are highly active, precious metal-free catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes^1-4. However, accurate measurement of their intrinsic turn-over-frequency (TOF) and active site density based on metal centers in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here, we report a successful quantification of bulk and surface-based active site density and associated TOF values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption, and ⁵⁷Fe Mößbauer spectroscopy techniques. Our general approach yields novel experimental descriptors for intrinsic activity and active site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity.             

1.            Wu, G.; Zelenay, P., Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction. Acc. Chem. Res. 2013, 46, 1878-1889.

2.            Sahraie, N. R.; Paraknowitsch, J. P.; Göbel, C.; Thomas, A.; Strasser, P., Noble-Metal-Free Electrocatalysts with Enhanced ORR Performance by Task-Specific Functionalization of Carbon using   Ionic Liquid Precursor Systems. J. Am. Chem. Soc. 2014, 136, 14486-14497.

3.            Chung, H. T.; Won, J. H.; Zelenay, P., Active and stable carbon nanotube/nanoparticle composite electrocatalyst for oxygen reduction. Nature Communications 2013, 4.

4.            Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science 2011, 332, 443-447.