Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts

Nastaran Ranjbar Sahraie, Ulrike I Kramm, Julian Steinberg, Yuanjian Zhang, Arne Thomas, Tobias Reier, Jens-Peter Paraknowitsch, Peter Strasser
Nature Communications 2015, 6: 8618
Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres 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 turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and (57)Fe Mössbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the 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.


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