Effect of rf-Plasma Treatment on the Activity and Selectivity of Me-N-C Electrocatalysts for the Oxygen Reduction Reaction
Authors: Weidler Natascha , Babu Deepu J. , Martinaiou Ioanna , Paul Stephen , Wagner Stephan , Shahraei Ali , Janßen Arne , Stark Robert W. , Schneider Jörg J. , Kramm Ulrike Ingrid 
Published: February 2020

In view of the transfer from fossil fuels to renewable energies, electrochemical reactions offer the chance of a fast and environmentally friendly production of chemicals or the transfer of chemical energy into electric energy (e.g. via fuel cells). While Me-N-C catalysts are already well-established as promising alternative to Pt/C in fuel cell applications [1], some of them might also be of interest for the electrochemical production of H2O2 (hydrogenperoxide) as an intermediate product.[2, 3] So far the largest efforts in electrochemical production of hydrogen peroxide are made by using supported metal (e.g. Pd, Au-Pd, Pd-Hg) nanoparticles [4, 5] and nitrogen coordinated metal complexes [6, 7] but recently also non-precious MNC catalysts have attracted attention due to their high ORR activity.[7-9]

In a previous publication we have shown that the presence of protonated nitrogen groups can enhance the ORR activity of Fe-N-C catalysts.[10] In addition theoretical calculations reveal that the largest enhancement in terms of required overpotential would be expected for the combination of MnN4 sites with carboxylic group.[11] In this work, we try to apply this promotor concept to our MNC catalysts (M= Co, Fe, Mn) by introducing targeted carboxylic groups via plasma treatments in different gas atmospheres (O2, CO2). Fe-N-C was selected as most promising candidate for FC application, Co-N-C as possible candidate for hydrogen peroxide formation and Mn-N-C due to previous findings on the improvement of the overpotential by carboxylic groups.[11] Rotating ring disk (RRDE) studies were performed to investigate the positive effect of plasma treatments on the activity and selectivity of the MNC catalysts. In addition, the initial and the modified MNCs were characterized using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to identify the plasma induced structural changes and their effect on the activity and selectivity data.

References:

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