Cobalt porphyrins supported on carbon nanotubes as model catalysts of metal-N4/C sites for oxygen electrocatalysis

Abstract

Using model catalysts, it is revealed that electron-rich M-N 4 /C sites are more favorable for oxygen electrocatalysis when noncovalently adsorbed on carbon supports. • New insights are revealed that electron-rich M-N 4 /C sites (M = Co 2+ ) more facilitate ORR and OER. • Employing model catalysts to investigate the regime of electron density of M-N 4 /C sites on ORR and OER. • Rational design concept of model catalysts towards mechanism investigations for electrocatalysis. Transition-metal based M-N 4 /C catalysts are appealing for electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Employing model catalysts, which have well-defined molecular structures and coordination environments, to investigate electrocatalytic performance of M-N 4 /C sites for ORR and OER is of fundamental significance. Herein, we reported the use of Co tetra(phenyl)porphyrin 1 and Co tetra(pentafluorophenyl)porphyrin 2 as models to probe the role of Co-N 4 /C sites for oxygen electrocatalysis. We showed that Co porphyrin 1 is more efficient than its structural analogue 2 for oxygen electrocatalysis in alkaline aqueous solutions, indicating that the electron-rich Co-N 4 /C site is more favored when noncovalently adsorbed on carbon supports. This work inspires rational design of reaction-oriented catalysts for sustainable energy storage and conversion technologies.