Mixed Metal Phthalocyanine-Modified Carbon Nanotubes for Bifunctional Oxygen Reduction and Evolution Reaction

Abstract

In this ever-expanding world, researchers are focused on changing how we consume energy. Progress has been made over time, but the devices such as low-temperature polymer electrolyte fuel cells and metal-air batteries that can replace the conventional fossil fuel engines still use noble metal catalysts,1 which hinders the mass production and long-term usage of the devices. Transition metal macrocyclic (MN4-type) catalysts are good alternatives for the noble metal catalysts due to their low-price and promising electrocatalytic activity.2 Thus, the aim of this study was to develop the bifunctional ORR/OER electrocatalysts using mixed transition metal phthalocyanine-modified multi-walled carbon nanotubes (MWCNT) by simple pyrolysis method.3 Among the prepared bifunctional catalysts, FeCoN-MWCNT showed the superior electrocatalytic ORR activity in alkaline media with half-wave potential of 0.86 V vs RHE and FeNiN-MWCNT catalyst exhibited the exceptional OER activity with E j=10 mA cm–2 of 1.58 V (see Fig. 1a, b). Physical characterization of the prepared catalysts was investigated with (scanning) electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Further, catalysts were tested in anion-exchange membrane fuel cells (AEMFCs) as cathode material and very good peak power density of 692 mW cm–2 was obtained for FeCoN-MWCNT (see Fig. 1c). FeNiN-MWCNT was tested in anion-exchange membrane electrolyzer (AEMEL) and showed comparable results with state-of-the-art RuO2 catalysts (Fig. 1d). Altogether, this study unveils the insight into potential ways of preparing the bifunctional ORR/OER electrocatalysts with transition metal macrocyclic-based compounds. References S. Hussain, H. Erikson, N. Kongi, A. Sarapuu, J. Solla-Gullón, G. Maia, A. M. Kannan, N. Alonso-Vante, K. Tammeveski, Int. J. Hydrogen Energy, 45, 31775-31797 (2020).A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, K. Tammeveski, J. Mater. Chem. A, 6, 776–804 (2018).Y. Kumar, E. Kibena-Põldsepp, J. Kozlova, M. Rähn, A. Treshchalov A. Kikas, V. Kisand, J. Aruväli, A. Tamm, J. C. Douglin, S. J. Folkman, I. Gelmetti, F. A. Garcés-Pineda, J. R. Galán-Mascarós, D. R. Dekel, K. Tammeveski, ACS Appl. Mater. Interfaces, 13, 41507–41516 (2021). Figure 1